Page 185 - C:\Users\Adik\Documents\Flip PDF Professional\Marketer PPT LR\

I) Internal Lubricants: They are highly compatible with the polymer and they
reduce the cohesive forces between the polymer molecules. These loosens one
chain from another, resulting in lower melt viscosity, better polymer flow and
maximum processing efficiency. e.g. PE and PP waxes.
ii) External lubricants: They are less compatible with the polymer and migrate to
the surface and provide slip or release between the polymer and the cylinder, mould
or die. E.g. Metal stearates, oxidised PE wax and fluoro elastomers.
Processing Aids: These additives are used to improve processability of plastics by
increasing flow and by reducing friction with the machine's metal parts. Processing
aids contain internal lubricants that improve the melt flow of material by lowering the
viscosity and heat dissipation.
Foaming / Blowing agents: An additive ingredient added to plastic to produce gas
by chemical or thermal action, or both, which results in hollow or cellular voids /
structures within the plastic article. Blowing agents decompose at elevated
temperatures forming gas and other inert components that expand the plastic
material, giving it a cellular structure. This process offers weight reduction, better
acoustical properties, better insulation as well as cost savings. Loading level are
normally in range of about 0.5% to 2.5% by weight of polymer and density
reductions of about 50 to 60% are common. These are further classified into
exothermic and endothermic foaming agents. Exothermic foaming agents are
usually used for larger parts while endothermic foaming agents can be used for
small parts and removal of sink marks in moulded parts. Two types of pore
structures are possible: open and closed cell.
Closed-cell plastics have discrete, self-contained pores which are roughly
spherical.
Open-celled plastics contain interconnected pores, allowing gases to pass through
voids in the plastic.
Azodicarbonamide (AZ) is widely used exothermic CFA. Endothermic CFAs are
usually blends of inorganic carbonates and polycarbonic acids that generate
carbon dioxide gas.
Impact modifiers: Enables plastic products to absorb shocks and resist impact
without cracking. A material such as rubber, an elastomer or some plastics with
excellent impact resistance, is blended with a resin to improve its impact resistance.
Eg: EPR, EPDM, Butadiene rubber and others. Particularly relevant for polyvinyl
chloride (PVC), polystyrene (PS) and polypropylene (PP) materials
Flow modifiers: When added in small quantities to the base resin reduces the melt
viscosity resulting in fast production rates.
Plasticizers: are additives that soften the materials (usually a plastic or a concrete
mix) they are added to, and are used for increasing its flexibility. It is generally used
to give hard plastics like PVC the desired flexibility and durability. Plasticizers work
by embedding themselves between the chains of polymers, space them apart
(increasing of the “free volume”), and thus significantly lowering the glass transition
temperature for the plastic and making it softer. Some plasticizers evaporate and
tend to concentrate in an enclosed space; the “new car smell” is caused mostly by
plasticizers evaporating from the car interior.

DAVE TECHNICAL SERVICES 185