Lec 12 - ENGR ENGR 4250 Advanced Materials Engineering...

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ENGR 4250 ENGR 4250 – Advanced Materials Engineering Lecture 12 Applications & Processing of Polymers And COMPOSITES
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Molecular Weight Very long chains Not all chains are same length Average molecular weight i i n M x M = i i w M w M =
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Degree of Polymerization, n n = number of repeat units per chain CCCCCCCC H HHHHHHHH CCCC HHHH H () n i = 6 HHHHHHHHHHHH w n M M = = = i i w i i n m n w n m n x n m = unit repeat of weight molecular average where
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Molecular Structures • Covalent hain onfigurations and strength: Covalent chain configurations and strength: secondary bonding Direction of increasing strength Branched Cross-Linked Network Linear Adapted from Fig. 14.7, Callister 7e.
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End to End Distance, r Adapted from Fig. 14.6, Callister 7e.
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Polymer Crystallinity Polymers rarely 100% crystalline Too difficult to get all those chains aligned rystallinity of material crystalline region % Crystallinity : % of material that is crystalline. -- TS and E often increase ith % crystallinity with % crystallinity. -- Annealing causes crystalline regions to grow. % crystallinity increases. Adapted from Fig. 14.11, Callister 6e. amorphous region pg , (Fig. 14.11 is from H.W. Hayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials , Vol. III, Mechanical Behavior , John Wiley and Sons, Inc., 1965.)
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Amorphous Polymer
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Load vs Time Elastic Visco-elastic Viscous
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Time Dependent Deformation Stress relaxation test : -- strain to ε ο and hold. Data: Large drop in E r for T > T g . (amorphous -- observe decrease in stress with time. nsile test polystyrene) Adapted from Fig. 15.7, Callister 7e . (Fig. 15.7 is from .V. Tobolsky, 10 3 0 10 5 rigid solid (small relax) transition gion E r (10s) in MPa strain tensile test ε o A.V. Tobolsky, Properties and Structures of Polymers , John Wiley and Sons, Inc., 1960.) 10 1 10 -1 10 -3 region viscous liquid (large relax) Relaxation modulus : Sample T g ( ° C) values: time σ ( t ) 60 100 140 180 T (°C) T g o r t t E ε σ = ) ( ) ( PE (low density) PE (high density) PVC S -110 -9 0 + 87 100 Selected values from Table 15.2, Callister e PS PC +100 +150 7e .
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Relaxation Modulus r t t E σ ) ( ) ( = o ε
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Relaxation Modulus
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Barrier Properties
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Multi Layered Packaging
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Polymer Additives (15.21) Fillers lasticizers Plasticizers Stabilizers (against UV & Oxidation) Lubricants Colorants Flame retardants
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Polymer Additives Improve mechanical properties, processability, durability, etc.
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This note was uploaded on 10/18/2010 for the course ENGR 3360 taught by Professor Ahmadbarari during the Fall '10 term at UOIT.

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Lec 12 - ENGR ENGR 4250 Advanced Materials Engineering...

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