PLASTIC ADDITIVES BY D.Surendra,Lecturer in chemistry, D.K.W(A),G.D.C,Nellore VI Sem, Polymers (Cluster A)

Additives Any substance that is added generally in small concentration to resins in order to: Alter their properties Facilitate their processing Change the physical, chemical or electrical properties of end products. Reduce the cost

Features of Plastic Additives Effectiveness in their function Stable under processing conditions Economic Compatibility with polymer Matrix-at molecular level Neither volatile nor extrude to the surface Neither bleed nor bloom Must have low vapour pressure at high temperature Non- hazardous, non-impart taste & colour

Types of Additives Fillers Plasticizers and softeners Lubricants and flow promoters Anti-aging additives Flame-retardants Colourants Blowing-agents Cross-linking agents Photo stabilizers and .Nucleating agents

Fillers Fillers are usually solid additives. To give the plastic better hardness, tensile strength, finish and work ability to the product. To reduce the combustibility and increase water resistance.

Classification of fillers Perticulate rubbery resins fibrous cork Inert & Reactive& non-reactive Laminar & Reinforcing Random Organic Inorganic

Organic fillers: cellulosic fillers-wood floor,cotton,paper pulp etc., carbonaceous fillers-carbon black and graphite. Inorganic fillers: mineral fillers-Asbestos, powdered-mica, talc, silicate clays etc., powdered metals-Iron,lead,copper and aluminium

Examples of fillers Air fillers- Foam, Porous and honeycomb plastics, expended polystyrene etc. Fillers in powder form: Phenoplasts, phenoliths and aminoplasts. Fiber filled plastics :Phenol resins, fiber glass materials etc. Filler in the sheet form: Hardened paper, cloth laminate,asbestos-cloth laminates and wood laminates,etc.

Plasticizers and softeners Plasticizers are generally cyclic or acyclic organic chemicals that are added to synthetic plastics and results. These are high boiling, low molecular weight, non –volatile liquids. Reduce internal friction between polymer chains.

Effect of plasticizers Easy melt Improve flexibility Increases softness and flexibility Improve process ability Alters softening point, tensile strength, elongation at break and impact.

Types of plasticizers A. Cyclic plasticizers :They are used in the manufacture of synthetic plastics and resins. Ex: Dibutyl phthalate,try cresyl phosphate,Dioctyl sebecate. B.Acyclic plasticizers:These are less compatible and are usually employed together with plastics. Ex:Adipic acid esters,Epoxidised esters,oleic acid esters

Lubricants and flow promoters To reduce friction between the material and the processing equipment(Adhessive forces) To reduce heat and wear between two surfaces either between the polymer molecules.(cohesive forces) Reduces thermal degradation of the polymer Modifies flow characteristics Homogeneous the polymer melt with other polymer additives. To prevent the plastic from sticking to the mould surface during processing.

Ex: Silicone fluids, metal soaps,hydrocarbon waxes,amine waxes,ester derivatives, Long chain esters,glyceryl monostearate,fatty acids and amides

Flow promoters Low molecular weight materials. Impact better flow properties to the polymer mix under processing conditions without effecting the main properties under service conditions. EX: Chlorinated polyethylenes, acrylate copolymers

Anti aging additives The properties of the most plastic materials change with time in an adverse manner. These changes are a result of structural modifications. Causes for structural modifications: oxidation Attack by ozone Dehydro chlorination UV attack

For controlling structural modifications certain anti aging additives are added to the polymer materials. These are Anti oxidants ----peroxide decomposers metal deactivators UV light absorbers Anti ozonants: Derivatives of Para phenylene diamine

Stabilizers against Dehydrochlorination: Ex: Alkali earth oxides,epoxy compounds etc. UV Absorbers:o-hydroxy benzophenones,o-hydroxy phenyl benzotriazoles and salycylates.

Flame Retardants Prevent combustion by - insulate - creating endothermic cooling reaction -coating the product Types of Flame retardants: 1.Additive flame retardants-mineral flame retardants 2.Reactive flame retardants –organo halogen,o-phosphorous EX: Antimony trioxides, chlorinated paraffins , bromine compounds, substances containing N, B , Si , P , Cl , Br etc.

Colourants Dyes (soluble in polymers) Impart brilliant transparent colour to clear plastics Inorganic &organic AZOS for brightness and clarity Pigments (insoluble in polymers) Inorganic- Titanium dioxide(white)cadmium sulphide(yellow orange) Organic-Bennzidese(yellow-orange),copper pthalocyanine(blue),aniline black(black).

Blowing agent Or Foaming agent It is a substance which is capable of producing a cellular structure via a foaming process in materials that undergo hardening or phase transition. Types: Physical blowing agents Ex: Nitrogen and carbon dioxide, inert gas –low cost, low boiling liquids chemical blowing agents Ex: Azodicarbonamide, Azonitriles-decompose on heating and produce free radicals.

Cross-linking agents Cross-linking or curing or vulcanizing agents are important and essential ingredients for the above composition in the formation of thermo set plastics and vulcanized rubber. Processing types Molecules which bridge two polymer molecules during cross-linking. Ex: sulphur, selenium -------- diene rubbers Formaldehyde--------- Phenolics Molecules which initiate cross-linking reaction. Ex: peroxides ------- poly esters

Molecules which purely catalytic in their reaction. Ex: Acids-- phenolic resins, Amines ---epoxides .Molecules which attack the polymer chain to generate active -cite. Ex: peroxides

Photo stabilization Photo stabilization is the retardation or elimination of the photodegradation of any polymer during storage, processing and performing conditions. Stabilizers are classified as Anti-oxidants UV Absorbers

1.Preventive anti-oxidants----to prevent generation of radicals Anti-oxidants :protect the polymer from degradation by oxygen attack (oxidative degradation) These are two types 1.Preventive anti-oxidants----to prevent generation of radicals Ex: peroxide decomposers- Dilauryl thioprpianate, P-substituted phenyl phosphate Metal deactivators------Anti ozonants, wax additives 2.Chain-breaking anti-oxidants----these are interrupt the propagation of oxidative chain degradation. Ex: Styrenated phenols,phenyl napthylamines

UV Absorbers: These interact with the bfirst step of the photo oxidation process. Absorbs the harmful uv radiations before it reaches to the photo active chromophoric species in the polymer molecule. Hence, energy dissputes in the manner that does not lead to photosensitization. A uv absorber should be light stable, non-toxic and chemically inert. Ex: Phenyl salycilate,2,4-hydroxy benzophenone etc.

Nucleating agents Nucleating agents increase the rate of crystallization. Promote the formation of more spherulites. Enhanced properties such as flexural modulus and heat deflection temperature. Improved moulding productivity of polymer Increased transparency of polymer. Ex: Sodium, potassium, lithium benzoates Inorganic powders- clays, silica flour etc.

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