TRƯỜNG ĐẠI HỌC KHOA HỌC TỰ NHIÊN --------------------- HỒ ... (125).pdf · Danh mục các ký hiệu, các chữ viết tắt PLA Poly-axit lactic PLLA PolyL-axit

I HC QUC GIA H NI

TRNG I HC KHOA HC T NHIN

---------------------

H TH HOA

NGHIN CU TNG HP V NG DNG POLYLACTIC ACID

LUN VN THC S KHOA HC

H Ni - 2015

I HC QUC GIA H NI

TRNG I HC KHOA HC T NHIN

---------------------

H TH HOA

NGHIN CU TNG HP V NG DNG POLYLACTIC ACID

Chuyn ngnh: Ha hu c

M s: 60440114

LUN VN THC S KHOA HC

Hng dn KH: TS. Hong Mai H

TS. Trn Mnh Tr

H Ni - 2015

Nghin cu tng hp v ng dng polylactic acid H Th Hoa

MC LC

Chng 1: TNG QUAN .............................................................................................. 1

1.1. Tng hp PLA t rm r ....................................................................... 1

1.1.1. Ngun rm r ph liu Vit Nam ................................................................. 1

1.1.2. Axit lactic ................................................................................................................ 3

1.1.3. Qu trnh ln men tng hp axit lactic t rm r. ..................................... 5

1.1.4. Lactide ...................................................................................................................... 7

1.1.5. Poly-axit lactic (PLA) .......................................................................................... 8

1.1.6. Tng hp PLA ......................................................................................... 11

1.2. c trng cu trc ca PLA ............................................................... 27

1.2.1. Vi cu trc, hnh thi hc v hnh dng. ...................................................... 27

1.2.2. Khi lng mol v cu trc phn t ............................................................. 28

1.2.3. S chuyn trng thi nhit: ............................................................................. 28

1.2.4. tinh khit quang hc v s raxemic ha ................................................ 29

1.2.5. S phn hy ca PLA ........................................................................................ 30

1.3. Cc vt liu tng hp ca PLA............................................................ 32

1.3.1. Nghin cu tng hp PLA/ PEG .................................................................... 32

1.3.2. Tng hp copolyme ca axit lactic v poly (ethylene glycol). ................ 37

1.3.3. Nano clay ............................................................................................................... 39

1.3.4. Nano bc ................................................................................................................ 42

Chng 2: THC NGHIM ...................................................................................... 44


2.1. Ha cht v thit b .............................................................................. 44

2.1.1. Tng hp poly-axit lactic .................................................................................. 44

2.1.3. Ch to cc vt liu t hp t poly-axit lactic ............................................ 45

2.2. Quy trnh th nghim ............................................................................ 45

2.2.1. Tinh ch axit lactic ............................................................................................. 45

2.2.2. Tng hp PLA ..................................................................................................... 47

2.2.3. Phng php to t hp PLA-PEG .............................................................. 53

2.2.4. Tng hp copolyme PLA-PEG ....................................................................... 54

2.2.5. Phng php ch to nanocomposite PLA-Clay....................................... 55

2.2.6. Ch to composite PLA/nano bc .................................................................. 58

2.3. Phng php nghin cu. .................................................................... 61

2.3.1. Nghin cu cu trc ............................................................................. 61

2.3.2. Nghin cu hnh thi hc, tnh cht nhit, c l ........................................ 61

2.3.3. Gia cng ................................................................................................................. 61

2.3.4. Nghin cu tnh khng khun ............................................................. 62

2.3.4.1. Chng vi sinh vt ................................................................................................ 62

2.3.4.5. Phng php nh gi tnh khng khun ca dung dch keo nano bc ......................................................................................................................................................63

2.3.4.6. nh gi tnh khng khun ca vt liu t hp PLA/nano bc ............ 64

Chng 3: KT QU .................................................................................................. 65

3.1. Tinh ch axit lactic. .............................................................................. 65


3.2. Nghin cu tng hp PLA ................................................................... 65

3.2.1. Nghin cu tng hp cht trung gian L-lactide ......................................... 65

3.2.2. Nghin cu tng hp PLA................................................................................ 80

3.2.3. Nghin cu cu trc, tnh cht ca PLA ..................................................... 84

3.3. Ch to vt liu t hp PLA ................................................................ 91

3.3.1. T hp PLA-PEG ............................................................................................... 91

3.3.2. Ch to copolyme PLA-PEG ........................................................................... 96

3.3.3. Ch to vt liu t hp nanocomposite PLA-Clay .................................. 100

3.3.4. Vt liu t hp PLA/ nano bc ..................................................................... 105

KT LUN ................................................................................................................. 112

TI LIU THAM KHO ......................................................................................... 113


Danh mc cc k hiu, cc ch vit tt

PLA Poly-axit lactic

PLLA PolyL-axit lactic

PE Polyetylen

PP Polypropylen

PVC Polyvinyl clorua

PC Polycacbonat

PET Polyetylen terephtalat

PA Polyamit

PMMA Polymetyl metacrylat


Danh mc cc bng biu

Bng 1. 1: Tnh cht vt l v ha hc ca axit lactic ............................................ 5

Bng 1. 2: Tnh cht vt l ca lactide.................................................................... 8

Bng 1. 3: Kh nng phn hy sinh hc ca mt s polyme .................................. 9

Bng 3. 1: Cc iu kin cho qu trnh loi nc axit lactic. .............................. 66

Bng 3. 2: nh hng ca thi gian phn ng n hiu sut phn ng tng hp

oligome PLA. ......................................................................................................... 68

Bng 3. 3: nh hng ca xc tc v hm lng n hiu sut to lactide ......... 69

Bng 3. 4: Cc thng s c la chn tng hp lactide ................................ 78

Bng 3. 5: S ph thuc khi lng phn t PLA vo cht khi mo. ................. 80

Bng 3. 6: nh hng ca cht ng khi mo n KLPT trung bnh ca PLA. . 84

Bng 3. 7: Cc iu kin tt nht cho qu trnh tng hp PLA ............................ 84

Bng 3. 8: S lng mu v khi lng phn t ca PLA ................................... 85

Bng 3. 9: Cc tnh cht c l ca PLA tng hp c v PLA thng mi ....... 91

Bng 3. 10: Cc tnh cht c l ca t hp PLA-PEG vi cc hm lng PEG

khc nhau. .............................................................................................................. 95

Bng 3. 11: Khi lng phn t ca cc mu PA1 v PA2 .................................. 98

Bng 3. 12: iu kin ti u to mng PLA-Clay nanocomposite ................ 100

Bng 3. 13: bn ko ca tm PLA-Clay nanocomposite vi cc t l clay khc

nhau. .................................................................................................................... 105

Bng 3. 14: Kh nng khng khun ca vt liu ph nano bc theo thi gian. . 111


Danh mc cc hnh nh

Hnh 1. 1: Sn lng rm r ti cc khu vc trong c nc (2010) ...................... 2

Hnh 1. 2: Cng thc cu to ca axit lactic .......................................................... 3

Hnh 1. 3: Cng thc cu to ca hai ng phn axit lactic: axit L(+)-lactic tri,

axit D(-)-lactic phi ................................................................................................. 4

Hnh 1. 4: S qu trnh ln men ng glucose vi khun lactic. .................... 7

Hnh 1. 5: Ba cu trc ca lactide .......................................................................... 8

Hnh 1. 6: Mt s sn phm c s dng nha phn hy sinh hc PLA ................ 10

Hnh 1. 7: Cc phng php tng hp PLA t axit lactic .................................... 11

Hnh 1. 8: S minh ha quy trnh tng hp lactide bng phng php trng

hp oligome axit lactic. ......................................................................................... 12

Hnh 1. 9: Cc bc trong qu trnh tng hp L-Lactide ..................................... 13

Hnh 1. 10: Qu trnh back - bitting to lactide .................................................... 14

Hnh 1. 11: C ch trng hp m vng cation lactide .......................................... 18

Hnh 1. 12: S khi mo ca phn ng trng hp m vng lactone .................... 19

Hnh 1. 13: Trng hp anionic ca (a) lactone, (b) lactide .................................. 20

Hnh 1. 14: C ch phi tr b sung ca trng hp lactone (a) v lactide (b) .. 21

Hnh 1. 15: Trng hp m vng lactide vi cht khi mo l ru .................... 23

Hnh 1. 16: S phn ng ca thic octonate vi cht khi mo l ru hoc

tp cht hnh thnh cht hot ng xc tc Sn-O-R ........................................ 24

Hnh 1. 17: Cc c ch ng phn ha: (a) s hn bin ha ester- bn axetal, (b)

phn ng SN2 ti mt trung tm bt i ................................................................ 32


Hnh 1. 18: M t cu trc ca triblock copolyme P(LLA-b-PEG-b-LLA) .......... 38

Hnh 1. 19: S tng hp mPEG-PLA ............................................................... 38

Hnh 1. 20: S tng hp poly (ethylene glycol) poly( axit lactic) copolyme

ui acetal ............................................................................................................. 39

Hnh 1. 21: Cu trc mng tinh th 2:1 ca MMT ............................................... 40

Hnh 1. 22: Nguyn l iu ch nano clay hu c bng cc cation amoni khc

nhau ....................................................................................................................... 41

Hnh 1. 23: Cu to mixen ca ht bc khi c v khng c s bo v ca cc cht

hot ng b mt. .................................................................................................. 43

Hnh 2. 1 Thit b tng hp lactide (a) v tinh ch lactide (b) ............................ 45

Hnh 2. 2: Quy trnh v tng s cho vic tch axit lactic bng cng ngh mng . 46

Hnh 2. 3: S quy trnh tch axit lactic bng phng php ester ha. ........... 47

Hnh 2. 4: S quy trnh tng hp PLA t axit lactic. ...................................... 52

Hnh 2. 5: Phng php to nano clay hu c ................................................... 56

Hnh 2. 6: Phng php ch to ht nanocomposite PLA-Clay .......................... 57

Hnh 2. 7: Quy trnh ch to ht nano bc, kt t to bt v phn tn trong

polyme ............................................................................................................... 59

Hnh 3. 1: Axit lactic sau khi ln men (a), Ph sc k HPLC xc nh mc

sch v s dng nh lng L-axit lactic to ra ............................................... 65

Hnh 3. 2: nh hng ca nhit phn ng n KLPT trung bnh ca oligome

PLA (thi gian phn ng 4h, p sut 10 mmHg). ................................................. 66


Hnh 3. 3: nh hng ca thi gian phn ng n KLPT trung bnh ca oligome

PLA (T = 200oC, P = 10 mmHg)........................................................................... 67

Hnh 3. 4: nh hng ca hm lng xc tc n t l L-lactide. ........................ 70

Hnh 3. 5: nh hng ca KLPT trung bnh ca oligome PLA n hiu sut tng

hp lactide. ............................................................................................................ 71

Hnh 3. 6: nh hng ca nhit phn ng n hiu sut chuyn ha. ............ 72

Hnh 3. 7: nh hng ca nhit phn ng n t l L-lactide. ........................ 73

Hnh 3. 8: nh hng ca thi gian n hiu sut tng hp lactide. ................... 74

Hnh 3. 9: nh hng ca p sut n hiu sut phn ng tng hp L-lactide. .. 75

Hnh 3. 10: S ph thuc hm lng meso-lactide vo thi gian tch loi ti cc

nhit khc nhau. ............................................................................................... 76

Hnh 3. 11: ph thuc hm lng Meso-lactide vo dung mi. ............................ 77

Hnh 3. 12: Ph IR ca L-lactide cha tinh ch ................................................... 78

Hnh 3. 13: Ph hng ngoi ca L-lactide tinh ch ......................................... 79

Hnh 3. 14: Ph 1H-NMR ca L-lactide ............................................................... 80

Hnh 3. 15: nh hng ca hm lng cht khi mo Sn(Oct)2 n hiu sut

chuyn ha phn ng tng hp PLA. .................................................................... 81

Hnh 3. 16: nh hng ca hm lng cht khi mo n KLPT trung bnh ca

PLA. ....................................................................................................................... 82

Hnh 3. 17: nh hng ca cc cht ng khi mo n hiu sut phn ng tng

hp PLA. ................................................................................................................ 83

Hnh 3. 18: Sc k GPC - phn b phn t lng ca PLA ............................ 86


Hnh 3. 19: Sc k GPC ca PLA phn t lng cao tng hp c ............. 86

Hnh 3. 20: Ph IR ca PLA .................................................................................. 87

Hnh 3. 21: Ph 1H-NMR ca PLA ....................................................................... 88

