PLASTICS

AKHIL KRISHNAN G

DEFINITION AND CONCEPT

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids that are moldable

Macro molecularConsists large chain like molecules

containing carbon

PROPERTIES OF PLASTICS

Less brittle than glass ,hence can be made transparent and smooth.

Corrosion resistanceLow electrical and thermal conductivity, insulator Easily formed into complex shapes, can be formed,

casted and joined.Wide choice of appearance, colors and

transparenciesLight weight but posses good strength and rigidity.Low moisture absorbtion.Heat resistance.

TYPES OF PLASTICS

THERMOPLASTICS Thermoplastics are the plastics that do not

undergo chemical change in their composition when heated and can be molded again and again

THERMOSETTING PLASTICSThermosets can melt and take shape once;

after they have solidified, they stay solid. In the thermosetting process, a chemical reaction occurs that is irreversible

MANUFACTURE OF PLASTICS

The production of plastics can be roughly divided into four categories:

1. Acquiring the raw material or monomer.2. Synthesizing the basic polymer.3. Compounding the polymer into a material that can be used for fabrication.4. Molding or shaping the plastic into its final form.

1.Raw Materials

Historically, resins derived from vegetable matter were used to produce most plastics.

This included such materials as cellulose (from cotton), furfural (from oat hulls), oils (from seeds) and various starch derivatives.

 Today, most plastics are produced from petrochemicals which are widely available and tend to be cheaper than other raw materials.

2. Synthesis of the Polymer

The first step in plastic manufacturing is polymerization.

The two basic methods by which polymerization can occur are addition and condensation reactions.

 This is achieved by adding reinforcements such as glass or carbon fibers to the plastics, increasing their strength and stability.

Additives

Chemical additives can be used in the production of plastics to achieve certain characteristics. These additives include:

1. antioxidants to protect the polymer from degradation by ozone or oxygen

2. ultraviolet stabilizers to protect against weathering

3. plasticizers to increase the polymer’s flexibility

4. lubricants to reduce friction problems5. pigments to give the plastic colour

3.Shaping and Finishing

1.COMPRESSION MOLDINGPre-measured amount of polymer

introduced into the heated mold then the top half comes down and applies pressure. Usually uses thermosetting plastics and produces products like dishes, container caps, etc.

EXTRUSIONA device, called an extruder, forces softened

plastic through a shaped die from which it may emerge in almost any form, including a circular rod or tube, and a wide, flat sheet.

The driving force is supplied by a screw which provides constant pressure.

INJECTION MOLDING  Involves one or more extruders which force

melted plastic into a cold mold where it is allowed to set to the required shape.

  An adaptation of this method is injection blow molding which is used to make plastic pop bottles.

A thick-walled plastic tube is initially injection-molded around a blowing stick and is then transferred to a blowing mold.

The tube is reheated and expanded to the shape of the mold by passing air down the blowing stick.

THERMOSETTING RESINS

Once hardened and set, they do not soften with application of heat.

Reason: consist of linear, relatively low molecular wt

thermoplastic polymer chains with crosslinks which bond the chains together. when heated the entire structure becomes a single molecule.Objects made of this can be used at higher

temperatures without damage.More stronger and harder than thermoplastic

resins.

APPLICATIONS

Telephonic receivers, electric plugs, radio and TV cabinets, camera bodies, automotive parts, electric baker, switch panels.

EXAMPLESPhenol formaldehyde resinsUrea formaldehyde resinsMelanine formaldehyde resinsPolyester resins.Epoxy resinsSilicone resins

THERMOPLASTICS

Can be repeatedly softened by heat and hardened by cooling.

Reason: they are composed of linear and long chain molecules. application of heat weakens the intermolecular bonds by increasing thermal agitation of the molecules and hence the material softens.

Cannot use at high temperatures as they will soften under heat.

Usually supplied as granular materials.Comparatively software and less strong.

APPLICATIONS

Toys, combs, toilet goods, photographic films, insulating tapes, hoses, electric insulation

EXAMPLESPolystyreneAbsMethacrylatePVCPolycarbonatePolychoroacetal

DISADVANTAGES OF USING PLASTICS

Low strengthLow useful temperature range (up to 600 oF)Less dimensional stability over period of time

(creep effect)Aging effect, hardens and become brittle over timeSensitive to environment, moisture and chemicalsPoor machinability

LATEST DEVELOPMENTS

Bullet Proof Polymer - Scientists at Rice University, Texas have created a new super polymer material that can stop a 9mm bullet and seal the hole behind it.

The material is a complex multiblock copolymer polyurethanem, which is a synthetic compound build in the lab.

 

Plastics Blood - Developed by the University of Sheffield to mimic haemoglobin, for use in trauma situationswhere blood is needed quickly

The "plastic" blood consists of an iron-containing porphyrin which is permanently bonded to a hyperbranched polymer (HBP or dendrimer) "shell"

Plastic Solar Cells - A polymer solar cell that can produce electricity from sunlight by the photovoltaic effect provides a lightweight, disposable and inexpensive alternative to traditional solar panels

PET –polyethylene terephthalateITO – indium tin oxide

Implantable Polymers - Medical grade and implantable biomaterials such as PEEK will be used in neurological applications to help control epilepsy, Parkinson’s d.

Commercial - Space Flights Lightweight carbon composite materials will be crucial in the realisation of sub-orbital tourist spaceflightsisease and brain trauma

3D Printed - Body Parts Using plastic materials such as PMMA car parts can be printed at home and doctors can produce replica livers or kidneys for transplant patients.

Flexible Plastic Screens - Organic light-emitting diodes are placed on plastic foil to create electronic devices with flexible displays.

THE FUTURE

The future (2022) - The 2022 FIFA World Cup Qatar Showcase Stadium has been designed to use super reflective, triangulated PVC fabric to create a zero carbon, sustainable stadium providing comfortable playing conditions

THANK YOU