Polymeric impact modifiers and processing aids

Rubber Solubility parameter (MPa ) hod impact strength (ftlbf/in of notch) 

The anomalous effect of the last two rubbers in the table with their low solubility parameters is possibly explained by specific interaction of PVC with carbonyl and carboxyl groups present respectively in the ketone- and fumarate-containing rubbers to give a more than expected measure of compatibility. It is important to note that variation of the monomer ratios in the copolymers and terpolymers by causing changes in the solubility parameter and eompatibility will result in variation in their effect on impact strength. 

At one time butadiene-acrylonitrile copolymers (nitrile rubbers) were the most important impact modifiers. Today they have been largely replaced by acrylonitrile-butadiene-styrene (ABS) graft terpolymers, methacrylate-buta-diene-styrene (MBS) terpolymers, chlorinated polyethylene, EVA-PVC graft polymers and some poly acrylates. 

ABS materials are widely used as impact modifiers but cause opacity and have only moderate aging characteristics. Many grades show severe stress-whitening, generally a disadvantage, but a phenomenon positively employed in labelling tapes such as Dymotape. 

There are a number of applieations such as bottle and film where tough materials of high elarity are desired. The advent of MBS material has been a significant advance to meet the requirements. It has been found possible here to produce an additive with sufficiently different solubility parameters from the PVC for it to exist in the disperse phase but with a very similar refractive index to the PVC so that light scattering at the interface between the two phases is at a minimum. However, owing to differences in the formulation of PVC compounds, a particular MBS modifier may not have exactly the same refractive index as the PVC eompound. 

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Acrylics. Acetone is converted via the intermediate acetone cyanohydrin to the monomer methyl methacrylate (MMA) [80-62-6]. The MMA is polymerized to poly(methyl methacrylate) (PMMA) to make the familiar clear acryUc sheet. PMMA is also used in mol ding and extmsion powders. Hydrolysis of acetone cyanohydrin gives methacrylic acid (MAA), a monomer which goes direcdy into acryUc latexes, carboxylated styrene—butadiene polymers, or ethylene—MAA ionomers. As part of the methacrylic stmcture, acetone is found in the following major end use products acryUc sheet mol ding resins, impact modifiers and processing aids, acryUc film, ABS and polyester resin modifiers, surface coatings, acryUc lacquers, emulsion polymers, petroleum chemicals, and various copolymers (see METHACRYLIC ACID AND DERIVATIVES METHACRYLIC POLYMERS). 

Additives may be monomeric, oligomeric or high polymeric (typically impact modifiers and processing aids). They may be liquid-like or high-melting and therefore show very different viscosity compared to the polymer melt in which they are to be dispersed. 

Many polymeric plasticisers, impact modifies, and processing aids for PVC are incorporated into the PVC by mechanical mixing Many of these, including butadiene-acrylonitrile copolymers, ethylene-vinyl acetate copolymers chlori-... 

In addition to acting as impact modifiers a number of polymeric additives may be considered as processing aids. These have similar chemical constitutions to the impact modifiers and include ABS, MBS, chlorinated polyethylene, acrylate-methacrylate copolymers and EVA-PVC grafts. Such materials are more compatible with the PVC and are primarily included to ensure more uniform flow and hence improve surface finish. They may also increase gelation rates. In the case of the compatible MBS polymers they have the special function already mentioned of balancing the refractive indices of the continuous and disperse phases of impact-modified compound. 

Especially in recent years, there has been a tendency to develop stabilisers with higher-MW (>2000 Da) to prevent loss under severe conditions of application. Polymeric additives for polymers, including impact modifiers, flexibilisers, antistatic agents, and processing aids, have been reviewed [54]. 

A time-controlled polymeric system which would be environmentally friendly should present three phases in the transformation, (a) Very limited variation in useful properties corresponding to the induction period or to very slow chemical transformation. This phase is well controlled by the use of efficient stabilizers the role of additives in creating tailormade plastics and in generating long-term innovative products is commonly accepted. Stabilizers, sensitizers, pigments, lubricants, processing aids, impact modifiers and other... 

The dynamic mechanical behavior of most homogeneous and heterogeneous solid and molten polymeric systems or composite formulations can be determined by DMA. These polymeric systems may contain chemical additives, including fillers, reinforcements, stabilizers, plasticizers, flame retardants, impact modifiers, processing aids, and other chemical additives, which are added to the polymeric system to impart specific functional properties and which could affect the process-ability and performance. 

Rigid PVC is polymerized at 55-70°C and then compounded with organotin stabilizer, acrylic processing aid, lubricants, and optionally with rubbery impact modifier. 

A PVC compound may contain, besides the polymer, the following ingredients stabilizers, plasticizers, extenders, lubricants, fillers, pigments, and polymeric processing aids. Other ingredients also used occasionally include impact modifiers, fire retardants, optical bleaches, and blowing agents. 

Examination of the THF-ethanol-insoluble fraction. This will consist of the base polymer, which will usually be a PVC homopolymer but could be a copolymer of vinyl chloride (VC) with another monomer such as vinyl acetate (VA). Also present may be polymeric processing aids such as Paraloid K120N (90 10 methylmethacrylate ethyl acrylate copolymer), impact modifiers that are totally soluble in THF such as EVA or CPE, and impact modifiers that are partially soluble in THF such as nitrile rubber and SAN fractions from ABS. 

PVC offers a unique combination of properties. The great variety of its properties is achieved by the different polymerization processes, copolymerization with other polymerisates, and the use of processing aids, heat stabilizers, UV-stabilizers, lubricants, plasticizers, fillers, pigments, impact modifiers, postchlorination and others. 

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