Composites & Processing techniques

composite

has continuous or matrix phase (polymer) surrounded by a discontinuous/dispersed phase (a filler, often times a fiber)

composites can be much ____________, __________, and less __________ than the original polymer

stronger / lighter / expensive

what is the continuous or matrix phase in a composite?

polymer

what is the discontinuous/dispersed phase in a composite?

filler, often a fiber

common example of composite

fiberglass

fiberglass

• composite

• glass fibers are filler and a thermosetting polymer, like an epoxy, is the matrix

• used in boats (kayak hull), hunting arrows, golf club shafts

in fiberglass (a composite), what is the filler and what is the matrix?

filler = glass fibers

matrix = thermosetting polymer (like epoxy)

most wwidely used processing technique

molding

what kind of materials does molding make?

sheet-like, foamed, hollow, or solid

3 types of molding

1. injection molding

2. blow molding

3. thermoforming

injection molding is used for many ___________ and some __________ (when using pre-polymer solutions)

thermoplastics / thermosets

injection molding

• force/inject molten polymer into a mold where it cools, becoming solid

• mold separates to release the object and then is put back together to repeat the process

• additives can be included in the molten polymer before injection

how are additives incorporated in injection molding?

included in molten polymer before injection

injection molders are _________ so you can use one machine to mold many different polymers into many parts

versatile

parts of a molder

1. hopper

2. heated cylinder

3. screw (for extrusion) or plunger

4. mold

purpose of screw or plunger in molder

injects polymer into the mold

molding __________ are fed into the hopper

pellets/beads

what part of a molder melts the polymer pellets/beads?

heated cylinder

what part of the molder physically injects the polymer?

screw/plunger

oftentimes, the little dot on the bottom of a piece of plastic is where …

the polymer was injected

larger parts are often made by _______ molding

reaction injection

RIM

• Reaction Injection Molding

• polymerization rxn occurs in the mold

• ex. automobile dashboards (poly(urethane))

in molding, the applied stress of the injection forces the polymerchains to _______ when flow rate is high enough

align

describe polymer layers formed in injection molding starting with layer directly on mold

1. amorphous (cold mold causes disorder)

2. crystalline (touching warmer polymer, aligned from high flow rate)

3. amorphous middle (cools slowly, chains can move)

blow molding

polymer is injected into a mold, and then air or some other gas is blown in to push the polymer against the sides

• good for making hollow objects like bottles

what type of processing would you use to make a bottle?

blow molding

sometimes in blow molding, you make a ________ or ________ first before blow-molding it in a later step

pre-formed / parison

many soda bottles are made from small ________

preforms

steps of thermoforming

1. heat a sheet or film of plastic above its Tg or Tm

2. stretch against a rigid mold

3. cool and trim

thermoforming is really useful for making ________ items

thin

what helps stretch the film against the mold in thermoforming?

vacuum

products made from thermoforming

• polystyrene: disposable cups, egg cartons

• ABS: boat parts

• HDPE: picku truck liners, golf cart tops, sleds

• multilayer materials for stay-fresh food packaging (ex. 2 layers of chip bag)