Plastic Compounding

Mixing: By mixing we mean bringing into intimate contact of two or more components (mutually compatible or incompatible) and subjecting them to a shearing force so as to bring deformation in them and distribute them uniformly throughout the total volume to make the mass homogeneous. Compounding: By compounding we mean mixing ingredients such as plasticizers, vulcanizing agents, curatives, stabilizers, fillers, coloring agents, flame retardants and lubricants into the virgin resin in a specific proportion as per requirement, i.e. mixing the ingredients as per the recipe or formulation. Here, virgin resins of plastic materials mean polystyrene, polyethylene, polymethyl methacrylate, PVC and other polymers.

Physical Process involved in mixing and compounding: Different ingredients are brought into intimate contact. Subjected them to shear forces Deformation takes place resulting in increase in the interfacial area between the components. In the process, we can apply smearing(To apply by spreading or daubing: smeared lotion on my face and arms.), folding, stretching, wiping (To subject to light rubbing or friction, as with a cloth or paper, in order to clean or dry.), Striation (any of a number of tiny parallel grooves increase the surface area of the components , this surface get smeared with the other ingredients, when smeared layer passes another such layer, the smeared materials get wiped on to the second one. Entrapped materials within grooves.) - compression and shearing ------ all of these take place simultaneously throughout the mass.

Fillers: Fillers are added to impart special properties and reduce the finished product cost. Fillers may simply used as loading agents (particulate materials and fibrous materials). Particulate materials: Carbon-black, silica, wood flour etc. Fibrous materials: Glass fiber, cotton, wood pulp etc.

Plasticizers: are high boiling non-volatile organic compound or liquid Plasticizers: are high boiling non-volatile organic compound or liquid. Plasticizers used to reduce the modulus of a polymer. Increasing the concentration of plasticizer causes the transition from the high modulus (glassy) region to the low modulus (rubbery) region at lower temperature. Ex. Dioctyl phthalate and Tricresyl phosphate

Stabilizers: are used to protect the polymers from thermal, oxidative and photo-degradation. Antioxidant: protects the polymer against degradation by oxygen attack. (prevents the formation of free radicals and prevents the breaking of double or triple bond from chain breaking) ex: p- substituted phenyl phosphites UV-absorber: protects the polymer against degradation by ultra-violet light. ex: phenyl salicylate

Coloring agents: Contain inorganic pigments Coloring agents: Contain inorganic pigments. Various types and shades of pigments and dyes are used as coloring agents in polymer compounding. Colorants have high covering power Colorants should be stable under processing condition. It shows different degrees of solubility in the polymer matrix.

Lubricating and Flow promoters: Lubricating used to allow the quick mould release. Prevent the moulded object from sticking to the mould Reduce the surface friction at the interface Lubricants such as silicon fluids , graphite are used.

Cross-linking agents: It is used for all cross-linkable or curable composition leading to the production of thermo-set plastics and vulcanized rubber. (Cross-linking agents react with molecules and are coupled directly into the cured system as a structural member of the polymer.) Sulpher and peroxides, such as benzoyl peroxide is widely used as the curing agents (toughening or hardening of a polymer material by cross-linking).