Toughening effect polyamide

Table 3.9 Examples of toughening effects on properties of polyamide and polyacetal...

Shape memory effect of polylaclide/polyamide elastomer (PLA/PAE) (90/10 wt/wt) blends. (The sample can recover to original shape in 8 s and 3 s at 80 and 90°C, respectively.) (Adapted from Zhang, W., Chen, L., and Zhang, Y. 2009. Surprising shape-memory effect of polylactide resulted from toughening by polyamide elastomer. Polymer 50 1311-1315. Copyright Elsevier Ltd. Reproduced with permission)... 

Zhang, W., Chen, L., and Zhang, Y 2009. Surprising shape-memory effect of poly-lactide resulted from toughening by polyamide elastomer. Polymer 50 1311-1315. 

Wahit, M. U., Hassan, A., Mohd Ishak, Z. A., and Czigdny, T. 2009. Ethylene-octene copolymer (POE) toughened polyamide 6/polypropylene nanocomposites Effect of POE maleation. e-EXPRESS Polymer Letters 3 309-319. 

Polyamide 6 can be toughened more effectively by blending it with maleated MABS (methacrylate-acrylonitrile-butadiene-styrene copolymer) than with ordinary MABS. 

Polyamides and saturated polyesters can be toughened with ABS, ethylene-propylene copolymers/terpolymers or EPDM rubbers grafted with maleic anhydride to increase the dispersion and adhesion of the modifier. Styrene-butadiene copolymers are also effective. The notched Izod impact strength of polyamide 6-6 can be increased more than 20-fold by impact modifiers, whereas short glass fibres often reduce the impact strength, even though they increase the modulus. 

DuPont s Fusabond AEB-560D is a modified ethylene-acrylate copolymer for use in polyamides. It is claimed to be a cost-effective toughener, more effective than maleic anhydride terpolymers and usable at low temperatures, while improving mould flow, with less of an adverse effect on the flexural modulus. 

Modification of commercial polymers to enhance their toughness has become a major new field of polymer science. The commercial success of HIPS and ABS led to the development of a whole new group of mbber-toughened plastics (1-3). Chapter 1 provides trend data for the use of polypropylene (PP) resins as cost-effective replacement of engineering polymers. With the development of tailored polypropylene copolymers (see Chap. 2) and plastomers for impact modification (see Chap. 7), composites of fillers and fibrous reinforcement can be effectively toughened to compete with polyamide type products. 

The effect of polymer blend morphology on the stiffness and toughness of blends of ethylene-co-propylene rubber (EPR) in polyamides (PA) has been the subject of a number of recent papers and patents (1-7). In these toughened blends, the rubber exists as a separate phase of discrete particles. It has been shown that both the rubber particles size and total volume fraction have an effect on toughness and, especially, the ductile-to-brittle transition temperature (DBTT). 

In other cases it is not sufficient to have physical interactions, but it is necessary to create chemical bonds with the matrix to achieve effective toughening. This is the case with polyamides, and blends of PA with PPO. To this purpose reactive sites must be present on the outer shell of the grafted rubber particles, giving rise to in situ reactions of the kind illustrated above. 

Kelnar J, Kotek J, Kapralkovtl L, Hromddkovd J and Kratochvfl J (2006) Effect of elastomer type and functionality on the behavior of toughened polyamide nanoconipos-ites, J Appl Polym Sci 100 1571-1576. 

Crucial to the high toughening efficiency of the maleated rubbers is the reaction between the bound anhydride functionality and the amine end groups of polyamide (Scheme 8.3) to form the critical graft copolymer at the interface. The graft copolymer effectively compatibilizes the rubber by reducing the interfacial tension according to the currently... 

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