Internal plasticisation

Whilst vinyl acetate is reluctant to copolymerise it is in fact usually used today in copolymers. Two of particular interest to the plastics industry are ethylene-vinyl acetate (Chapter 11) and vinyl chloride-vinyl acetate copolymers (Chapter 12). In surface coatings internal plasticisation to bring the Tg to below ambient temperatures and thus facilitate film forming is achieved by the use of ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate and dialkyl maleates and fumarates. 

The volumetric, elastic and dynamic properties of internally and externally plasticised PVC were studied and compared with those of unplasticised PVC. The glass transition temperature for the plasticised samples was markedly lowered and this decrease was more important for the externally plasticised ones. The positions of the loss peaks from dielectric alpha-relaxation measurements confirmed the higher efficiency of the external plasticisation. However, the shape of the dielectric alpha-relaxation function was altered only for the internally plasticised samples. The plasticisation effect was linked with a decrease in the intensity of the beta-relaxation process but no important changes in the activation energy of this process were observed. The results were discussed. 47 refs. 

The purpose of plasticisation is to decrease hardness and to increase flexibility and elongation. Phthlates (e.g. butyl benzyl phthalate, dioctyl phthalate and butyl phthalate) are used as external plasticisers. Externally plasticised systems have a migratory tendency with ageing. In order to overcome this drawback, systems are being internally plasticised. This process involves the use of comonomers (e.g. acrylates and higher alkyl... 

Internally plasticised acrylic systems are more common in today s market. Such systems have greater long-term flexibility which in turn provides durability to the coating. 

The cardol present in CNSL, if in high proportion can lead to an exothermic reaction with formaldehyde and also It appears desirable for the phenolic components to have a high proportion of triene in order for the first acid-catalysed side chain oligomerisation stage to proceed. CNSL-formaldehyde polymers have greater flexibility than those from phenol-formaldehyde, due to internal plasticising, they are also more soluble in solvents, and due to their hydrophobicity they have resistance to water penetration, and hence acidic and alkaline media. For some applications highly methylolated cardanol is useful and this can be formed with formaldehyde, by the use of adipic or succinic acid as catalysts, and subsequently rapidly cured with hexamine (ref. 245). 

A rigid polymer may be internally plasticised by chemically modifying the polymer chains with structural groups incorporated through a plasticising comonomer, which is a common way of plasticisation or it can be externally plasticised, simply by blending it with the resin. The latter being the most common because of the costs involved. UPVC (PVC-U) can be externally plasticised by use of certain phthalates. 

Plasticisation may occur either internally or externally. In some cases, plasticiser function can be obtained by copolymerising the polymer with the monomer of a low Tg polymer such as PVA, this process is called internal plasticisation, typical external plasticisation is addition of dioctyl phthalate, diisooctyl phthalate and di-2 ethyl... 

On the other hand, by the use of internal plasticisers where the plasticiser is incorporated (usually by grafting) onto the polymer chain of PVC (see Section 12.2.2.1)... 

One of the most common types of emulsion for decorative paint is based on vinyl acetate internally plasticised with about 20 parts of vinyl versatate. Di-butyl or di-octyl maleate or fumarate are also used as plasticising monomers for vinyl acetate, but butyl acrylate or 2-ethylhexyl acrylate are now preferred. Vinyl acetate homopolymers externally plasticised with di-butyl phthalate are still widely used. 

The MFFT of the emulsion as formulated must be lower than any tempoature at which the paint is likely to be applied. For an indoor paint in the UK it is unlikely that temperatures below 10°C will be encountered, whilst the outdoor limit might be 5°C. Damage to paint films can occur should the ambient temperature fall below the Tg of the film. The Tg of a hard polymer, such as vinyl acetate, styrene or methyl methacrylate, can be reduced either by copolymerisation with a soft monomer or by adding an external plasticiser, such as butyl phthalate. On a cost effective basis external plasticisation is better for reducing the Tg. The snags are, firstly, that plasticisers are slowly lost through evaporation and, secondly, they can also diffuse into the substrate. The use of an internally plasticised polymer overcomes both problems and also saves the processing time necessary to incorporate an external plasticiser. 

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