Hnh 3. 22: Ph cng hng t ht nhn 13C-NMR ca PLA ............................... 89

Hnh 3. 23: ng cong ng sut bin dng ca PLA. ................................ 90

Hnh 3. 24: S ph thuc ca monen xon ( nht) vo thi gian phi trn ..... 92

Hnh 3. 25: S ph thuc ca momen xon cc i vo hm lng PEG ............ 93

Hnh 3. 26: ng cong ng sut- bin dng trong th nghim o tnh cht c

l ca t hp PLA-PEG. ........................................................................................ 94

Hnh 3. 27: Cu trc copolyme PLA-PEG v v tr tng ng ca cc proton trn

cng hng t ht nhn NMR ............................................................................... 97

Hnh 3. 28: Ph cng hng t ht nhn .............................................................. 97

Hnh 3. 29: Ph hng ngoi ca copolyme tinh ch v ht copolyme PLA-PEG . 98

Hnh 3. 30: nh hin vi in t qut ca ht copolyme PLA-PEG. ...................... 99

Hnh 3. 31: Mng nanocomposite PLA-Clay vi hai dy khc nhau a) 5cm, b)

2cm ...................................................................................................................... 101

Hnh 3. 32: ph nhiu x ca (1) PLA, (2) nanocomposite 1% clay, (3)

nanocomposite 3% clay, (4) clay ........................................................................ 101

Hnh 3. 33. nh TEM ca PLA-Clay (1%) nanocomposite. ............................... 103

Hnh 3. 34: nh TEM ca PLA-Clay (3%) nanocomposite. ............................... 103

Hnh 3. 35: thm kh ca vt liu nanocomposite PLA-Clay vi hm lng

clay t 0-10% ...................................................................................................... 104


Hnh 3. 36: nh hin vi in t truyn qua (TEM) cho thy kch thc ht nano

bc t 4-7 nm ....................................................................................................... 106

Hnh 3. 37: B mt nanocomposite Ag/PLA xc nh bng AFM....................... 107

Hnh 3. 38:. Hiu sut dit khun ca vt liu PLA-bc nano i vi cc chng vi

sinh vt khc nhau. .............................................................................................. 108

Hnh 3. 39: Nng nano bc cn thit dit 100% vi khun th nghim: Nano

bc dng t do (ct mu xanh, bn tri), Nano bc trong PLA (ct mu nu,

bn phi). ............................................................................................................. 109


LI CM N

Trn thc t khng c s thnh cng no m khng gn lin vi nhng s h tr,

gip d t hay nhiu, d trc tip hay gin tip ca ngi khc. Trong sut thi gian

bt u lm lun vn cho n nay, em nhn c rt nhiu s quan tm, gip ca

qu Thy C, gia nh v bn b.

Vi lng bit n su sc nht, em xin gi ti qu Thy C khoa ha hc, trng i

hc Khoa hc T nhin H Ni, cng vi tr thc v tm huyt ca mnh truyn

t vn khin thc qu bu cho chng em trong sut thi gian hc tp ti trng. Em

xin gi li cm n chn thnh ti GS.TS. Nguyn c Ngha v cc bn ng nghip

phng Pht trin Cng ngh Ha hc v Phng polyme chc nng v vt liu nano. V

c bit em xin chn thnh cm n Ts. Hong Mai H v TS. Trn Mnh Tr tn

tm hng dn em hon thnh bi lun vn ny. Trong sut qu trnh thc hin lun

vn, khng th trnh khi nhng sai st. Do vy, em rt mong nhn c nhng kin

ng gp qu bu ca qu Thy C v cc bn kha lun ca em c hon thin

hn.

Em xin chn thnh cm n.


M U

Vit Nam l mt nc nng nghip ng th hai trn th gii v xut khu la go.

Hng nm nc ta sn xut khong 44 triu tn la go. Cng vi chng ta nhn

c khong 40 triu tn rm r. Ngy nay, khi nn kinh t ang ngy cng pht trin,

cc nhin liu ha thch c s dng rng ri th nhng ngun ph liu nng nghip

nh rm r khng cn l ngun cht t, ngun thc n chn nui chnh na. Ngun

ph liu ny ch yu c ngi dn t b sau mi v thu hoch. iu gy

nhim mi trng trm trng, lm nh hng n sc khe ca con ngi c bit l

ngi gi v tr em.

Trong sut th k qua, th k ca thi i nha, vt liu polyme ng vai tr

quan trng trong cc ngnh sn xut cng nghip, nng nghip v tiu dng. Nhng

ph thi ca vt liu ny gy nhim trm trng trong mi trng, bi kh nng phn

hy ca n trong thi gian rt lu, c loi n hng ngn nm.

khc phc nhc im ny, th gii hin nay tp trung pht trin cc loi vt liu

xanh, ngun gc sinh hc, c kh nng t phn hy, ti sinh v thn thin vi mi

trng, thay th cc loi polyme c ngun gc du m. Cc nghin cu nhm to ra

cc loi vt liu c kh nng phn hy sinh hc v thn thin vi mi trng ang thu

ht nhiu nhm nghin cu. Trong , xu hng s dng cc loi vt liu c ngun

gc t thin nhin dn thay th cc vt liu c ngun gc t du m ang ngy cng

c quan tm. Nhng loi vt liu xanh, vt liu ti to c kh nng phn hy sinh

hc, nh poly-axit lactic (PLA), Polyhydroxylbutyrat (PHB) c xem l cc ng c

vin cho hng pht trin ny. Trong , so vi cc polyme sinh hc khc, PLA c mt

s u im ni tri sau:

- Monome axit lactic c to ra bi qu trnh ln men cc sn phm t nng nghip

nn c th ti sinh.


- Tc ng tch cc n chu trnh CO2 do s dng thc vt lm nguyn liu.

- Tit kim nng lng.

- C th ti sinh PLA thnh axit lactic thng qua thy phn.

Chnh v nhng u im trn m PLA c xem l s la chn hng u trong cc

polyme sinh hc c kh nng thay th cc loi polyme du m. Hin nay, mt s loi sn

phm nha sinh hc da trn PLA ra i nh BiotaTM - Chai ng nc bng nha

PLA, NobleTM - Bnh ng nc hoa qu bng nha PLA, DannonTM , cc sn phm

thc phm chc nng s dng axit L-lactic, ngoi ra PLA cn c s dng trong cc

ngnh cng nghip v vt liu y-sinh...

Tip bc nhng nghin cu v PLA, chng ti ch to thnh cng PLA t phn

hy sinh hc t cc ngun ph liu nng nghip nh rm r. Quy trnh tng hp v cu

trc, tnh cht ca PLA c nghin cu k lng. Vt liu t hp ca PLA vi

polyethylene glycol, nano clay, nano bc cng c ch to v nghin cu hnh thi,

cu trc v cc tnh cht c trng.


1

Chng 1: TNG QUAN

1.1. Tng hp PLA t rm r 1.1.1. Ngun rm r ph liu Vit Nam

1.1.1.1. Tr lng rm r v phn b

Vit Nam l mt nc nng nghip vi tng din tch t dnh cho nng nghip

chim ti 35%, v khong 70% dn s lm nng nghip [1]. Trong la go c

xem l loi cy trng v ma v quan trng nht nc ta. Nng sut la go bnh

qun cng tng lin tc trong nhng nm qua t 4.2 triu tn/ha vo nm 2000 ln

5.3 tn/ha vo nm 2010. Nm 2014, theo s liu c tnh nng sut c th t mc

cao nht t trc ti nay l 5.7 tn/ha [2]. T nm 1990 n nay, sn lng la ca

Vit Nam lin tc tng trng nh ci tin cc k thut canh tc, tng nng sut cy

trng v mt phn nh m rng din tch canh tc hng nm.

Rm r l loi ph liu chnh trong qu trnh sn xut la go. Nhng kt qu cho

thy mi tn la thu c s cho tng ng 1.0 1.3 tn rm r trn ng rung ty

theo cng ngh thu hoch v iu kin x l, thu gom. T sn lng la go thu

c hng nm trn, ta c th tnh c sn lng rm r sau thu hoch ti nc

ta nm trong khong t 40 50 triu tn [20]. y c th c coi l ngun sinh

khi ln nu c thu gom v s dng mt cch hp l.

V mt phn b, nc ta hai khu vc cho sn lng rm r chnh l ng

bng sng Cu Long v ng bng sng Hng. Hnh 1.1 biu din s lng c th

v sn lng ca cc vng trong c nc. Theo , ng bng sng Cu Long v

ng bng sng Hng ln lt sn xut ra 52,5 v 16,8% sn lng ca c nc.

Cc khu vc khc thng l gieo trng nh l v c t l khng chim qu 9% [4].


2

Hnh 1. 1: Sn lng rm r ti cc khu vc trong c nc (2010)

Vi tr lng di do, nc ta c li th ln v ngun sinh khi t rm r

phc v cho pht trin cc hng nghin cu ti s dng chng cho hiu qu kinh t

cao. Chnh v vy chng ti nghin cu s dng ngun ph phm ny lm ngun

nguyn liu s dng cho mc ch ch to nha t phn hy sinh hc poly-axit

lactic.

1.1.1.2. Thc trng s dng rm r nc ta.

T xa xa, sau khi thu hoch xong, rm r c phi kh, thu gom v cht ng.

Rm r c s dng cho nhiu mc ch khc nhau nh lm cht t, lm thc n

cho gia sc (tru, b), sn xut nm rm, phn hu c vi sinh v lm vt liu xy

dng...

Ngy nay, khi ngnh cng nghip ang ngy cng pht trin, i sng ca ngi

dn c nng ln. Ngun nguyn liu du m, kh t v than pht trin th

ngi nng dn khng s dng rm r vo nhng mc ch trn m hu ht b t

b ti ng rung, va cng vn chuyn, va lm tng cht mu cho t. Tuy

nhin, vic t b ny gy lng ph v lm nhim mi trng v gy hi trc tip

ti sc khe ca ngi dn. Theo cc chuyn gia y t, m bi tro t rm r gy ra


3

(c bit vo thng 6/2009 ti H Ni) gy nhim khng kh, rt c hi i vi

sc khe con ngi, nht l i vi tr em, ngi gi v ngi mc bnh ng h

hp.

1.1.2. Axit lactic

Axit lactic (acid 2-hydroxypropionic) hay cn gi l axit sa l axit tn ti rng

ri trong t nhin, c tm thy ngi, ng vt, thc vt v vi sinh vt. N ln

u tin c pht hin bi nh ha hc Thy in Carl Wilhelm Scheele vo nm

1780 trong sa chua. Axit lactic c chp nhn l mt sn phm ca qu trnh

ln men vo nm 1847 [5]. C cng thc ha hc l CH3CHOHCOOH, l mt axit

hu c c 3 Carbon: trong , mt nguyn t carbon nm trong nhm carboxyl, mt

nguyn t nm trong nhm methyl CH3 v mt nguyn t gia c cha nhm

hydroxyl (hnh 1.2). Axit lactic khan tinh khit l nhng ht tinh th rn mu trng

c nhit nng chy thp. i lp vi cc axit khc, axit lactic khng bay hi,

khng mi, khng mu v c v axit trung bnh. Hm lng carbon, hydrogen, v

oxygen trong phn t tng ng l 40%, 6.71% v 53.29% [5].

Hnh 1. 2: Cng thc cu to ca axit lactic

Trong cng thc cu to phn t ca axit lactic c mt carbon bt i nn chng

c hai ng phn quang hc l axit D-lactic v axit L-lactic. Hai ng phn quang

hc ny c tnh cht ha l ging nhau, ch khc nhau kh nng lm quay mt


4

phng phn cc nh sng, mt sang phi v mt sang tri. Do tnh cht sinh hc

ca chng hon ton khc nhau [7].

Hnh 1. 3: Cng thc cu to ca hai ng phn axit lactic: axit L(+)-lactic

tri, axit D(-)-lactic phi

Axit L(+)-lactic c chuyn ha hon ton v nhanh chng trong qu trnh tng

hp glycogen. Axit L-lactic dng tinh th, chng c kh nng tan trong nc, tan

trong cn, tan trong ether, khng tan trong CHCl3, nhit nng chy 28C [7].

Axit D(-)-lactic c chuyn ha t hn v phn khng chuyn ha s c bi

tit di dng urein. S hin din ca axit khng c chuyn ha trong ng tiu

ha s gy tnh trng nhim axit trong tr s sinh. Axit D- lactic dng tinh th, tan

trong nc, tan trong cn, nhit nng chy 28C [7].

