Polyoxymethylene blends

Polyoxymethylene polymers, POM, commonly known as polyacetals or Acetal resins are linear thermoplastic polymers containing predominantly the -CH -O- repeat unit in their backbone. There are two types of acetal resins available commercially (1) homopolymers made by the polymerization of formaldehyde, followed by endcapping, (2) copolymers derived from the ring opening polymerization of trioxane (a cyclic trimer of formaldehyde), and a small amount of a comonomer such as ethylene oxide. Acetal resins are 

Typical properties of commercial impact modified POM resins are shown in Table 15.29. With the increase in the impact strength of these blends, there is a corresponding decrease in the modulus, strength and DTUL relative to the neat POM resin. Impact modified POM blends are still low volume in usage relative to unmodified POM. About 80% of the impact modified POMs are used in the automotive area in typical applications such as electrical switches, fuel system components, gears and hardware. Industrial applications include cams, gears, valves, impellers, pumps and a variety of plumbing and appliance parts. 

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Zhang, Q., and Fu, Q. (2009) Shear-induced change of phase morphology and tensile property in injection-molded bars of high-density polyefhylene/polyoxymethylene blends. Ei4T. pdym. J., 45, 747-756. 

Engineering polymers are often used as a replacement for wood and metals. Examples include polyamides (PA), often called nylons, polyesters (saturated and unsaturated), aromatic polycarbonates (PCs), polyoxymethylenes (POMs), polyacrylates, polyphenylene oxide (PPO), styrene copolymers, e.g., styrene/ acrylonitrile (SAN) and acrylonitrile/butadiene/styrene (ABS). Many of these polymers are produced as copolymers or used as blends and are each manufactured worldwide on the 1 million tonne scale. 

The decorative laminates described in the previous chapter are made with selected thermosetting resins while resins of this type can be moulded and extruded by methods similar to those outlined in the present and the next chapter the materials employed for these processes predominantly are thermoplastic. Many such plastics can be moulded and extruded under suitable conditions, the most important in terms of quantities used being those that combine properties satisfactory for the purpose with convenience in pro-cessing-especially the polyolefins (polyethylene and polypropylene), poly(vinyl chloride), and styrene polymers and blends. Other plastics with special qualities, such as better resistance to chemical attack, heat, impact, and wear, also are used—including acetals (polyformaldehyde or polyoxymethylene), polyamides, polycarbonates, thermoplastic polyesters like poly(ethylene terephtha-late) and poly(butylene terephthalate), and modified poly(phenylene oxide),... 

The identification of polymer blends is illustrated by the DTA curve in Figure 7.48. Chiu (154) studied a physical mixture of seven commercial polymers high-pressure polyethylene (HPEE), low-pressure polyethylene (LPPE), polypropylene (PP), polyoxymethylene (POM), Nylon 6, Nylon 66, and polytetrafluoroethylene (PTFE). Each component shows its own characteristic melting endothermic peak, at 108,127,165,174,220,257, and 340°C, respectively. Polytetrafluoroethylene also has a low-temperature crystalline transition at about 20°C. The unique ability of DTA to identify this polymer mixture is exceeded by the fact that only 8 mg of sample was employed in the determination. 

Structures involving the ether linkage are often employed as blend components. The thermal stability of polyoxymethylene, POM, blends with polyurethane have been studied and these were found to have higher activation energies for decomposition than either of the components [Kumar et al., 1993]. The opposite effect occurred in miscible PEG blends with Phenoxy (the polyhydroxy ether of bisphenol-A) although the degradation process was affected by composition, the addition of the Phenoxy had a negative effect on blend stability [Iriarte et al, 1989]. 

TiOj-polyethylene nanocomposites were fabricated via melt blending technique [37,66]. Similarly, TiO -PP nanocomposite was prepared via melt blending technique [67]. ZnO-polyoxymethylene nanocomposites were prepared by melt blending technique [35]. 

Compatibilized blends of hydroxylated polyoxymethylene (polyacetal) with carboxylic acid-functionalized PP have been prepared (Chen et al. 1991). The formadtHi of ester linkages between the polymers was proposed. For example, blends comprising hydroxylated polyoxymethylene and muconic acid-grafted PP were made into film by calendering at 200 °C to provide compositions with markedly improved mechanical properties compared to similar blends containing unfunctionahzed PP or unfunctionalized polyoxymethylene. 

Polyethylene, LDPE, or polypropylene, PP, were blended with 1-10 wt% polyoxymethylene, POM, for improved melt flow properties, processability, and extrudate appearance A. Rudin, H. P. Schreiber, Canadean Patent 688,416 688,578, 09 June 1964, Appl. 18 May 1963, to Canadian Industries Ltd. 

Table 19.31 Properties of some ctnnmercial polyoxymethylene/impact modifier blends ...

Keywords blends, alloys, miscibility, compatibilization, crystallization, nucleation, polyamide (PA-6, PA-66), polycarbonate (PC), thermoplastic polyesters (PET, PBT), polyoxymethylene (POM), pol3 henylene ether (PPE), ethylenevinylacetate (EVA), grafting with maleic anhydride (MA), grafting with glyddyl methacrylate (GMA), liquid crystal pol)oners (LCP), copolymer compatibilizer. 

Polyaramide and Par/PET blends were sold by Amoco with high heat resistance and impact strength. Celanese introduced the polyoxymethylene (POM)/PBT and POM/thermoplastic urethane (TPU) blends. Polyphenylene ether polyamide blends (PPE)/PA blends were prepared by GE Plastics with good solvent and heat resistance. 

The blends described in the EDCPB provide a cross section of commercial alloys available in Asia, Europe, and North America. The focus is on blends with the five principal engineering resins polyamides, thermoplastic polyesters, polycarbonates, polyoxymethylenes (acetals), and polyphenylene ethers. There are but few examples of the commodity (and these mainly with polypropylene) as well as with high performance specialty resin blends. This may leave a wrong impression of the global blend industry. 

K. Pielichowski and A. Leszczyfiska, TG-FTIR study of the thermal degradation of polyoxymethylene (POM)/thermoplastic polyurethane (TPU) blends. Journal of Thermal Analysis and Calorimetry, 78 (2004), 631-7. 

DMTA together with other techniques such as DSC have been used in morphological studies on a variety of polymers including epoxy-polyaniline resin [53], ethylene-propylene 5-ethylidene-2-norbornene terpolymer-polyaniline blends [54], Nylon 6-ethylene vinyl alcohol blends [55], polyoxymethylene [56], ethylene-propylene-... 

These have often been modified by addition of PE. Blends with polyoxymethylene showed complex anomalous behavior due to interfacial phenomena [34]. PE appeared useful as a melt flow promoter in polyphenylene ether [19]. Dispersion of PE in polycarbonate improves melt flow and energy absorption for automotive applications [19], so PC producers offer such grades commercially [35] fine stable polyethylene domains may be produced by adding PE-PS or SEBS block copolymers [36,37]. 

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