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PRODUCTION TECHNIQUES(MANUFACTRING PROCESSES)

ACADEMIC YEAR 94-95, SEMESTER ONE

PROCESSING OF POLYMERS

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Chapter 7Polymers: Structure, General Properties and Applications

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Polymers Polymers and Plastics Plastics are one of numerous polymeric materials and have

extremely large molecules (macromolecules or giant molecules)

Consumer and industrial products Replacing for metallic components in applications such as

automobiles, civilian and military aircraft, sporting goods, toys and so on because of their unique and diverse properties

Polymers characteristics Corrosion resistance and resistance to chemicals Low electrical and thermal conductivity Low density High strength-to-weight ratio (particularly when reinforced) Noise reduction Wide choice of colors and transparencies Ease of manufacturing and complexity of design possibilities Relative low cost Low strength and stiffness High coefficient of thermal expansion Low useful-temperature range- up to 350°C Lower dimensional stability in service over a period of time

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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Mechanical Properties of Engineering Plastics

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Structure of Polymer Molecules

Figure 7.2 Molecular structure of various polymers.

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Polymerization

Figure 7.3 Examples of polymerization. (a) Condensation polymerization of nylon 6,6 and (b) addition polymerization of polyethylene molecules from ethylene mers.

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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

The Effect of Molecular Weight and Degree of Polymerization on Polymers

Figure 7.4 Effect of molecular weight and degree of polymerization on the strength and viscosity of polymers.

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Polymer Chains

Figure 7.5 Schematic illustration of polymer chains. (a) Linear structure – thermoplastics such as acrylics, nylons, polyethylene, and polyvinyl chloride have linear structures. (b) Branched structure, such as in polyethylene. (c) Cross-linked structure – many rubbers or elastomers have this structure, and the vulcanization of rubber produces this structure. (d) Network structure, which is basically highly cross-linked – examples are thermosetting plastics, such as expoxies and phenolics.

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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Behavior of Polymers

Figure 7.6 Behavior of polymers as a function of temperature and (a) degree of crystallinity and (b) cross-linking. The combined elastic and viscous behavior of polymers is known as viscoelasticity.

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Amorphous and Crystalline Regions in a Polymer

Figure 7.8 Amorphous and crystalline regions in a polymer. The crystalline region (crystallite) has an orderly arrangement of molecules. The higher the crystallinity, the harder, stiffer, and less ductile the polymer.

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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Volume of Polymers as a Function of Temperature

Figure 7.9 Specific volume of polymers as a function of temperature. Amorphous polymers, such as acrylic and polycarbonate, have a glass-transition temperature, Tg, but do not have a specific melting point, Tm. Partly crystalline polymers, such as polyethylene and nylons, contract sharply while passing through their melting temperatures during cooling.

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Glass-Transition and Melting Temperatures of Polymers

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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Types of Plastics

Figure 7.10 General terminology describing the behavior of three types of plastics. PTFE (polytetrafluoroethylene) has Teflon as its trade name. Source: After R.L.E. Brown

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Effect of Temperature on the Stress-strain Curve for Cellulose Acetate

Figure 7.11 Effect of temperature on the stress-strain curve for cellulose acetate, a thermoplastic. Note the large drop in strength and the large increase in ductility with a relatively small increase in temperature. Source: After T.S. Carswell and H.K. Nason.

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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Effect of Temperature on Plastic Impact Strength

Figure 7.12 Effect of temperature on the impact strength of various plastics. Small changes in temperature can have a significant effect on impact strength. Source: After P.C. Powell

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Plastic Product Recommendations

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Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Thermoplastic Polymer Trade Names

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Load-Elongation Curve for Rubbers

Figure 7.14 Typical load-elongation curve for rubbers. The clockwise loop, indicating the loading and the unloading paths, displays the hysteresis loss. Hysteresis gives rubbers the capacity to dissipate energy, damp vibration, and absorb shock loading, as is necessary in automobile tires and in vibration dampers placed under machinery.