Nu axit D-lactic v axit L-lactic c trong mt hn hp theo t l 50:50 ngi ta

gi l hn hp raxemic. Hn hp ny c k hiu l axit D/L-lactic. Tuy nhin

trong qu trnh ln men khng c hn hp c t l l tng ny m ta ch c th thu

c khi tin hnh tng hp hu c [7]. Axit D/L lactic l dch lng dng tinh th,

tan trong nc, cn, khng tan trong chloromethane (CH3Cl), nhit nng chy

16,8C, nhit si 122C [7]. Axit lactic c khi lng phn t l 98.08, khng

mu, c mi nh.

Hai dng ng phn quang hc ny c tnh cht vt l khc nhau. Cc nhm

hydroxyl v carboxyl ca axit lactic cho php axit lactic c mt khong rng cc

phn ng ha hc. Axit lactic c pKa khong 3.86 25oC. N l mt axit trung bnh

c th phn ng vi cc kim loi hot ng to kh hydro v mui kim loi. Axit

lactic phn ng vi mui cyanide to thnh kh hydro xyanua, phn ng vi mui


5

diazo, dithiocarbanate, isocyanate, mercaptan, nitrit, sulfit, thiosulfate, sulfua

dioxide (SO2), carbonate to kh c hoc d chy. Axit lactic c th to thnh

dilactide qua phn ng ester ha vi ru v chng ct xc tc, to ra glycol bng

phn ng hydrogenolysis v to ester lactate bng phn ng kh nc xc tc [5].

T nhng phn ng trn, axit lactic c nhiu ng dng trong cng nghip v sn

xut. Mt vi tnh cht vt l v ha hc ca axit lactic c trnh by trong bng

sau:

Bng 1. 1: Tnh cht vt l v ha hc ca axit lactic

Tnh cht D-lactic L-lactic D,L-lactic TL tham kho

Khi lng phn t 90,08 90,08 90,08 [5]

Nhit nng chy (oC) 52,8 53,0 16,8 [5]

Nhit si (oC) 103 122 [7]

Hng s phn ly Ka 25oC 1,90*10-4 1,38*10-4 [7]

pKa 25oC 3,83 3,79 3,73 [5]

Quay quang hc -2,5 +2,5 [7]

1.1.3. Qu trnh ln men tng hp axit lactic t rm r.

Cc vi khun lactic c chia lm hai nhm tu theo cch ln men ng ca

chng: cc vi khun lactic ln men ng hnh v cc vi khun lactic ln men d

hnh. Nhiu tc gi chng minh rng vic xc nh cc sn phm ln men cui

cng ca vi khun lactic ph thuc rt nhiu yu t (pH, CO2, O2, trng thi sinh l

ca t bo) [22]:

- Ln men ng hnh (Homofermentation) l qu trnh ln men trong sn

phm ch yu l axit lactic. Qu trnh ln men xy ra theo con ng Embden -

Meyerhof Parnas [22]. Hiu sut gn nh 100%. Qu trnh ln men ng hnh ch

trao i nng lng, vi khun khng s dng glucose xy dng t bo m ch s


6

dng axit lactic ca c cht. Chnh v th m khi phn lp hay nui cy vi khun

lactic cn lng cao tht, cao men v pepton tng i nhiu.

- Ln men d hnh (Heterofermentation) l qu trnh ln men trong ngoi cc

sn phm l axit lactic th cn c nhiu sn phm khc nh l acetic acid

(CH3COOH), malic (HOOC-CH2-CH(OH)-COOH), formic (HCOOH), furmaric

(HOOC-CH=CH-COOH), ethanol, carbondioxide v manitol (C6H14O6) [22].

Thng thng khong 50% ng b chuyn thnh cc sn phm ph ny. Trong

qu trnh ln men ny cc vi khun khng s dng theo ng EMP do thiu enzym

fructose-bisphosphate-andolaza v tri-P-isomeraza m phn gii glucoza qua con

ng pento-phosphate oxi ha (PPO).

Trong mt s trng hp, ln men ng hnh c th c chuyn sang dng d

hnh khi cc iu kin ln men thay i. Ln men lactic ng hnh c biu din

bng phng trnh:

Tuy nhin khng bao gi t c 100% s chuyn ha. Nu mt qu trnh ln

men t hiu sut 80% axit lactic th c coi l qu trnh ln men ng hnh. Trong

ln men d hnh, cc sn phm ph v axit lactic c sinh ra vi khi lng phn

t gam nh nhau [18]. S chuyn ha tm tt qu trnh ln men ng glucose

ca vi khun lactic c m t tm tt nh hnh sau:


7

Hnh 1. 4: S qu trnh ln men ng glucose vi khun lactic.

1.1.4. Lactide

Lactide (3,6- dimethyl 1,4- dioxane 2,5-dione) l mt dime vng vi monome l

axit lactic. Do c hai nguyn t carbon bt i xng trong phn t nn lactide tn

ti ba dng khc nhau (hnh 1.5).


8

D-lactide L-lactide Meso-lactide

Hnh 1. 5: Ba cu trc ca lactide

Tnh cht vt l ca lactide c dn ra trong bng 1.2

Bng 1. 2: Tnh cht vt l ca lactide

Tnh cht n v D-lactide L-lactide Meso-lactide

Khi lng phn t g/mol 144,12 144,12 144,12

Nhit nng chy oC 96-97 96 53

Nhit si oC oC 255

Nhit nng chy J/g 146 128

Nhit bay hi kJ/mol 63

Mt rn g/ml 1,32-1,38 1,32-1,38

nht lng mPa.s

2,71(110oC);

2,23 (120oC);

1,88 (130oC)

Gc quay quang hc +260 -260

1.1.5. Poly-axit lactic (PLA)

Poly-axit lactic (PLA)/ polylactide l mt loi polyme nhit do bn tinh th,

gin v rn, c nhit thy tinh ha tng i thp (~600C) v c nhit nng


9

chy 175 -180oC. PLA ang l i tng c quan tm v pht trin nhiu nht

trn th gii bi d dng c gia cng trong cc thit b gia cng cht do thng

thng v cng d dng phn hy sinh hc, thch hp ch to bao b, mng bc

thc phm, cc sn phm s dng mt ln. Cc tnh cht ca nhng polyme t axit

lactic bin i trong mt khong rng ph thuc vo t l v s c mt ca hai ng

phn quang hc D,L-lactic hoc cc thnh phn khc [7].

Bng 1. 3: Kh nng phn hy sinh hc ca mt s polyme

Tn Polyme c tnh

Bio-PE C ngun gc sinh hc

Bio-PP C ngun gc sinh hc

Bio-PVC C ngun gc sinh hc

Bio-PC C ngun gc sinh hc

PET Phn hy sinh hc

PLA C ngun gc sinh hc, phn hy sinh hc, tng hp

sinh hc

PA Phn hy sinh hc v tng hp sinh hc

Starch blends C ngun gc sinh hc cc b, phn hy sinh hc cc b.

Regenerated cellulose C ngun gc sinh hc, phn hy sinh hc

Bio-PMMA C ngun gc sinh hc

Tuy thi gian pht trin cha lu (khong trn 10 nm) nhng ch ring ti

chu u, tc pht trin ca cc sn phm nha phn hy sinh hc tng gp 10

ln, cho thy tim nng chim lnh th trng rt ln. Mt s sn phm thng mi

c mt s cng ty a ra th trng nh cng ty Mater-B vi sn phm ti


10

xch v dng c n ung t hy sau vi ln s dng. Cng ty Vegemat vi dng c

mc pht bng trong mn nh golf, s dng PLA trong thnh phn a DVD, inh

t tiu c nh xng trong y t

Hnh 1.6 l mt s ng dng ca poly-axit lactic c lu hnh trn th

gii.

NG DNG PLA

Vi si PLA

Thuc nano Vt dng v VL cng nhip

Bao b thc phm

Hnh 1. 6: Mt s sn phm c s dng nha phn hy sinh hc PLA

PLA c th sn xut t axit lactic vi nhiu phng php khc nhau (hnh 1.7). Tuy

nhin, PLA c khi lng phn t cao th c ch to ch yu bng phng php

trng hp m vng dime dilactide, l sn phm ca phn ng kh trng hp axit

lactic. Phng php ny phi tri qua hai giai on v bc tinh ch. Do , chi ph

tng ln ng k. Nhiu kin cho rng phn ng ngng t tch nc trc tip

tng hp PLA khi lng phn t cao khng th tin hnh c do s cn bng

phn ng khng h tr mt polyme khi lng phn t cao. PLA c tng hp t


11

phn ng a t c khi lng phn t thp, tnh cht c l km v do khng c

nhiu ng dng. V th nhiu nghin cu c tp trung gii quyt vn ny

bi v s cn thit ca vic sn xut polyme c khi lng phn t cao vi chi ph

thp.

Hnh 1. 7: Cc phng php tng hp PLA t axit lactic

1.1.6. Tng hp PLA 1.1.6.1. Tng hp lactide

Tng hp poly-axit lactic c thc hin bng phn ng trng hp m vng

lactide (ROP). Lactide l mt dime vng vi monome l axit lactic. Phn ng to


12

lactide tri qua hai giai on. u tin, monome axit lactic c trng ngng to

thnh oligome. Sau oligome tri qua qu trnh polyme ha ng thi vng

ha to thnh lactide. Qu trnh to thnh lactide l mt trong nhng giai on quan

trng nht do bi tinh khit quang hc ca lactide c nh hng n sn phm

polyme nhn c.

Nm 1845, Pelouze tng hp thnh cng lactide bng phn ng ester ha

loi b nc v thu c tin polyme. Sau ng tip tc gia nhit v cho hi lu

dng sn phm th nhn c cc ht tinh th v t tn l lactide [8].

Nm 1914, Gruter v Pohl a ra mt phng php ci tin tng hp

lactide. ng pht hin rng axit lactic t ester ha nhit khong 120 135oC.

Sau khi loi b nc hon ton, ng cho thm km oxide vo vi vai tr l cht xc

tc, khi lactide c ct ra trong iu kin chn khng nhit 200oC. Mt

bc tin mi l s dng thic lm cht xc tc. y l loi xc tc ph bin

trong phn ng trng hp. S quy trnh tng hp v tinh ch lactide c trnh

by trong hnh 1.8.

Hnh 1. 8: S minh ha quy trnh tng hp lactide bng phng php trng

hp oligome axit lactic.


13

Bc 1: Phn ng ngng t

Bc 2: Phn ng unzipping

Hnh 1. 9: Cc bc trong qu trnh tng hp L-Lactide

Bc u tin l s ngng t trc tip axit lactic thnh oligome thng qua qu

trnh loi nc, gia nhit trong iu kin chn khng m khng cn s dng xc tc.

Thng thng oligome nm trong khong 500 - 2000 Da. Bc tip theo l phn

ng unzipping nhit. Xc tc cho phn ng l cc kim loi, oxit kim loi. Nhit

nm trong khong 200 - 300oC, trong iu kin chn khng. Sn phm lactide th

thng c kt tinh li trong dung mi hoc h dung mi ph hp loi b cc

tp cht (hnh 1.9).

C ch ca phn ng to lactide t oligome gi l phn ng back - bitting ca

nhm OH cui mch oligome (hnh 1.10). Nguyn t carbon ca nhm carbonyl

trong oligome mang mt phn in tch dng do tng tc vi xc tc nn b tn

cng bi nhm OH ny. di mch oligome b ct ngn li khi to thnh lactide.


14

HOHC

CH3

C

O

OHC

CH3

C

O

OHC

CH3

C

O

OH

n-2

CH C

O

OHC

CH3

C

O

OHH3C

OC

HC

OH

CH3O

n

O

O

O

O

H3C

H

CH3

H HOHC

CH3

C

O

OHC

CH3

C

O

OHC

CH3

C

O

OH

n-4

Hnh 1. 10: Qu trnh back - bitting to lactide

Cc yu t nh hng n qu trnh to chn khng trong vic tng hp lactide

khng dung mi bao gm:

- Nhit : nhit phn ng tng lm tng tc phn ng, p sut hi ca

lactide trong hn hp cng tng theo, do tc phn ng raxemic ha cng tng

theo.

- p sut: s dng p sut nh hn hoc bng 10 mbar, p sut ln hn 10

mbar, ng lc cho s bay hi lactide thp, tc phn ng gim.

- Nng xc tc: tc phn ng tng theo nng cht xc tc. Trong thc

t, nh hng ny khng tuyn tnh do ng hc trong thit b ng vai tr quan

trng ch yu.

- S raxemic: s hnh thnh cc ng phn i quang ca axit lactic khc v

meso - lactide l khng mong mun trong qu trnh sn xut lactide tinh khit.

Nhit cng cao, thi gian phn ng cng di v nng xc tc cao s lm tng

tc raxemic [9]. S nh hng ca nhit v xc tc ln tc hnh thnh

lactide cng nh s kim sot tc raxemic c th tr nn kh phc tp.


