Plasticisers Flexibilisers

In order to increase the flexibility, and usually, in consequence, the toughness of the resins, plasticisers and flexibilisers may be added. Non-reactive plasticisers such as the conventional phthalates and phosphates have proved unsuccessful. Monofunctional materials, which in some cases also act as reactive diluents, have been used but are not of great importance. 

Ethylene copolymers (high molecular weight flexibilisers) have been proposed to replace liquid plasticiser for low smoke FR PVC cable formulations (238). 

Examples of other plasticisers are an adduct of tetrahydrofurfural alcohol and ethylene oxide and the reaction products of ethylene glycol either with organic acids or with anhydrides. Polyols and natural and synthetic rubbers are examples of flexibilisers. 

Epoxy resins produced by the reaction of bisphenol A and epichloro-hydrin are versatile polymers with several useful properties (subsection 2.2.2.1). However, one significant weakness is their brittle nature. Incorporation of plasticisers is not very useful. Dibutyl phthalate is an exception, showing good compatibility but offering only limited ability to flexibilise the resin. Moreover, plasticisers affect the mechanical properties and chemical resistance of the cured system. With polyurethanes it is possible to complement the flexibility of the epoxy system. Numerous attempts have been made to combine the two types to achieve beneficial modifications (Lee and Nivelle, 1967). These modifications proved successful under high-temperature cure but inferior results were obtained for ambient cures. 

Plasticisers (flexibilisers) Increasing flexibility, reducing melt temperature, lowering viscosity ... 

Pure PVC is thermally and photochemically unstable and has a tendency to lose hydrogen chloride when heated, hence a stabiliser (based on tin, lead, or other heavy metals) is commonly used. Pure PVC is also brittle and needs a plasticiser to soften and flexibilise the system. 

PVC dominates most of the literature on external plasticisers, mainly phthalate esters of Cg to Cjo, used to flexibilise PVC indoors flooring products to make them easy to roll, store and install. Some external plasticisers have high and low volatilities, but they are mostly toxic and ECD agents [17], and there is the probability that they will be emitted... 

Although there are many potential plasticisers, the requirements that have to be met for successful use are numerous. As a result, there are only about 100 commercially used plasticisers, with a further 200 known candidates that for various reasons are not currently used industrially. Several mechanical, optical and electrical properties of the flexibilised polymer... 

Even though there are literally hundreds of different epoxide resins and hardeners commercially available, giving countless formulations with a diversity of cured properties, further modifications of a material are sometimes still required. These modifications can be achieved by incorporating a range of compounds known as diluents, flexibilisers and plasticisers into the epoxide resin system during the formulation process. The properties of some typical diluents, flexibilisers and plasticisers are now discussed. 

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