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PRCTICAS DE TECNOLOXA DE POLMEROS(Curso 2011-12)
COMPORTAMENTO TRMICOETSEM
O obxectivo desta prctica afondar en diversos aspectos
relacionados co comportamento
trmico dos materiais polimricos: cristalinidade, memoria de
forma e transicin vtrea.
Realizaranse diversas experiencias para ilustrar os conceptos
de: temperatura de transicin
vtrea (Tg) e temperatura de fusin cristalina (Tm); memoria de
forma e tratamentos trmicos
nos plsticos (recocido). Tamn se iniciar aos alumnos no ensaio
de Calorimetra Diferencial de
Varrido (DSC).
1) Temperatura de transicin vtrea (Tg) e temperatura de fusin
cristalina (Tm)
Introdcense na estufa dous envases: un de poliestireno (PS) e
outro de polipropileno (PP) a
T=120C. Discutir que pasa.
2) Tratamento trmico de recocido (recristalizacin)
Introducimos unha rosca de polietilentereftalato (PET) na
estufa. Observar que pasa e
discutir por que.
PP PS PET
Tg = -20 C Tg = 74-109 C Tg = 73-80 C
Tm = 160-175 C Tm = 240-250 C Tm = 245-265 C
3) Efecto da historia trmica. Clculo da cristalinidade
Realizaranse diversos anlises DSC de mostras de PET con
distintas histoiras trmicas.
Comentar as diferenzas.
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Content determination
The content C of the component undergoing a transition or
chemical reaction in the evaluatedtemperature range is calculated
as follows:
CH
H100%
100%
=
C: Content [%]
H: Measured heat of transition/reaction [J/g]
H100%: Heat of transition/reaction of the pure component
[J/g]
(content = 100%)
Crystallinity determination
The crystallinity, C, of a semicrystalline material melting in
the evaluated temperature range iscalculated as follows
CH
H100%
100%
=
C: Crystallinity of a semicrystalline material
H: Measured heat of fusion [J/g]
H100%: Heat of fusion of the 100% crystalline material [J/g]
Literature values for some selected polymers:
Polymer Theoretical heat of fusion[J/g] (100% crystalline) *
Approx imate melt ingpeak temperature [C]
Polyethylene (PE) low density 293.6 110
Polyethylene (PE) high density 293.6 135
Polypropylene (PP) 207.1 165
Polyoximethylene (POM) 326.3 180
Nylon 6 (PA-6) 230.1 225
Polyethylene-terephthalate (PET) 140.1 255
Nylon 6,6 (PA-6,6) 255.8 260
Source: Advanced Thermal Analysis Laboratory, Oak Ridge National
Laboratory (ORNL) AndTh U i i Of T K ill (UT)
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! &PET BOTELLA
PET BOTELLA, 14. 3500 mg
! &PET BOTELLA 2 barr i do t r as enf . 1C/ sPET BOTELLA 2
barr i do t r as enf . 1C/ s, 14. 3500 mg
! &PET BOTELLA. Recoci do recr i st al i za
PET BOTELLA. Recoci do r ecri st al i za, 14. 3500 mg
Wg -1
1
C30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190
200 210 220 230 240 250 260 270 280 290
^exo PET docencia 16.03.2006 20:03:34
STAReSW 9.20ab: METTLER