15

- Cc tp cht: cc cation kim loi nh K, Na trong phn ng lm tng s

raxemic ha, trong khi cc kim loi khc nh Al, Fe li ng vai tr l cht xc tc

cho phn ng ester ha hnh thnh polylactide [9]. Cc kim loi ny c th b loi

b trong cn thng qua qu trnh n mn. Mt vi tc gi nghin cu s c mt

ca cc axit trong qu trnh phn ng. Cc axit ln men mono v dicarboxylic lm

mt cn bng trong phn ng ngng t axit lactic. Do , thnh phn ca chui

oligome axit lactic thu c c th khng ging PLA tinh khit do s kh trng hp

xc tc khng hon ton v b cn tr ca oligome thnh lactide.

Trong sn xut PLA, phn ng phn hy ng vai tr quan trng ch yu thng

qua s ct mch chui ni phn t v iu ny c th gy nh hng n s tng

hp lactide.

1.1.6.2. Tinh ch lactide

Phn ng tng hp lactide to sn phm hi lactide th cha axit lactide, oligome

axit lactide, nc, meso-lactide v cc hp cht khc. tinh ch lactide chng ta

thng s dng hai phng php chnh l chng ct v kt tinh.

- Chng ct: tch hn hp gm hai phn nh lactide, nc, axit lactic v oligome

ca axit lactic thnh nhng phn ring i hi s hiu bit ng hc v hot ng

ca thit b chn khng. Sn phm chng ct v sn phm cn li y c th c

ti ch nhng s kt t ca cc tp cht t bnh phn ng hoc s to thnh meso-

lactide trong sut qu trnh i hi s iu chnh nhit v thi gian cn thn.

Nm 1993, Gruber m t r rng s chng ct lactide [11]. Lactide th t phn ng

tng hp c chng ct trong mt ct th nht chuyn axit v nc, sau

meso - lactide c tch t lactide trong ct th hai. Khi im si ca cc hp cht

trong khong 200 - 300oC, phn ng tin hnh p sut thp. Bi v, s khc nhau

nhit si ca lactide v meso - lactide th kh nh, do khi chng ct i hi

nhiu a l thuyt (>30). Thit b chng ct Cargill/Nature Works s dng mt lot

cc ct ct lin tc [11].


16

- Kt tinh trong dung mi: y l phng php ph bin c s dng trong

phng th nghim tinh ch lactide. Kt tinh lactide t hn hp toluene v ethyl

acetate [11] thu c lactide c tinh khit cao.

- Kt tinh nng chy: tinh th lactide d dng c kt tinh, tuy nhin thu

c hiu sut cao trong qu trnh tinh ch lactide i hi phi c nhng thng tin

nh gi cc thnh phn axit lactic , oligome, meso-lactide v nc nh nhit ng

hc, s cn bng ca t l axit lactide/ lactic v h lactide/ meso - lactide.

Phng php kt tinh cho lactide c tinh khit cao, ph hp tng hp axit

poly-L-lactic (PLLA) ng nht c khi lng phn t cao. Phng php chng

ct i hi s a l thuyt ln, ngoi ra cn c th xy ra s polyme ha ca lactide

trong ct ct. Qu trnh kt tinh p dng loi meso - lactide ra khi sn phm.

Tuy nhin, hiu sut thu hi D,L-lactide khng cao do bi qu trnh kt tinh li cn

lp li vi ln m bo tinh khit.

Gn y, rt nhiu phng php c p dng thu hi lactide tinh khit.

Trong , nc c s dng nh l mi trng tch D,L-lactide v meso-

lactide da trn tan khc nhau. D,L-lactide tan trong 100 g nc vi tc 0,5 -

0,6 g/h 20oC v 4-5 g/h 60oC, trong khi 10 g meso - lactide tan trong 100 g nc

trong 1 pht cng iu kin. V vy, meso - lactide c th c loi b khi

lactide th khi ha tan vo nc. Qu trnh polyme ha oligome cng quan trng

nh qu trnh tch lactide khi oligome PLA. Tuy nhin, cha c bo co no m t

chi tit qu trnh tch lactide tinh khit quang hc t qu trnh polyme ha

oligome PLA.

1.1.6.3. Tng hp PLA

Poly-axit lactic l mt polyester c tng hp bng phn ng ngng t monome

(axit lactic) hoc trng hp m vng lactide. Qu trnh trng ngng to sn phm

ph l nc v rt kh b tch ra khi hn hp nn gii hn khi lng phn t ca

polyme. Phn ng trng hp m vng (ROP) lactide c th cho khi lng phn t


17

polyme ln hn nhiu v l phng php c s dng nhiu nht. T quan im

ng hc, lactide l mt trong nhng vng 6 cnh c th polyme ha. Entanpy

trng thi tiu chun polyme ha tng i ln (-23kJ/mol). Da trn d liu tinh

th hc tia X, trong phn t tn ti sc cng vng do c cha 2 nhm ester trong

mt vng phng. Tuy nhin, sc cng ny l lc nh hng cho qu trnh phn ng

m vng trng hp. trng hp (DP) t nht cng t l vi thi gian chuyn ha

monome, t l mol monome trn cht khi mo (v d tng hp block copolyme)

cng nh ct mch chui polyme. Qu trnh phn ng m vng trng hp lactide

yu cu nhng xc tc ph hp phn ng xy ra v thu c polyme c tnh cht

mong mun.

a) Tng hp PLA bng phn ng trng hp m vng.

Phn ng trng hp lacton thng thng c tin hnh dng khi hoc dung

dch (THF, toluene, chloroform), nh tng hoc huyn ph. Trong phn ng

trng hp dng khi thng thng c nhit khong 100 - 150oC, dng dung

dch thng s dng nhit thp hn khong 0 - 25oC lm gim ti thiu cc

phn ng ph. Lactide raxemic c polyme ha s dng cc cht khi mo cha

Zn, Al. Ba nhm cht khi mo gy nh hng nh ZnCl2 c hot ng chuyn ha

mnh nht, ZnEt2 v ZnEt2/Al(OiPr)3 c hot ng trung bnh v Al(acac)3 khng

hot ng. C ch ca phn ng trng hp ph thuc vo loi phn ng. Ba c ch

phn ng chnh l cationic, anionic v phi tr - b sung. Tuy nhin, polyester khi

lng phn t cao ch thu c bng cch s dng phn ng trng hp anionic hoc

phi tr - b sung.

b) Trng hp m vng cationic.

Trng hp m vng cationic hnh thnh cc ion mang in tch dng ri sau

b gn vo mt monome. Cc ion ny tch in dng l nh qu trnh SN2. Phn

ng trng hp m vng cationic ca lactic t c bng cch s dng cc tc nhn

alkyl, acyl, axit lewic v protic.


18

Methyl triflate (MeOTf) c pht hin l mt cht khi mo hiu qu cho phn

ng trng hp m vng L-lactide. Cc phn ng c thc hin trong nitrobenzene

trong 48h nhit ti u l 50oC to ra cc ui methyl ester. Qu trnh trng hp

xy ra do s tch lin kt alkyl - oxygen d hn l lin kt acyl - oxygen. Theo gi

thit , phn ng pht trin thng qua s hot ha ca monome bi qu trnh metyl

ha v vi methyl triflate bi s tn cng SN2 ca anion triflate trn vng lactide

mang in tch dng vi s nghch o ca ho hc lp th. Gi thit rng phn

ng ny c bt u t s tn cng nucleophile vo lactide v tr cui ca chui

cation c hot ha vi s o ngc mch dn n s duy tr cu hnh. S

chuyn di lin kt alkyl - oxygen dn n phn ng trng hp (hnh 1.11)

Hnh 1. 11: C ch trng hp m vng cation lactide


19

Atthoff v cc ng nghip tin hnh trng hp khi m vng lactide 130oC

s dng 5% mol diphenylammonitriflate (DPAT) nh mt cht khi mo axit -

proton trong ethanol. Di cc iu kin c th to ra c PLA c khi lng

phn t ln n 12000 g/mol vi phn tn 1,24 v 1,51 trong 4 ngy.

c) Trng hp m vng anionic.

Cc cht khi mo hiu qu cho phn ng trng hp anion l cc kim loi kim,

oxit kim loi kim, phc naphthalen kim loi kim vi u ether... S tn cng

nucleophile ca cht khi mo tch in m ln carbon ca nhm carboxyl hoc ln

alkyl - oxygen lm khi mo phn ng, hnh thnh polyester mch thng. S trng

hp - lactone bt u thng qua s tch alkyl - oxygen hoc acyl - oxygen vo

nhm cui ca carboxylate v alkoxide (hnh 1.12)

Hnh 1. 12: S khi mo ca phn ng trng hp m vng lactone

Trong lactone ln hn, nh caprolactone hoc lactide, phn ng thng bt u

bng s phn chia acyl - oxygen dn n s hnh thnh mt ion alkoxide hnh (hnh

1.13)


20

(a)

(b)

Hnh 1. 13: Trng hp anionic ca (a) lactone, (b) lactide

d) Trng hp m vng phi tr - b sung


21

Trng hp phi tr - b sung c s dng rng ri tng hp cc polyester bo

vi cu trc c nh r. Cc cht khi mo c s dng rng ri nht l cc oxit

nhm, oxit thic v carboxylate. Oxit kim loi lin kt cng ha tr hoc carboxylate

vi obitan dcha lin kt hot ng nh cc cht khi mo phi tr. Khng ging

vi cc cht khi mo anionic trong cc phn ng trng hp, cc cht khi mo ny

c th to ra polyme lp th c MWD nh v kim sot c khi lng phn t

vi cc nhm cui c xc nh r. Cc carboxylate c i lc yu hn so vi cc

oxit. Phn ng trng hp c bt u thng qua s phn chia acyl - oxygen ca

lactone vi s b sung ca monomer trong lin kt kim loi - oxi ca cht khi

mo. S phi tr ca oxi ngoi vng vi kim loi dn n s phn cc ha v to ra

carbon carbonyl ca monomer nhy hn s tn cng ca nucleophile (hnh 1.14).

(a)

(b)

Hnh 1. 14: C ch phi tr b sung ca trng hp lactone (a) v lactide (b)


22

Kricheldorf (2000) tin hnh ly thic (II) 2-ethylhexanoate un nng ln trn

100oC to thnh axit octanoic. Axit c gii phng ra c th ester ha vi ru

to ra nc, c th phn ng vi Sn(Oct)2 hnh thnh thic oxide v thic

hydroxide. Di cc iu kin , kh c th kim sot c khi lng phn t v

cc phn ng ph bi s c mt ca nc hoc cc hp cht hydroxyl khc ging

nh khi mo phn ng trng hp. Kh nng phn ng tng i ca cc cht

khi mo l alcoxide kim loi i vi phn ng ester ha ph thuc vo kim loi v

aluminum ankoxit c kh nng phn ng thp nht.

Thic octoate l cht khi mo c s dng rng ri nht bi v tc phn ng

cao, c kh nng ha tan trong monome tan chy v kh nng to sn phm

polylactide khi lng phn t cao. S thm vo mt lng xc nh ca cht nn

Lewis nh triphenylphosphine trong axit 2 - ethylhexanoic lm tng ng k tc

trng hp lactide. Triphenylphosphine c hai nh hng tt: n lm tng tc

trng hp v tr hon s xut hin ca cc phn ng back bitting ti thi im t l

monome/cht khi mo ln hn hoc bng 5000.

Engel (1997) nghin cu phn ng trng hp m vng lactide vi s c mt

ca Sn(Oct)2. ng th nghim li di cc iu kin thch hp. S hnh thnh

ca mt sn phm ph, hydroxy tin (II) lactate khi mo phn ng trng hp v

t c sn phm khi lng phn t cao. Tuy nhin, phn ng trng hp vi

Sn(Oct)2 nhanh hn vi hydroxy tin (II) lactate.

Schwach (1998) cho rng phn ng trng hp th nhy vi m, v ch c s

dng km l hiu qu. Mt lng nh ca mt sn phm ph c cho l km

lactat. Hp cht ny xut hin c vai tr l mt cht khi mo hiu qu ca phn

ng trng hp m vng. S khi mo bi km lactat cho polyme c khi lng

phn t cao vi chuyn ha v tc trng hp cao.


23

Kleawkla (2005) tho lun v c ch phi tr - b sung ca phn ng trng

hp m vng ester. Ban u, n c cho rng, Sn(Oct)2 l cht khi mo nhng

iu ny sau b bc b bi thc t rng khi lng polyme khng ph thuc vo

t l mol ca monome: Sn(Oct)2.

