j3022 Chapter 12

CHAPTER 12 : PLASTIC (Plastik)

MATERIALS TECHNOLOGY 1 J3022

PREPARED BY : LIM YEE KAI

DEPARTMENT of MECHANICAL ENGINEERING

12.0 Introduction•Monomer : A molecule that can combine with others to form a polymer

•Polymers : are a large class of materials consisting of many small molecules (called monomer) ) that can be linked together to form long chains (polymerization), thus they are known as macromolecules . Polymer are a group of organic, semiorganic or inorganic.

•Plastic : Polymer that have been or can be readily formed or molded into a useful shape.

Monomer

ResinPlastic

Polymer

12.2 Classification Of Polymer

12.3 Polymer Structure Polymers are large molecules with strong intermolecular forces

and tangled chains Crystalline and semi-crystalline have an arrangement of their

chains that comes from packing Crystal region strengthen the polymer The percentage of the polymer that is crystalline is called the

percent crystallinity, has an important influence on the properties of the polymer.

Degree of crystallinity depends on the density.

12.5 Polymerization (Proses Pempolimeran) POLYMERIZATION: POLYMERIZATION: FForming large molecules from small

molecules OR the process by which polymers are formed. Types: Types: Additional & Condensation PolymerizationAdditional & Condensation Polymerization

12.5.1 Additional Polymerization12.5.1 Additional Polymerization (Polyaddition or chain growth polymerization) Definition:Definition: *A polymerization technique where

monomer molecules add on to a growing polymer chain one at a time.

The monomers quickly combine by an addition

reaction without losing any atoms, so that the polymer has the same basic formula as the monomer.

nM ----> -(-M-)n-

(monomer) (polymer)

12.5.1 Additional Polymerization12.5.1 Additional Polymerization (Continued)

Vinyl polymers are addition polymers, which have the same atoms as the monomer in their repeat units.

12.5.2 Condensation Polymerization 12.5.2 Condensation Polymerization ((step-reaction polymerization)

Definition:Definition: *Covalent bonds are rearranged in such a

way that two monomers are connected and water is "condensed" out.

12.5.2 Condensation Polymerization 12.5.2 Condensation Polymerization (Continued)

A few types of condensation polymers are listed below. In the table, R and R' stand for organic groups.

12.6 Types of Polymer

Thermoplastics Thermoset plastics1. Addition polymerization.

2. Softens on heating and retaining the same

chain on cooling.

3. They are along chain linear polymers

without any branched or cross linked chain.

4. On repeated heating and cooling, there is no

change in chemical nature.

5. These plastics undergo purely physical

process.

6. By heating the plastics, they can be proceed.

7. Waste thermoplastics can be recovered.

1. Condensation polymerization.

2.Heat resistance.(infusible and insoluble

mass on heating )

3. They are branched or cross-linked

Polymer.

4. Some sort of chemical changes occur

On heating.

5.These Plastics undergo physical as well

as chemical process.

6. These plastics cannot be proceed by heating.

7. Waste thermosetting cannot be recovered.

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12.6.1 Thermoplastic (cont…)

Polyethylene (PE) Clear to whitish translucent thermoplastic.

LD: low glass transition temperature, Tg (very attractive), used for plastic bags, coatings, and squeeze bottles.

HD: more crystalline linear polymer with improved strength, stiffness, and chemical inertness.

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Polyethylene (PE) Types

Low density (LDPE)

High Density (HDPE)

Linear low density (LLDPE)

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Polyethylene (PE)Applications: containers, insulation, chemical tubing, bottles, water pond liners etc

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Polyvinyl Chloride (PVC) PVC is amorphous, does not recrystallize. PVC homopolymer has high strength (7.5

to 9 ksi) and is brittle. Compounding of PVC: Modifies and

improves properties. Application: Clothing, Electric wires, Pipes,

Portable electronic accessories, Signs, Joining, Ceiling tiles, Unplasticized polyvinyl chloride (uPVC)

Products of PVC

PVC pipes, fittings, flexible hoses and gaskets

PVC CementPVC Ceiling Tiles

Credit card

PVC Products

PVC footwear PVC costume PVC car sticker & decal

PVC sign

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Polypropylene (PP)

Isotactic form is crystalline and has the most applications

Higher strength and stiffness than PE. High melting (165-1770C)and heat deflection

temperature. Low density, good chemical resistance, moisture

resistance , heat resistance, good surface hardness and dimensional stability.

Applications: Useful in many application involving boiling water or steam, house wares, appliances, packaging, laboratory ware, bottles, etc.

