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lecture 4 - Coggle Diagram
lecture 4
additives in plastics
to impact certain specific properties, polymers are compounded with additives
plasticizers are added to polymers to impart flexibility and softness by lowering glass-transition temperature
:stabilizers: ultraviolet radiation and oxygen which weaken and break the primary bonds which cause polymer degrades and becomes stiffer and brittle
fillers improve strength, toughness, hardness, abrasion resistance, dimensional stability
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lubricants added to reduce friction during subsequent processing into final products. also they prevent parts from sticking to the molds
thermosetting plastics
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curing(cross-linked)reaction, unlike that of thermoplastics, is irreversible
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1- in chemical plant, molecules are partially polymerized onto linear chain
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elastomers (rubbers)
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hardness of elastomers increases with the cross-linking of the molecular chains (e.g vulcanization of rubber with sulfur)
hysteresis loss in stretching and compression gives the rubber the capacity to dissipate energy, damping vibration and absorb shock load
natural rubber
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has good resistance to abrasion and fatigue, and high friction, low resistance to oil, heat, ozone and sunlight
synthetic rubber
have better resistance to heat, gasoline, and chemicals, higher range of useful temperatures
biodegradable plastics
biodegradability means that microbial species in the environment will degrade a portion of polymeric material under proper environmental conditions
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biodegradability will divert attention from recycling plastics and conservation of material and energy
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