Vai tr ca xc tc v cht khi mo trong phn ng trng hp Lactide

Nhiu tc gi nghin cu c ch phn ng trng hp m vng s dng xc tc

Sn(Oct)2 nhng khng c l thuyt gii thch cc kt qu th nghim ca phn ng

trng hp phi tr - b sung [17]. Nhng c ch trng hp khc nhau ph thuc vo

iu kin trng hp, nng xc tc v cht khi mo v s c mt ca mt dung

mi.

y, gi thit rng, lactide c trng hp khi vi xc tc Sn(Oct)2 c ch

c a ra bi Kowalski [17]. Do lactide l mt ester vng, vng ca n c th

c m bng cch tn cng nucleophile ln lin kt ester bt u trng hp.

Cc cht khi mo ph hp (nucleophile) l nc v ru, nhng cht c nhm

OH. Mt lin kt ester ca vng lactide b ct t bi phn ng ca nhm OH ca

cht khi mo R-OH vi lactide, to ra mt nhm ester cui mch mi R-O-C(O)-

v mt nhm OH cui mch hnh 1.15

Hnh 1. 15: Trng hp m vng lactide vi cht khi mo l ru

Trong nhiu bi bo cho rng xc tc Sn l cht khi mo bi v lactide cng

trng hp khi c mt ca xc tc Sn v s nh hng ca cc tp cht b b qua.


24

Cht khi mo hoc ng khi mo l cht c th bt u phn ng trng hp, trong

trng hp m vng lactide, cht khi mo y phi l mt nucleophile khng

phi l xc tc Sn (gi nh ca Kowalski) ng cho rng Sn(Oct)2 cn hot ha vi

R-OH (Hnh 1.16) [17].

Sn(Oct)2 + ROH Oct-Sn-OR + OctH

Hnh 1. 16: S phn ng ca thic octonate vi cht khi mo l ru

hoc tp cht hnh thnh cht hot ng xc tc Sn-O-R

Tm li, nhng cht cha nhm OH nh cht khi mo R-OH v cc tp cht

axit lactic cho sn phm c khi lng phn t ln nht [9]. Tc trng hp c

kim sot bi cc nhn t nh nhit , xc tc vi ch rng xc tc thic (II) cn

cht khi mo tr nn hot ng hn.

Ru

Trong trng hp cht khi mo l nc th R chnh l H v s thy phn ca

lactide to thnh lactic lactoyl (HL2) axit kt hp vi lactide trong s c mt ca

xc tc trng hp to thnh PLA vi nhm hydroxyl v nhm carboxyl cui mch.

Nu nhm hydroxyl ca axit lactic hot ng nh mt cht khi mo, th thu

c PLA c mt nhm hydroxyl cui mch v nhm cui axit lactic (HOOC-

CH(CH3)-O-C(O)-).

Nu cht khi mo l cc polyme thin nhin nh polyethylene glycol (PEG),

lactide c th trng hp t nhm hydroxyl cui mch ca PEG to thnh copolyme

PEG/PLLA.

T l mol ca monome v cht khi mo (M/I) nh hng ch yu ti khi lng

phn t ca PLA. T l cao ca cht khi mo to ra cc chui polyme ngn, v

lng nh ca cht khi mo to ra polyme c khi lng phn t cao. Nhm

hydroxyl lm cht khi mo trong monolactide thp hn th trng hp cng cao


25

[17]. Do nc v axit lactic c th gy ra s ct vng ca lactide v bt u phn

ng trng hp, do , nc v axit lactic cn phi c loi b trc khi trng hp.

Axit carboxylic

Axit carboxylic t c s dng lm cht khi mo nhng chng gy cn tr

phn ng trng hp s dng xc tc Sn(II). Theo Kowalski, axit carboxylic c th

gim tc phn ng trng hp do chuyn s cn bng gia ROH v Sn(Oct)2

chuyn v pha to Sn(Oct)2 khng hot ng. V th, t khi lng phn t

mong mun cn ko di thi gian phn ng trng hp, tuy nhin thi gian phn ng

di nhit cao trong s c mt ca cht xc tc l tc nhn gy ra s phn hy

ca phn ng trng hp [5]. Nm 1993, OBrien cng cho rng, axit carboxylic lm

gim mnh tc ca phn ng trng hp [17].

Do , axit t do v nc l cn thit cho tng hp lactide, nhng lng tp cht

cha nhm hydroxyl cng t, th bn v tnh cht ca lactide cng tt.

Kim loi

Cc cation kim loi nh Sn, Zn, Fe, Al v Ti khng ch lm tng phn ng trng

hp, m cn nh hng n phn ng thy phn, oxy ha, racemic ha hoc cc

phn ng phn hy khc ca PLA v lactide [9]. Do , axit lactic c s dng

cho phn ng tng hp lactide nn c hm lng cation kim loi thp trnh s

racemic ha trong sut qu trnh tng hp lactide.

OBrien nghin cu s to mu en ca lactide nh l mt hm tng ng vi

s c mt ca Fe trong nguyn liu. Cc nghin cu khc cng chng minh rng

hm lng kim loi thp th rt ngn c thi gian phn ng trng hp.

Cc tp cht cation nh cc ion kim loi kim khng nh hng trc tip n tc

phn ng, nhng thnh phn kim loi kim c mi tng quan vi lng meso-

lactide trong lactide th [9].

tinh khit quang hc


26

tinh khit quang hc ca vt liu nh hng ti cc tnh cht ca vt liu nh

im nng chy, kh nng kt tinh v bn c hc [17]. tinh khit quang hc

ca monolactide cng ln th sn phm PLA thu c cng c tinh khit cng

cao.

Hm lng ng phn D-lactide cng nh hng n tnh cht ca polyme. PLA

nature Work Ingeo rt d c tng hp v c dng lm vt liu ng gi sinh

hc v nh hnh do lng meso-lactide ca n tng i cao. Nhng kh nng chu

nhit km (nhit lm thay i hnh dng thp) trong sut qu trnh vn chuyn v

ct gi. Meso-lactide cn phi loi b t L-lactide v D-lactide thu c polyme

c tinh khit quang hc cao.

Kolstand [17] nghin cu s kt tinh ca cc cht ng trng hp L-lactide v

meso - lactide. ng pht hin ra rng 1% meso-lactide hoc D-lactide lm im

nng chy ca PLA gim i 3oC. Vi 3% meso-lactide trong PLA th kt tinh s

chm hn 2 ln so vi PLLA di cng iu kin tng t. Vi 6% meso-lactide

trong PLA th kt tinh cn gim n 10 ln.

iu ny cho thy s cn thit ca vic gim lng meso-lactide trong hn hp

monome cho PLA bn tinh th bi v s hnh thnh ca meso-lactide t phn ng

racemic ha khng th trnh khi trong phn ng trng hp lactide. Theo Gruber v

cng s th s racemic ha c kim sot bi cc yu t nh nhit , p sut, thi

gian vi s c mt ca xc tc hoc cc tp cht, s lin quan nng ca hai i

quang trong sut qu trnh phn ng [7].

p ng cc nhu cu ng dng thc tin i hi PLA phi c kh nng chu

nhit cao, iu ny ph thuc vo tinh khit quang hc ca PLA, do yu cu

hm lng meso-lactide phi thp nht hay monome lactide c tinh khit quang

hc cao nht.

Tm li: nhng c tnh quan trng nht ca monome lactide l tnh axit, hm

lng nc, kim loi nng v tinh khit quang hc.


27

- Tnh axit: v d axit lactic hoc axit actoyl lm gim tc trng hp v hn

ch hiu qu trng hp, tnh axit ca lactide nn nh hn 10meq/kg v tt nht l

khng ln hn 5 meq/kg.

- Nc gy ra phn ng thy phn ca lactide v lm gim tnh cht ca PLA

- Ion kim loi: cc ion Sn, Zn, Fe v Al lm tng phn ng trng hp nhng cng

nh hng ti phn ng thy phn, oxy ha hoc cc phn ng phn hy khc.

Cation kim c th gy s raxemic ha thm ch lng ppm.

- tinh khit quang hc: monome lactide c tinh khit quang hc cng cao,

sn phm PLA thu c cng lm tng tinh khit quang hc cao, iu ny kim

sot c cc tnh cht vt liu nh tan chy, s kt tinh v bn c hc.

1.2. c trng cu trc ca PLA 1.2.1. Vi cu trc, hnh thi hc v hnh dng.

Vi cu trc v hnh thi hc ca poly(axit L-lactic) thng phn nh v cho thy

nhng thay i trong thnh phn polyme. iu ny l do nhng kiu khc nhau ca

phn ng phn hy, tng tc hoc tnh khng trn hp gia cc thnh phn trong

phi trn. PLA c ng dng rng ri v c khuynh hng chu nh hng ca

nhng phng php gia cng khc nhau v mi trng bo qun khc nhau. V th,

nhiu phng php phn tch vi cu trc v hnh thi hc ca PLA c pht

trin. Phng php knh hin vi in t qut (SEM) v knh hin vi lc nguyn t

(AFM) l nhng phng php in hnh nghin cu hnh thi hc v tng tc

ca PLA hay gia PLA v cht n, hoc cht gia cng trong phi trn hoc

composite [10]. Nhng tnh cht hnh thi hc v hnh dng ca PLA thng c

nghin cu bng ph 1H-NMR hoc ph dao ng. Ph Raman hoc ph hng

ngoi (IR). Ph IR v Raman thng c s dng nhn c thng tin v pha

tinh th v v nh hnh ca PLA [10]. T thng tin trn ph Raman v so snh vi

d liu v tng hp polyme c th phn tch r hn v mm do ca chui

polyme. Trn di Raman ti 1044 cm-1 c trng cho cng lin kt C-C v dao


28

ng ca lin kt C-H. Di ti 1128 cm-1 c trng cho cng lin kt O-C v

un cong ca lin kt C-Htrong PLA.

1.2.2. Khi lng mol v cu trc phn t

Khi lng mol v phn b khi lng mol ca PLA c nh hng n tnh cht

gia cng, tnh cht c v tnh phn hy ca polyme. Khi lng mol ca polyme

thng c xc nh bi sc k thm gel (GPC) hay o nht dung dch polyme

[16]. Hai dung mi ph bin nht c s dng cho GPC l chloroform v

tetrahydrofurane (THF). Mt vi hng s Mark - Houwink (MH) c nu ra

trong mt s ti liu cho thy gi tr ca hng s ph thuc vo dung mi, nhit

dung dch, v c trng polyme [16]. Hng s chnh xc MH v Schulz - Blaschke

i vi PLA trong chloroform v THF c xc nh. i ci chloroform (30oC)

hng s c xc nh bi [] = 0,0131Mv0,777, [] = 0,0153Mw0,759, mL/g, v kSB =

0,302. i vi THF hng s c xc nh bi [] = 0,0174Mv0,736 mL/g, v kSB =

0,289. GC, GC-MS, hoc HPLC c th c s dng tch phn oligome khi

lng phn t thp ca axit lactic. Trong thng bo gn y, HPLC c kh nng xc

nh nh lng tng oligome ring r v phng php ny cng ph hp cho

polyme ha theo c ch pht trin tng bc ca axit lactic n KLPT khong 3000

g/mol [22]. Mt phng php khc c s dng phn tch cu trc PLA v

phn tch khi lng mol l 1H-NMR bi v nguyn t hydro trong n v PLA ca

nhm methyl ( = 5,15) v methyl cnh nhm hydroxyl cui mch ( = 4,4) c th

c nh lng t ph .

1.2.3. S chuyn trng thi nhit:

PLA l mt polyme nhit do c th to thnh hnh dng mong mun bng gia

cng nng chy trn nhit nng chy (Tm). Nhit nng chy v nhit

chuyn trng thi thy tinh (Tg) ca PLA ph thuc nhiu vo khi lng mol v

tinh khit quang hc ca polyme. Nhng ng dng chnh ca PLA l lm bao b v

vt liu sinh hc, Tm v Tg qui nh ph hp ca polyme i vi nhng ng dng


29

ny. Nhng hiu bit chnh xc v Tm v Tg v nhng yu t nh hng n chng

l thit yu khi pht trin nhng sn phm mi da trn PLA [16]. Chuyn trng

thi nhit (Tg, nhit kt tinh Tc, v Tm) v nhng entanpy lin quan ca PLA

thng c xc nh bng phng php nhit lng qut vi sai (DSC), thng

thng vi tc gia nhit 10oC/pht [16]. Tc gia nhit v lm lnh DSC nh

hng n entanpy nng chy v kt tinh, ngoi ra cn c s nh hng ca khi

lng mol ca polyme. Nhit nng chy cn bng (Tmo) ca PLA l 207oC,

nhng thp hn i vi PLA khi lng phn t cao (170-180oC) do bi s c mt

ca isome quang (enantiomer) v nhng tp cht gy ra s khng hon ho ca tinh

th [16]. kt tinh ca mt polyme da trn axit lactic c m t nh phn trm

ca kt tinh cc i l thuyt ca PLA khi lng mol ln. Entanpy nng chy

i vi 100% PLA kt tinh thng nhn c l 93,1 J/g. Phc lp th 100% PLA

kt tinh c gi tr entanpy cao hn nhiu (142 J/g) bi s khc bit trong cu trc

tinh th. Phng php nhiu x tia X (XRD) c dng kho st chiu di trong

tinh th polyme v nhng thay i v kt tinh ca vi si PLA [16]. Nhiu x tia

X gc nh (SAXS) hoc nhiu x tia X gc ln (WAXS) l nhng phng php

hu ch kho st hnh thi hc tinh th polyme v thng i km vi phng

php DSC trong nghin cu mng PLA, PLA phc lp th, hoc copolyme Poly(L-

lactide-co-meso-lactide) [16]. Knh hin vi quang hc phn cc cng thng c

s dng nghin cu bn cht s hnh thnh spherulit ca vt liu da trn PLA.