Product of PP

Document Boxes & PP Folders

PP knife handlePP rope

OPP Tape

PP ChairToys

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12.6.1 THERMOPLASTIC (cont…)

Polystyrene (PS) Transparent, brittle and chemically inert By heating polystyrene with a foaming agent,

expanded polystyrene can be made. Expanded beads create excellent thermal insulation properties (Styrofoam).

Styrofoam is extremely light, white solid foam. It mainly used to make light-weight ceiling tiles in buildings, and food boxes and shock absorbers for packaging.

Polystyrene (PS) continue…..

Poor weatherability and easily attacked by chemicals.

Low processing cost and good dimensional stability.

Applications: Automobile interior parts, dials and knobs of appliances and housewares

1939: Wood TV Cabinet 1948: Phenolic TV Cabinet 1970: HIPS TV Cabinet

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Polymethyl Methacrylate (PMMA)/ Acrylic

Rigid and relatively strong. Completely amorphous and very

transparent. Good outdoor weatherability and is

more impact-resistant than glass. An acrylic commonly known as

Plexiglas. Applications: Glazing of aircraft,

boats, skylights, advertising signs etc.

Automotive lamps

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Polyamides (PA) High strength due to hydrogen bonding between

molecular chain Flexibility of carbon chain contributes to molecular

flexibility, low melt viscosity and high lubricity.

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12.6.1 THERMOPLASTIC (cont…)

Tough, opaque solids with moderate melting points. Outstanding characteristic is the ability to draw into

fibers, becoming tough, transparent materials of relatively high strength.

High strength, toughness and dimensional stability. Very high impact strength. High heat deflection temperature. Engineering applications:

Widely used in the textile industry: Armor, personal protection, sport equipment.

Audio equipment, drumheads woodwind reeds. Others used: rope, cable, sheath, electricity generation,

building construction, brakes, expansion joints and hoses, composite material.

Products of Polyamides (PA)

Kevlar Ballistic vestsInner lining of tubeless tyres

Reinforcing composite materials (combination with carbon fiber, glass fiber) used in body of gitar, cricket bats, boat.

Nylon Stocking

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12.6.1 THERMOPLASTICThermoplastic Polyesters Primarily used as fibers and films with the most

important being polyethylene terephthalate (PET) Phenylene ring provides rigidity

Good insulator: independent of temperature and humidity.

Applications: Switches, relays, TV tuner components, circuit boards, impellers, housing and handles

Products of Polyester

Photographic film

polyester cellophane tape

Polyester backpack

Polyester tie

Men’s polo T-shirt

Polyester sarees100% Polyester Coral Short Robes

Polyester pants

Recycle Polyester

recycled polyester fiber

On July 20, 1969 – the human race accomplished its greatest technological achievement of all time when Neil Armstrong set foot on the moon. This feat would not have been possible without many materials science developments. Plastics played an important roll. For example, the Apollo A7L space suits were a multi-layer plastic structure comprised of nylon fabric, neoprene coated nylon fabric, Dacron® (PET) fabric, aluminized Mylar® (PET) film, Kapton® (PI) film, and Teflon® (PTFE) coated fabric. The “fish bowl” helmet was produced from transparent polycarbonate. The space suits of today make even more extensive use of plastics.

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12.6.2 Thermosets (cont…)

Epoxy Resins Good adhesion, chemical resistance and

mechanical properties

High molecular mobility, low shrinkage during hardening

Applications: Protective and decorative coating, drum lining, high voltage insulators and laminates

Commercial/Industrial Epoxy Floor Coating

(a) (b) (c)

Products of Epoxy

Epoxy printed circuit board (PCB)

Double-Sided Printed Circuit Boards (PCBs)

Epoxy Surfboards

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Phenolics Low cost, good insulating and mechanical properties. Produced by polymerization of phenol and

formaldehyde. General purpose compounds: Usually wood flour

filled to increase impact resistance. High impact strength compounds: Filled with

cellulose and glass fibers. High electrical insulating compounds: Mineral (Mica)

filled. Heat resistant compounds: Mineral filled. Applications: Wiring devices, auto transmission

parts, plywood lamination, adhesives, shell molding.

Products of Phenolics

Bakelite letter opener

Bakelite radioBakelite pool ball

Phenolic Plywood

1948: Phenolic TV Cabinet

Cookware with phenolic handle

Melamine Application: Molded dinnerware, buttons,

control buttons, & knobs

Melamine dinnerware Melamine Faced MDF / Chipboard

Melamine Milk

Staff members of the local quality supervision bureau empty melamine tainted milk powder packets at a garbage dump site in Shenzhen

Which companies are affected?

