Reactive impact modifiers

In order to obtain a finely sized dispersed phase in the PET matrix, the use of reactive compatibilization has been found to be important. Small dispersed rubber particles and a small interparticle distance are necessary to induce high toughness. For effective rubber toughening of PET, it is important that the rubber domains be less than 3 im in diameter (and preferably less than 1 xm) and that the interparticle distance be between 50-300 nm. 

Reactive impact modifiers are preferred for toughening of PET since these form a stable dispersed phase by grafting to the PET matrix. Non-reactive elastomers can be dispersed into PET by intensive compounding but may coalesce downstream in the compounder. Reactive impact modifiers have functionalized end groups. Functionalization serves two purposes - first, to bond the impact modifier to the polymer matrix, and secondly to modify the interfacial energy between the polymer matrix and the impact modifier for enhanced dispersion. Some examples of commercially available reactive impact modifiers for PET are shown in Table 14.3. An example of a non-reactive elastomer that can be used in combination with reactive impact modifiers is ethylene methyl acrylate (EMA), such as the Optema EMA range of ethylene methyl acrylates manufactured by the Exxon-Mobil Chemical Company (see Section 4.2). 

The chemical reaction between glycidyl methacrylate (GMA) end groups on the reactive elastomer and the carboxylic acid end groups of PET is shown in 

E-EA-GMA (67 25 8) (ethylene-ethyl acrylate-glycidyl methacrylate terpolymer) Lotader AX89006 Atofina 

E-BA-GMA (63 31 6) (ethylene-butyl acrylate-glycidyl methacrylate terpolymer) Elvaloy PTW DuPont 

E-VA-MA (ethylene-vinyl acetate copolymer, functionalized with maleic anhydride) Exxelor VA1803 Exxon 

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The future direction of polyester R D efforts is likely to involve further progress in polyester synthesis given the wide range of potential monomer combinations, new blending technology and the use of advanced functional additives such as nanoclay reinforcements, reactive impact modifiers, anti-hydrolysis agents and chain extenders. 

MBS (methyl methacrylate-butadiene-styrene) graft copolymers are known as one of the most efficient non-reactive impact modifiers for PET and also poly(vinyl chloride) (PVC). MBS is used commercially as an effective impact modifier for PET recyclate [27], Typical MBS rubber particles contain an elastomeric core of... 

Pecorini and Calvert [28] attribute the role of small particles and a small interparticle distance to inducing high toughness in PET by promoting massive shear yielding in the matrix. Their study showed that the non-reactive impact modifier gives a system in which the rubber phase is not well dispersed. It was shown that this is not effective in toughening PET at levels of either 10 or 20%. The... 

Non-reactive impact modifier (copolymer of ethylene and methyl acrylate). b Reactive impact modifier (terpolymer of ethylene, methyl acrylate and glycidyl methacrylate). c Interparticle distance, i.e. the average distance between particles of impact modifier in the PET matrix. 

Non-reactive impact modifier (copolymer of ethylene and methyl acrylate). 

Reactive impact modifier (teipolymer of ethylene, methyl acrylate and glycidyl methaciylate). 

Super-tough impact strength may be required for apphcations that should not lead to a failure of the part even if hit at low temperatures (—30 to — 40°C) under high speed. This requirement can only be fulfilled with high levels (20—25%) of reactive impact modifier with a low glass transition temperature. 

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