1.2.4. tinh khit quang hc v s raxemic ha

iu kin tin quyt nhn c isome quang homopolyme l s s dng

nguyn liu u tinh khit quang hc axit lactic. Raxemic ha ca bn lactoyl c th

xy ra trong bt k giai on no ca qu trnh polyme ha. S raxemic ha thng

ch xy ra nhit ln hn 200oC, nhng cng ph thuc vo xc tc v nhng

yu t khc [22]. tinh khit quang hc ca PLA c th c xc nh bng phn

cc k trong dung mi ph hp nh chloroform ti 589 nm []589 v phng php

ny c th cho thng tin v ng hc qu trnh polyme ha [22]. quay cc ca


30

isome quang c tinh khit cao PLLA v PDLA thng thng nm gia |140| v

|156|. Thng tin v cu hnh chui polyme cng c xc nh bng ph cng

hng t ht nhn (13C-NMR).

1.2.5. S phn hy ca PLA

Lng d xc tc, monome, v oligome lm gim nhit phn hy v tng tc

phn hy nhit ca PLA [16]. S thay i cu trc gy ra bi phn hy nhit c

th nh hng n nht, tnh cht lu bin, v tnh cht c l ca PLA v l kt

qu gy ra nhng vn lin quan n gia cng nh to khi. Nhng kha cnh

chung ca phn hy nhit ca PLA c xc lp t nhng nm 80 vi nhng

phng php nh phn tch nguyn t, IR, NMR, phn tch nhit trng lng

(TGA), DSC, v phn tch nhit thnh phn bay hi (TVA). bn nhit ca PLA

bao gm ht khi lng, lng cn khng bay hi, cng nh nhit phn hy

nhit v phn trm ht khi thng c xc nh bng TGA theo c hai kiu dc

ng nhit v gia nhit [16]. TGA cng c th c s dng nghin cu ng

hc phn hy nhit ca PLA. TVA-MS, nhit phn (py)-MS, py-GC/MS, hoc TGA

kt hp vi FT-IR (TGA-FT-IR) thng c s dng phn tch sn phm phn

hy nhit ca PLA. Loi v t l tng i ca cc sn phm phn hy nhit ca

PLA ng vi nhit phn hy v qu trnh phn hy xy ra trong h ng hoc

m. Cc sn phm phn hy nhit PLA c nhn bit bao gm lactide v nhng

oligome dng vng c kch c khc nhau, carbon dioxide, carbon monoxide, axit

acrylic, methane, ethylene, propylene, methylether (sn phm phn mnh),

acetaldehide, v butan-1,3-dion. S trao i ester back bitting, l qu trnh trans

ester ha ni phn t to thnh lactide v cc oligome vng c chng minh l

qu trnh phn hy nhit chnh ca PLA. Khi c mt ca xc tc Sn, hoc Mg, hay

Ca oxide, s to thnh c chn lc lactide c th t c khi la chn nhng iu

kin ph hp.

PLLA thng c iu ch bng phn ng trng hp m vng L-lactide, v

trong qu trnh L-lactide thu li t s phn hy nhit c quay vng. c tnh


31

trng hp - kh trng hp ny l mt trong cc tnh cht c th ca PLLA v qu

trnh kh trng hp trn thc t c dng iu ch L-lactide t cc oligome

trong qu trnh sn xut cng nghip [22]. V vy tnh cht ha hc c trng ny

khin PLLA c th c xem nh mt nguyn liu u vo trong ti ch cht do.

Tuy nhin, s phn hy nhit ca PLLA din ra phc tp hn so vi phn ng

to L-lactide n gin. V d, Duda v Penczek, hay Witzke v cc cng s tm

ra rng nhit trn v cc ch s nhit ng hc cho cn bng trong trng hp

lactide. Mc du vy, cc ch s tm c thay i trn mt din rng. Nng lng

hot ha (Ea), ca qu trnh phn hy cng c cho l thay i mt cch bt

thng t 70 ti 270 kJ mol-1 ty theo qu trnh phn hy nhit. Rt nhiu loi sn

phm cng c tm thy trong qu trnh nhit phn PLLA nh oligome vng v

cc ng phn diester [16]. Mt vn nghim trng khc ca qu trnh ti ch

PLLA l s ng phn ha to ra cc ng phn quang hc: meso- v D-lactide,

nhng cht ny gy ra nhng kh khn ln trong vic ti to PLLA thng qua vic

lm gim kh nng kt tinh v mt s tnh cht hu ch khc. Nhng v d sau cho

thy c rt nhiu c ch v yu t nh hng ti s kh trng hp PLLA [18].

Trong vic ti to nguyn liu, iu quan trng l phi kim sot c c ch phn

hy to ra L-lactide c chn lc. Khi t c quy trnh kim sot th PLLA

s nghim nhin c dng rng ri hn nh mt vt liu ph hp cho x hi bn

vng trong tng lai.

Gn y, vi mt lng nh kim loi cng c coi nh l xc tc cho qu trnh

trng hp, nh xc tc thic (Sn) ln qu trnh nhit phn PLLA. Mt s cht xc

tc khc c tc dng kim sot qu trnh kh trng hp PLLA c Nishida v

cng s tm ra, chng hn xc tc MgO v Al(OH)3 to ra L-lactide mt cch

chn lc t PLLA [16]. S ng phn ha tip tc l mt trong nhng vn

nghim trng ca qu trnh ti ch nguyn liu cho PLLA bi n c th xy ra

khng ch trong qu trnh kh trng hp m cn c trong lc tn ti trng thi

monome vng sau phn ng. Kopinke v cng s tng thng bo rng s ng


32

phn ha din ra thng qua s hn bin ha ester-bn axetal (ester-semiacetal

tautomerization) ca mch chnh PLLA (S hnh 1.17a). Fan v cng s

xut mt c ch ng phn ha khc: phn ng SN2 ti mt tm carbon bt i c

th xy ra nh mt phn ng t ngt mch t u mch hot ng: R-COOCa+ ca

phn t PLLA (S hnh 1.17b)

(a)

n v L-lactate n v D-lactate

(b)

Meso-lactide

Hnh 1. 17: Cc c ch ng phn ha: (a) s hn bin ha ester- bn axetal,

(b) phn ng SN2 ti mt trung tm bt i

1.3. Cc vt liu tng hp ca PLA 1.3.1. Nghin cu tng hp PLA/ PEG

PLA c rt nhiu u im so vi cc polyme khc, ni bt trong s l kh

nng ti sinh, tnh tng hp sinh hc, kh nng gia cng tt v tiu tn t nng

lng trong qu trnh sn xut [15]. PLA c coi l vt liu sinh thi tim nng

cho tng lai, tuy nhin n c mt s nhc im lm gim kh nng ng dng

trong thc t nh:


33

- do km: PLA l mt vt liu gin vi dn di khi t nh hn 10%.

Mc d c bn ko v ng sut n hi tng ng vi polyethylenterephtalat

(PET) nhng c gin cao khin PLA t c p dng trong cc ng dng cn c

bin dng do cao nh vt hay np c nh xng [15].

- Tc phn hy chm: PLA phn hy thng qua s thy phn mch chnh vi

cc lin kt ester. Tc phn hy ph thuc vo cc yu t nh: tinh th ca

PLA, khi lng phn t, a phn tn ca phn t khi, hnh thi hc, tc

khuch tn ca nc trong polyme, ng u lp th ca mch polyme [15]. Tc

phn hy l mt trong nhng tiu chun quan trng cho cc ng dng trong y

sinh.Tc phn hy chm dn ti thi gian tn ti lu ca cc thit b lm t PLA

trong c th (c th ln ti hng nm trong mt s trng hp [11]).Tc phn

hy chm cng l mt trong cc vn ng lu tm trong ng dng cho sn xut

cc hng ha thng dng.

- Tnh k nc: PLA tng i k nc vi gc thm t vi nc l gn 80oC.

Tnh cht ny ng ngha vi tnh tng hp vi t bo km, cng nh c kh nng

gy vim nhim vt ch khi tip xc trc tip vi cc dch trong c th [11].

- Thiu cc nhm hot ng ph: PLA kh tr v mt ha hc v n khng c cc

nhm hot ng ph. iu ny khin cho vic bin tnh PLA kh khn hn.

m rng hn na kh nng ng dng ca PLA, vic bin tnh vt liu ny,

c bit l cc tnh cht c l v kh nng gia cng ca n l v cng cn thit.

Phn sau s cp ti cc tnh cht c l chnh ca PLA v cc phng php

thng c p dng bin tnh cng nh tng kh nng gia cng ca PLA.

V tnh cht c l th PLA l mt polyme nhit do ging nh thy tinh v c

cng cao. PLA c cc tnh cht gn tng ng vi polystyrene. PLA tng hp t

cc monome Llactide hoc Dlactide l cc polyme bn tinh th, trong khi polyme

thu c t cc monome hn hp nh meso-lactide hay hn hp racemic ca D- v

L- lactide c dng v nh hnh [11]. PDLLA di dng v nh hnh ch yu c


34

dng trong cc ng dng y sinh nh lm cc thit b phu thut t tiu hay cht bc

thuc nh chm. Cn PLLA, dng ph bin nht trong cc PLA c tng hp,

c dng trong cc ng dng i hi tnh bn c l cao hn.

- Tnh cht ko v un: PLA thng c bit n nh l mt polyme c cc tnh

cht c l tt vi bn ko nm trong khong 50-70 MPa, ng sut n hi

khong 3000-4000 MPa, dn di khi t trong khong 2-10%, bn un ~100

MPa, v ng sut un khong 4000-5000 MPa [8]. PLA c tc kt tinh chm, do

a phn cc mu PLA thu c thng qua qu trnh c p lc thng thng u

l v nh hnh [10]. Thng thng, bn ko ca PLA v nh hnh nm trong

khong 40-53 MPa. Sau qu trnh mu 105oC, PLA c tinh th t 45% ti

70%, dn ti bn ko tng ln n khong 47-70 MPa trong cng mt khong

phn t khi. nh hng ca phn t khi ln cc tnh cht ko v un c th

hin r hn trn cc mu sau vi bn ko tng t 47 ln 66 MPa khi khi lng

phn t tng t 20000 ln 70000 g/mol (phn t khi theo nht, M). PLA v

nh hnh vi phn t khi ln hn 30000 g/mol c cc tnh cht c l tng chm

hn, trong khi vi PLA sau , iu ch xy ra sau khi khi lng phn t ln hn

50000 g/mol.

S ph thuc ca tnh cht c l ca PLA vo phn t khi c nghin cu

bi nhiu tc gi trc y. Engelberg v Kohn tm ra rng khi phn t khi tng t

107000 ln 550000 g/mol, bn ko tng 20% [11].Thng thng vng phn t

khi ln, s bin thin tnh cht c l din ra chm hn. Mt s tc gi cng a ra

cc gi tr tnh cht ko hi khc so vi cc mu PLA thng mi [10]. Cc tm

PLA v nh hnh ca NatureWorks (k hiu 4060, ~ 10% ng phn D-) c cc gi

tr bn ko, ng sut n hi ko v dn di khi t ln lt l 44 MPa, 2500

MPa, v 7%. PLA bn tinh th t NatureWorks (k hiu 4032, ~ 1,5% ng phn

D-) c cc gi tr trn ln lt l 54 MPa, 2600 MPa, v 9%. S khc bit nh trong

cc gi tr c thng bo c th l do PLA thng mi thng c sn xut bng

cch ng polyme ha Llactide vi mt lng nh mesolactide lm gim


35

tinh th v gin ca vt liu. Mt nghin cu khc li bo co PLA ca hng

Mitsui Fine Chemicals (k hiu Lacea H.100E) c cc gi tr bn ko, ng sut

n hi ko v dn di khi t ln lt l 66 MPa, 3300 MPa, v 1,8% [11].

