Chapter 1 - Plastics Flashcards
What are plastics?
plastics are made of long chains of molecules. a large proportion of them are known as hydrocarbons
plastics can be grouped into 3 groups; thermoplastics, thermosets and elastomers
sources of plastics?
animal and vegetable by-products e.g. cellulose is a natural material occurring in plant fibres
General Properties
polymers are good electrical and thermal insulators
polymers have a good strength to weight ratio
generally polymers have a good atmospheric and chemical corrosion resistance
additives
fillers - used to reduce the bulk of the plastic
flame retardants - reduces the risk of combustion
anti static agents - reduces the effects of static charges
plasticiser - used to improve the flow properties of plastics
stabilisers - reduces the effect of ultraviolet light
biodegradable polymers
conventional polymers do not break down easily, biodegradable polymers are used in packaging, shopping bags, bottles and disposable items
PHAs and PHBs
also known as Biopol, PHAs are harvested from bacteria. PHB has similar properties to polypropylene whereas PHAs are used in the medical field
oxo-degradable polymers
these have additives that promote short degradation times. the additive ‘bio-batch’ can be used in conventional polymers
water-soluble polymers
e.g. detergent pouches. more expensive that conventional polymers.
processing plastics
insert picture.
injection moulding
insert picture. recognised through a complex 3-D shape and injector pin marks.
blow moulding
insert picture. recognised through being hollow at one end and sealed at the other. neck is smaller than the main body. sprue marks.
rotational moulding
insert picture. recognised through lack of sprue, hollow.
thermoforming
insert picture. recognised through sides being thinner than the base (due to stretching of sheet material)
