Toughness polyacetals

From the time that formaldehyde was first isolated by Butlerov in 1859 polymeric forms have been encountered by those handling the material. Nevertheless it is only since the late 1950s that polymers have been available with the requisite stability and toughness to make them useful plastics. In this period these materials (referred to by the manufacturers as acetal resins or polyacetals) have achieved rapid acceptance as engineering materials competitive not only with the nylons but also with metals and ceramics. 

Blends or alloys of polyacetals with polyurethane elastomers were first introduced by Hoechst in 1982, who were then followed by other manufacturers. The key features of these materials are their improved toughness with little change in other important properties. There are two aspects with respect to the impact toughness ... 

POMlElastomer (Polyacetal or Polyoxymethylene). It has toughness, good notched Izod resistance, and chemical resistance. It is used in interior automotive, gears, cams, etc. 

One of the attractions of the fracture mechanics approach is that the results are geometry independent. This, of course, is subject to conducting tests with valid specimens that meet the dimensions criteria set out in the standards. Considerable work has been conducted with various materials to verify how appropriate these specimen size criteria are for specific polymers and to a.scertain how sensitive the test results are to changes in specimen dimensions and to deviations from the criteria. The specimen thickness is the geometric variable that is considered most, since it governs whether the fracture is plane-strain or not. The effect of specimen thickne.ss B on fracture parameters, e g., K, G, J. and CTOD. has been examined for uPVC [23.61], polycarbonate [23,63], HIPS [64], HOPE [37,59,60,], ABS [65], and ABS PC blends [74], The effect of a/IF on fracture toughness properties is also considered for some of these materials, e g, uPVC [25], HOPE [59.60], polyacetal [68], and polyether sulphone (PES) [70]. 

Plastics have been widely accepted in industrial equipment development as materials for many critical components and for accessories where such features as toughness, abrasion resistance, corrosion resistance, electrical insulation capability, nonstick properties, and transparency are of importance. For example, PVC, polyacetal, and PTFE are used for pipes, pumps, and valves because of their excellent corrosion resistance. Nylons are used for such diverse applications as mine conveyor belts and main drive gears for knitting machines and paper making equipment because of their excellent abrasion resistance, toughness, and low coefficient of friction. 

Beg Beguelin, P., Kausch, H.-H. The effect of the loading rate on the fracture toughness of poly (methyl methacrylate), polyacetal, polyetheretherketone and modified PVC. J. Mater. Sci. 29 (1994) 91-98. 

Linear, hard, tough synthetic resins produced by the polymerisation of formaldehyde (for acetal homopolymers) or of formaldehyde with trioxane (for acetal copolymers). Acetal resins are also called as polyacetals and are used as substitutes for metals. 

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