Trong khi PLA ca hng Purac c gi tr ng sut n hi thp hn ti 1151 MPa v

dn di khi t l 14,5% [10]. S khc bit v cc tnh cht c l cng c th bt

ngun t cc phng php khc nhau c dng chun b mu o. Tuy nhin,

cc s liu cng b u cho thy PLA c ng sut n hi, bn ko cao v

kh nng bin dng thp.

- bn va p: bn va p ca PLA b nh hng rt ln bi vic ct. Cc

gi tr bn va p Izod ca PLA c tinh th thp (3-9%) nm trong khong 2-

3 kJ/m2. Vi PLA c tinh th cao (45-70%), gi tr ny vo khong 3-7 kJ/m2

[10]. Vi trng hp bn va p khng ct, s khc bit gia cc mu c tinh

th khc nhau cn ln hn. Mt nghin cu khc cho cc gi tr bn va p ct

nm trong khong 2,02,6 kJ/m2 [10] v bn va p khng ct l 12 kJ/m2 [10].

S ph thuc ca bn va p ct vo bn knh vt ct c nghin cu bi

Grijpma v cc cng s cho thy gi tr ny gim t 2,2 xung 1,2 kJ/m2 khi bn

knh vt ct gim t 1,0 xung 0,1 mm [11].

Mt iu ng lu l qu trnh gia cng c nh hng ng k ti bn va

p ca PLA. PLA vi phn t khi rt ln (~ 780000 g/mol) cho cc gi tr bn

va p gim mnh t 47 kJ/m2 ca polyme va c tng hp xong xung cn 12

kJ/m2 cho mu sau khi c [11]. iu ny c gii thch bi s gim tinh th

do vic lm lnh nhanh trong qu trnh c p. Phn t khi cng c nhng nh

hng ti bn va p, nht l vi PDLLA

T nhng kt qu trn, ta c th thy PLA l mt vt liu c bn va p tng

i km. Ty vo tng ng dng c th m ta c th thay i bn va p da

trn tinh th v khi lng phn t.


36

- cng: cng Rockwell ca PLA thng thay i t 70 90 theo thang H

hay ~120 theo thang L [10]. cng Rockwell rt t ph thuc vo tinh th nh

c th thy khi gi tr ny ch thay i t 83 ti 88H vi PLA v nh hnh v t 82

ti 88H vi PLA bn tinh th. Gi tr ny cng t ph thuc vo phn t khi. [10].

Trong s cc polyme c kh nng phn hy sinh hc, PLA c ng sut n hi v

cng cao. Nhng c tnh ny c lin h cht ch vi thnh phn ha hc ca

polyme. S tn ti ca cc nhm chc ester trong mch cng nh cc mch ln

cn trn thc t nh hng ti cc tng tc ha l gia cc mch polyme lm

gim kh nng trt ca phn t trong qu trnh bin dng khi c lc tc dng. Cc

tng tc phn cc gia cc mch polyme vi nhau dn n nhit thy tinh cao,

v do l cng cao ca PLA.

PLA l mt polyme c cc tnh cht c l tt vi ng sut n hi khong 3000-

4000 MPa v bn ko ~ 50 MPa. Do , trn l thuyt PLA hon ton c th

thay th cho cc polyme truyn thng trong rt nhiu cc lnh vc nh bao gi, si,

thng cha Tuy nhin kh nng bin dng km ca vt liu ny hn ch nhiu

ng dng ca n. PLA c nhit chuyn thy tinh khong 60-70oC, v vy n rt

gin nhit thng, dn n d b ph hy do rn nt. C nhiu phng php

c p dng ci thin tnh cht ca PLA nh ng trng hp, to t hp vi cc

polyme c kh nng phn hy sinh hc khc, lm do ha, to (nano) composite

Trong , t hp hai hay nhiu polyme l mt cch d dng nht v cng thng l

cch r nht tng hp ra cc vt liu polyme s hu cc tnh cht mong mun.

PEG l polyme ca ethylene oxide thng tn ti c ba dng lng, sp v bt

rn ty thuc vo khi lng phn t. PEG l mt polyme nhit do, c kt tinh

cao v c kh nng tan trong nc. PEG vi phn t khi thp thng c dng

lm cht do ha cho PLA Younes v Daniel nghin cu tnh tng hp ca hai

polyme ny trong t hp iu ch bng phng php dung dch. H quan st thy

rng khi t l ca mt thnh phn ln hn 20% khi lng, thnh phn c th kt

tinh v t hp s bao gm cc tinh th bn tng hp phn b trong mt nn v


37

nh hnh. Trong t hp vi mt thnh phn nh hn 20% th ch c thnh phn

chnh c kh nng kt tinh. Sheth v cc cng s ch to t hp PLA-PEG vi

cc nng khc nhau. Tnh tng hp v tnh cht c l ph thuc nhiu vo nng

PEG [9].

Trong lun vn ny, t hp PLA-PEG vi cc t l PEG khc nhau c iu

ch theo phng php trn nng chy nhm thay i cc tnh cht ca PLA cho ph

hp vi cc ng dng khc nhau. Mc tiu chnh ca cng vic ny l tm ra nh

hng ca hm lng PEG ln cc tnh cht c l ca t hp PLA-PEG nh bn

ko, ng sut n hi v dn di khi t.

1.3.2. Tng hp copolyme ca axit lactic v poly (ethylene glycol).

PEG c kh nng ha tan trong nc, dung mi hu c phn cc v khng tan

trong cc dung mi khng phn cc nh ethyl eter, heptan. PEG c t c tnh, d

gii phng nhanh chng ra khi c th [16] khin n tr thnh mt comonome thch

hp cho vic iu ch copolyme PLA-PEG. S ng trng hp ca axit L-lactic

(LLA) k nc vi PEO (poly ethylene oxide), poly propylene oxide a nc c

s dng trong phn ng tng hp diblock hoc triblock copolyme [16]. Cc

copolyme ny c tnh phn cc hn, do hn v tnh phn hy sinh hc cao hn

PLLA homopolyme [16]. Kh nng phn hy sinh hc v tnh tng hp sinh hc

ca cc copolyme ny mang li tim nng ng dng ln trong vic ch to cc ht

nano cu trc li v vi min PEO a nc hnh thnh ln phn b mt cn min

PLA k nc hnh thnh phn li trong [16].

Cc diblock v triblock polyme c tng hp t phn ng trng hp pha lng

hoc rn s dng Sn(Cl2) [13] hoc [Sn(Oct) 2] nhit cao (100-150) trong nhiu gi, kali tert-butoxit (potassium tert-butoxide), natri hydrit (sodium

hydroxide), canxiumhydride / Zn , hoc km kim loi [9]. Nhit trng hp cao

thng lm gim khi lng phn t ca khi PLLA [9]. Mt lng ln cc sn

phm c iu ch bng cch thay i khi lng phn t ca PEG (1000-


38

30,000 g/mol), hoc thnh phn ca monome LLA trong ngun nguyn liu ban

u. Cu trc ca triblock copolyme c m t trong hnh 1.18.

Hnh 1. 18: M t cu trc ca triblock copolyme P(LLA-b-PEG-b-LLA)

1.3.2.1. S trng hp m vng ca PEG v lactide

Nhng polyme ny c th c tng hp bng cch trng hp m vng gia

PEG hoc nhm dn xut ca n nh metoxyl polyethylene glycol (m PEG) v

lactide (hnh 1.19) [15], vi xc tc l mui thic. c bit l cc hp cht cha

thic c kh nng xc tc cao. Tuy nhin, do c tnh cao ca cc kim loi nng nn

gi s Kricheldorf v cng s s dng xc tc axit axetic bismuth [15]. Chng ta

c th kim sot di ngn ca copolyme PEG v L-lactide bng cch thay i t

l monome v cht khi mo, cc copolyme vi cu trc phn t khc nhau c th

c tng hp nh: dng A-B, copolyme stelate, A-B-A triblock copolyme,

multiblock copolyme, v reticular copolyme

Hnh 1. 19: S tng hp mPEG-PLA


39

1.3.2.2. Trng hp m vng anionic.

Trong trng hp m vng anionic, cc cht xc tc thng dng gm c

potassium alkoxit, sodium alkoxit, litibutyl [8]. Otsuka v cng s tng hp

c 3,3-potassium-dietoxyl propanol ([C2H5O]2CHCH2OK) t cht phn ng ban

u l 3,3-dietoxyl-propanol ([C2H5O]2CHCH2OH) v potassium naphthalene (K-

Naph), n c th ha tan trong tetrahydrofuran (THF), v sau tng hp c

khi copolyme -acetal-PEG-PLA nh trng hp m vng anionic cng vi

ethylene oxide, trong axit lactic (LA) l cht phn ng v 3,3-potassium-dietoxyl

propanol l cht khi mo (Hnh 1.20).

Hnh 1. 20: S tng hp poly (ethylene glycol) poly( axit lactic) copolyme

ui acetal

1.3.3. Nano clay

Khong st Bentonit c thnh phn chnh l Montmorillonit (MMT) vi cng

thc ha hc tng qut: Al2Si4O10(OH)2. Cu trc tinh th ca MMT c to thnh

bi hai mng li t din lin kt vi mng li bt din gia to nn cu trc lp

nh trong hnh 1.21 [6]. Mi lp cu trc c pht trin lin tc trong khng gian

theo hng a v b. Trong khng gian gia cc lp cn tn ti nc nh lp v

hydrate ca cc cation trong . Cc lp c xp chng song song vi nhau v


40

ngt qung theo trc c, cu trc ny to nn mng khng gian 3 chiu ca tinh th

MMT. Chiu dy mi lp cu trc ca MMT l 9,2 - 9,8Ao. Khong cch gia cc

lp trng thi trng n khong t 5 - 12Ao ty theo cu trc tinh th v

trng n.

Cation trao i

Hnh 1. 21: Cu trc mng tinh th 2:1 ca MMT

Cc lp cu trc ca MMT thng tch in m, trung ha lp in tch ny,

st MMT tip nhn cc cation t ngoi vo. Ch mt phn nh cc cation ny (Na+,

K+, Li+) nh v mt ngoi ca mng cn phn ln nm vng khng gian gia

cc lp. Trong st MMT cc cation ny c th b thay th bi cc cation ngoi dung

dch vi dung lng trao i ion ty thuc vo mc thay th ng hnh trong


41

mng. y chnh l nguyn l cho vic iu ch nano clay hu c. Khi cc cation

ny c thay th bng cc cation amoni kch thc ln, khong cch khng gian

c s gia hai lp MMT s tng ln t 9,6 Ao ln n vi chc Ao ty thuc vo

kch thc ca cation th. Nguyn l iu ch nano clay hu c c th hin trong

Hnh 1.22 [19].

Hnh 1. 22: Nguyn l iu ch nano clay hu c bng cc cation amoni khc

nhau

Trong ch to vt liu nanocomposite, t c nhng ci tin v tnh cht

nh mong mun th s phn tn ca nanoclay trong vt liu nn polyme c tnh cht

quyt nh. Ty thuc vo tng hp gia mt nano clay a nc v polyme nn

(thng l k nc) m vt liu t hp ch to c c th c mt trong hai dng

sau:


42

- Clay khng phn b u dng nano vo nn polyme (microcomposite).

Trng hp ny xy ra khi tng hp gia clay v polyme thp nn cc mch

polyme khng th xen vo gia cc lp clay. Khi tnh cht ca vt liu thu c

hu nh khng tng hoc thm ch cn gim so vi trc khi thm clay.

- C s xen k mt phn polyme vo gia cc lp clay. Tnh cht ca vt liu

c ci thin nhng khng nhiu. Tng lp aluminum silicate c phn b u

trong polyme nn. Khi cc tnh cht c, l, nhit ca polyme c tng cng

nhiu nht. Tuy nhin rt kh t c trng thi ny m thng ch l s kt

hp gia cc nanocomposite xen k mt phn v phn tn hon ton [6].

1.3.4. Nano bc

Nano bc l vt liu c din tch b mt ring rt ln, c nhng c tnh c o

nh:

- C tnh khng khun, chng nm, dit to, kh mi hi tanh.

- C kh nng tiu dit hn 650 chng vi sinh vt gy bnh v khng b cc

chng vi sinh vt thch nghi nh nhiu cht st trng khc.

- C tc dng khng khun nh mt cht xc tc nn t b tiu hao trong qu trnh

s dng.