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Polyurethanes (PU) Primarly used as faoms Depending on cross-linking, urethanes may

behave as thermosets, thermoplastic, or elastomers

Application include Fibers Coatings Foams for furniture Mattresses Insulation Packing or shipping material

Products of Polyurethanes (PU)

PU foams

In-line skate wheels

PU foodbed and midsole

Products of Polyurethanes (PU)

PU condom

Cool room PU panelPU panel

PU Foam

Plastic Moulding

Extrusion Moulding

Injection Moulding

Blow Moulding

Transfer/Compression Moulding

Extrusion Blow Moulding

Injection Blow Moulding

Stretch Blow Moulding

Pengacuanan Penyemperitan

Pengacuanan Penyuntikan

Pengacuanan Pindah/Mampatan

Pembentukan Bahan Plastik

Stretch Blow Moulding

Pengacuanan Peniupan

Extrusion Moulding (Pengacuanan Penyemperitan)

- Feed section- stock comes in from hopper and preheated,

- Compression section- resin transformed into liquid form, entrapped air forced out via compression

- Metering section- homogen melt, sufficient pressure to pump through the die.

Injection Moulding (Pengacuanan Penyuntikan)

This schematic illustrates the basics of plastic injection molding system.

A hot, molten polymer is injected into a cold mold. A screw apparatus can be used to inject the polymer into the

mold. After the part is solidifies, the mold is opened and part is

ejected.

Cycle Time of Injection Moulding Machine

Injection Moulding is a CYCLIC process:• Injection: polymer is injected into the mold cavity• Hold on time: once the cavity is filled, a holding pressure is maintained to

compensate for material shrinkage• Cooling: the molding cools and solidifies.• Screw Back: at the same time, the screw retracts and turns, feeding the next shot

in towards the front.• Mold Opening: once part is sufficiently cool, the mold opens and the part is ejected• The mold closes and clamps in preparation for another cycle.

Test Your Understanding

Plastic model

Products of Injection Moulding

Compression Moulding Compression molding is an old and widely used molding

process for thermosetting plastics. Its applications also include thermoplastic phonograph

records, rubber tires, and various polymer matrix composite parts.

Materials for compression molding include phenolics, melamine, urea-formaldehyde, epoxies, urethanes, and elastomers. Typical TS plastic moldings include electric plugs, sockets, and housings; pot handles, and dinnerware plates.

The process, consists of: (1) loading a precise amount of molding compound, called the charge, into the bottom half of a heated mold.(2) bringing the mold halves together to compress the charge, forcing it to flow and conform to the shape of the cavity(3) heating the charge by means of the hot mold to polymerize and cure the material into a solidified part.(4) opening the mold halves and removing the part from the cavity.

Compression MouldingCompression MouldingAdvantages molds that are simpler, less expensive, and

require low maintenance less scrap low residual stresses in the molded parts

(thus favoring this process for flat thin parts such as phonograph records).

Disadvantages longer cycle times and therefore lower

production rates than injection molding.

Injection Blow Moulding Process

2 different process. Parison formed from injection blow moulding system is called a

preform. It is not a finished part but subjected to subsequent steps that

forms the final shape. Proven to be economical.

Extrusion Blow Moulding In Extrusion Blow Molding

(EBM), plastic is melted and extruded into a hollow tube (a parison).

This parison is then captured by closing it into a cooled metal mold.

Air is then blown into the parison, inflating it into the shape of the hollow bottle, container or part.

After the plastic has cooled sufficiently, the mold is opened and the part is ejected.

Stretch Blow Molding

Plastic is first molded into a "preform" using the Injection Molded Process. These preforms are later fed (after cooling) into an EBM blow molding machine. In the SBM process, the preforms are heated (typically using infrared heaters)

above their glass transition temperature, then blown using high pressure air into bottles using metal blow molds.

Usually the preform is stretched with a core rod as part of the process. The stretching of some polymers, such as PET (PolyEthylene Terepthalate)

results in strain hardening of the resin, allowing the bottles to resist deforming under the pressures formed by carbonated beverages, which typically approach 60 psi.

Blown Film Extrusion

Plastic pellets are fed and melt in the extruder. Resin enters annular die and forced inside a mandrel where it is shaped into

sleeves, extruded into a die opening in form of thick walled tube. Using pressure of internal air introduced from center of mandrel, molten tube

will expend into “bubble” of desired diameter and lower the film thickness. Air is maintained at constant pressure. Nip rollers are used to collapse the “bubble”, stretch the film and serve as take-

off device for the line.

Blown Film Extrusion

REFERENCESWilliam D.Callister, Jr, Materials Science and Engineering an Introduction, 2003, 5th edition,John Wiley & sons,Inc.Smith W.F & Hashemi J. (2004) Foundation of material science and engineering third edition. NY:McGraw-Hill Company, inc.Serope Kalpakjian and Steven R. Schmid, Manufacturing Engineering and Technology, 2001, 4th edition, Prentice Hall,Inc.

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j3022 Chapter 12