- Ch tiu dit cc vi khun c hi (gram m), khng gy hi cho c th con

ngi v ng vt vi liu lng tng i cao.

- bn ho hc cao, khng b bin i di tc dng ca nh sng v cc tc

nhn oxi ho kh thng thng [1].

Nano bc kim loi thng c iu ch t mui bc kim loi bng phn ng

kh. Tc nhn kh l cc aldehyde nh aldehyde focmic (HCHO) v ng glucozo

(C6H12O6).


43

RCHO + 2Ag+ + 3NH3 + H2O 2Ag + RCOONH4 + 2NH4+

RCHO + 2AgNO3 + 3NH3 + H2O 2Ag + RCOONH4 + 2NH4NO3

Cu to mixen ca ht bc khi

khng c cht hot ng b mt

Cu to ca ht keo nano bc khi c

s bo v ca cht hot ng b mt

Hnh 1. 23: Cu to mixen ca ht bc khi c v khng c s bo v ca cc

cht hot ng b mt.

Nano bc c ch to di dng cc h keo nano bng phng php s dng

cht hot ng b mt. Trong qu trnh kh ion Ag+ thnh Ag, b mt ht keo nano

bc hp ph ion Ag+ trong dung dch v to ra lp ion to th dng trn b mt.[1]

Cht hot ng b mt di dng RCOO- (R l gc hydrocarbon) b hp ph ln b

mt lp ion to th. Nh vy, cc ht keo tr nn bn vng v khng b keo t li

vi nhau. S c mt ca cc cht hot ng b mt cng gip cho cc ht keo va

c tnh a nc va c tnh a du. Do , cc ht keo nano bc c th phn tn tt

v bn vng trong c mi trng phn cc v mi trng khng phn cc. [1].


44

Chng 2: THC NGHIM

2.1. Ha cht v thit b 2.1.1. Tng hp poly-axit lactic

- Axit L-lactic c tng hp t ln men rm r do Vin Cng Ngh Sinh Hc

thc hin.

- Xc tc: antimony tri oxide (Sb2O3), km sterat (zinc sterate Zn(C18H35O2)2);

thic dibutyl dimethoxyl; 1,4-butandiol triphenylphotphin.

- Thic (II) 2-ethylhexanoate (95%) v c ct li p sut gim (0,1 mmHg)

trc khi s dng. L-lactide c kt tinh li trong lng va toluen

- Nc ct v cc dung mi cn thit.

2.1.2. Thit b tng hp v tinh ch lactide.

(a)


45

(b)

Hnh 2. 1 Thit b tng hp lactide (a) v tinh ch lactide (b)

2.1.3. Ch to cc vt liu t hp t poly-axit lactic

- PLA dng bt c iu ch t cc nghin cu trn

- Bentonit c tinh ch t khong st Bnh Thun.

- Cc ha cht v dung mi c t mua t Sigma-Aldrich v Merck.

2.2. Quy trnh th nghim 2.2.1. Tinh ch axit lactic

Axit lactic sau qu trnh ln men c tin hnh loi nc bng mng ultrafilter

(mng siu lc) c c axit lactic ng thi kt hp loi tp cht. Quy trnh c

c axit lactic t dch ln men s dng cng ngh mng c m t trong hnh 2.1.

C c axit lactic bng h thng thm thu ngc (RO) s dng mng: Filtec

TW30-1812-100 (DOW-USA). Loi b >90% cc loi mui. Nhit hot ng ti

a 45oC. p sut hot ng l 30 bar c pH nm trong khong t 2-11.


46

Tinh sch axit lactic bng ct trao i ion: vi ct cation l ct Cation-Resin

(Lewaltit S2568), ct anion l ct Anion-Resin (Lewaltit S3428). Mc tinh sch

ca axit lactic sau bc trao i t > 99%

Lc th bng mng ultrafilter: mng ultrafilter 300 (ricon, USA). C Kch thc

mng: 0,01 M. Nhit ti a hot ng: 40oC. p sut: 3 bar. Tc lc: 300

l/h. Loi b c 100% vi sinh vt.

Hnh 2. 2: Quy trnh v tng s cho vic tch axit lactic bng cng ngh mng

Sau khi thu c axit lactic c nng >50% tin hnh chuyn sang quy trnh

ester ha v thy phn, quy trnh c m t trong hnh 2.3

T axit lactic c nng >50%, tip tc c c chn khng p sut thp n

khi dung dch axit lactic t ~80%. Ly 450 ml dung dch axit ny cho vo bnh cu

1000 ml. Sau cho thm 400 ml butanol v 1 ml H2SO4 c nng (a pH v 1)

vo bnh cu, chng ct hi lu ng thi tin hnh loi nc. Lng butanol thm

vo t trn xung xc tin cho qu trnh phn ng xy ra nhanh chng. Tin

hnh phn ng trong 2h. ngui dung dch phn ng sau trung ha bng soda

a pH v 5. Lc ra dung dch v tip tc chng ct tinh ch butylactate.

Qua 3 ln chng ct phn on chng ta thu c butylactate tinh khit khng mu.

Axit lactic tinh khit thu c bng cch thu phn hn hp butyl lactate vi HCl


47

v nc. Hn hp ny c un nh v ct. Hn hp sau thy phn c tch v

phn lp thu axit lactic. Tip tc c chn khng axit lactic bng cch ht chn

khng thu c axit lactic tinh khit.

Hnh 2. 3: S quy trnh tch axit lactic bng phng php ester ha.

2.2.2. Tng hp PLA 2.2.2.1. Tng hp oligome PLA

Tng hp oligome PLA gm hai giai on

Giai on 1: Giai on loi nc lm khan axit lactic:

Axit lactic c cho vo bnh cu 250 ml ni vi b chng ct. Gia nhit bnh

phn ng v ct loi nc. Qu trnh loi nc c tin hnh trong khong thi

gian t 0-3h, nhit 100-140oC, p sut 10mmHg

Giai on 2: tng hp oligome PLA


48

Axit lactic lm khan trn c s dng tng hp oligome. Tip tc gia

nhit phn ng trong iu kin p sut thp. Phn ng xy ra khng cn xc tc.

Nc loi ra trong bnh phn ng cn c loi b. p sut gim t t khng

xy ra hin tng si qu mnh lm cht lng pht sang bnh cha. Sn phm thu

c l cht lng c nht cao v c s dng cho phn ng tip theo m khng

cn tinh ch thm.

a) Kho st iu kin nh hng ti qu trnh tch loi nc lm khan axit lactic

Axit L-lactic thu c t qu trnh ln men cn c tch loi nc lm khan

axit lactic. Axit L-Lactic ln men c cho vo bnh cu 250 ml ni vi b chng

ct. Gia nhit bnh phn ng. Nc loi ra trong qu trnh phn ng c ct b.

Qu trnh loi nc c tin hnh trong khong thi gian t 0-4h, nhit 100-

1400C, p sut 10mmHg. Kt qu qu trnh loi nc c trnh by trong bng 3.1.

b) Kho st iu kin nh hng ca nhit ln phn ng tng hp oligome poly-axit lactic.

Axit lactic lm khan trn c s dng tng hp oligome. Chng ti tin

hnh kho st nh hng ca nhit ln phn ng tng hp oligome poly-axit

lactic trong khong nhit t 180-240 oC. Thi gian phn ng l 4h, p sut

10mmHg. Khong nhit thch hp nht thu c hiu sut cao l khong 200 oC. Kt qu c a ra trong hnh 3.2.

c) Kho st iu kin nh hng ca thi gian phn ng ln KLPT trung bnh ca oligome PLA.

Axit lactic lm khan trn c s dng tng hp oligome. Da vo nhng

kt qu t c chng ti tin hnh phn ng nhit l 200 oC, p sut

10mmHg, thc hin kho st thi gian phn ng trong khong thi gian t 4-7h.

Kt qu c th hin trong phn 3.3.

2.2.2.2. Tng hp L-lactide.


49

Oligome PLA c cho vo bnh cu 250 ml c khuy t, sau cho mt lng

xc tc c tnh trc (1.5% khi lng oligome) c thm vo bnh phn

ng. Xc tc c s dng l ZnO v Sb2O3. Bnh phn ng c ni vi ct ct v

c gia nhit, phn ng xy ra trong iu kin p sut gim. Lactide th to ra

c chng ct v thu vo bnh cha lactide t trong bt cha du 90oC ngn

chn s ng rn ca lactide. Dung dch lactide thu c c mu vng nh.

a) Kho st nh hng ca cht xc tc v hm lng Phn ng kh trng hp oligome tng hp lactide mch vng l phn ng

back-bitting ca cc nhm OH cui mch. Phn ng ch xy ra di s c mt ca

cc loi xc tc kh trng hp nh: bt thic, cc hp cht ca thic, ZnO , cc hp

cht ca kim loi qu, cc hp cht ca antimon (Sb2O3)... Hai loi xc tc c la

chn trong nghin cu ny l ZnO v Sb2O3; ln lt cc nng ca hai loi xc

tc ny c kho st ZnO (0,05; 0,1; 0,15). Sb2O3 (0,05; 0,1; 0,15; 0,2). Kt qu

c a ra trong bng 3.3 v hnh 3.4.

b) Kho st nh hng ca KLPT trung bnh ca oligome PLA n hiu sut tng hp lactide

Chng ti tin hnh kho st KLPT trung bnh t khong 500 n 1100 g/mol.

Tt c cc mu th nghim u c thc hin di cng mt iu kin nh nhau.

Ly cng 50 g oligome PLA. Thi gian phn ng l 4h, cht xc tc l Sb2O3

(0,15% khi lng cht phn ng). Ch khc nhau v KLPT . Kt qu c chng

ti a ra trong hnh 3.5.

c) Kho st nh hng ca nhit phn ng Phn ng kh trng hp lactide oligome tng hp lactide l phn ng thu

nhit. nghin cu nh hng ca nhit ti hiu sut chuyn ha lactide

oligome thnh lactit, chng ti tin hnh thc hin phn ng kh trng hp

oligome trong mt khong nhit rng t 180oC n 240oC.

Tt c cc mu th nghim u c la chn vi cc thng s c bn l nh

nhau, lng lactide oligome KLPT trung bnh trong khong 825 g/mol a vo


50

phn ng l 50g, p sut 100mmHg v thi gian phn ng l 4 gi, hm lng xc

tc Sn2O3 l 0.15% (khi lng). Kt qu nghin cu nh hng ca nhit ti

hiu sut tng hp lactide c th hin trn trong hnh 3.6 v nh hng ca nhit

ln t l to L-lactide c th hin trong hnh 3.7.

d) nh hng ca thi gian kho st nh hng ca thi gian phn ng n hiu sut to thnh lactide,

cc nghin cu c tin hnh trong khong thi gian khc nhau. Tt c cc iu

kin phn ng khc c la chn tng t nh nhau cho tt c cc mu th nghim

l: lactide oligome c KLPT trung bnh 825 g/mol, khi lng mu 50g, hm lng

cht xc tc Sb2O3 s dng l 0,15% so vi tng lng cht, nhit phn ng la

chn l 220oC, p sut 10mmHg. Kt qu kho st nh hng ca thi gian n

hiu sut to thnh lactit mch vng c trnh by trong hnh 3.8.

e) nh hng ca p sut p sut l mt trong nhng thng s quan trng nh hng ti tin trnh v

hiu sut ca phn ng. Qua kho st s b cho thy: iu kin p sut thng

khng to thnh lactide mch vng t phn ng kh trng hp lactide oligome. S

to thnh lactide ch xy ra khi thc hin phn ng di iu kin p sut thp.

nghin cu nh hng ca p sut n hiu sut tng hp lactide, cc th nghim

cng c thc hin vi cc iu kin c nh nh: khi lng oligome 50g, hm

lng cht xc tc Sb2O3 l 0,15% (khi lng), nhit phn ng 200-220 oC, thi

gian l 4h. y, ch thay i p sut ca khi phn ng. Kt qu kho st nh

hng ca p sut ti hiu sut ca phn ng tng hp lactide c th hin trong

hnh 3.9.

2.2.2.3. Tinh ch lactide th

Lactide th c trn v khuy vi mt lng nc tng ng 25oC trong 30

pht. Cho acetone vo dung dch v lm lnh xung -15oC. Hn hp sau c


51

khuy tip trong 30 pht. Sau quay li tm v thu hi cht rn, sy chn khng

40oC trong 48 gi.

Chng ti cng kho st cc iu kin nh hng n qu trnh tinh ch

lactide th nh nh hng ca nhit , thi gian, dung mi.

a) Kho st nh hng ca nhit v thi gian

Cng nhng iu kin ging nhau v vi nhng nhit c em kho st nm

trong khong t 15-35oC. Thi gian

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