Engineering Plastics 7 Polyacetal

Polymers that are rigid at high temperatures are known as engineering plastics . This class of polymers includes polyacetal and many nylons. These polymers are used in applications such as small gears in office equipment and under the hood of automobiles. 

As can be deduced from plant purchases, the PRC is still at the formative stage where emphasis is on producing only the most basic petrochemicals. No plants were purchased for producing dibasic acids (phthalic and maleic anhydrides, etc.) and fluro-carbon or tetrafluoro ethylene or some of the advanced engineering plastics like ABS polyacetals, polycarbonates, polyimides or any other unsaturated polyesters. Another important area of low Chinese activity is thermoplastics for space and defense applications. ... 

Polyacetals and other engineering plastics cost about half that of cast metals, and are therefore used as replacements for cast metal-intense applications. They have been approved by the Food and Drug Administration for contact with foods. Some of the uses of molded polyacetals are as valves, faucets, bearings, appliance parts, springs, automotive window brackets, hose clamps, hinges, video cassettes, tea kettles, chains, flush toilet float arms, gears, shower heads, pipe fittings, pasta machines, desktop staplers, and air gun parts. 

Trioxane copolymers (often called polyacetals) are used as engineering plastics in automotive, machinery, and electric industry. 

Nylon, polyacetal, polycarbonates, poly(2,6-dimethyl)phenylene oxide (PPO), polyimides, polyphenylene sulfide (PPS), polyphenylene sulfones, polyaryl sulfones, polyalkylene phthalates, and polyarylether ketones (PEEK) are stiff high-melting polymers which are classified as engineering plastics. The formulas for the repeating units of some of these engineering plastics are shown in Figure 1.15. 

Cationic polymerization of 1,3,5-trioxane provides one of a few examples of industrial application of cationic ring-opening polymerization. Polymerization leads to polyoxymethylene (polyformaldehyde, polyacetal), important engineering plastic. Polyformaldehyde may also be obtained by anionic polymerization of formaldehyde and this process is also used in industry. 

Fortunately, the deficiencies of both the classic thermosets and general purpose thermoplastics have been overcome by the commercialization of a series of engineering plastics including polyacetals, polyamides, polycarbonate, polyphenylene oxide, polyaryl esters, polyaryl sulfones, polyphenylene sulfide, polyether ether ketones and polylmides. Many improvements in performance and processing of these new polymers may be anticipated through copolymerization, blending and the use of reinforcements. 

The most stable polyacetal polymer is polyformaldehyde (or polyoxymeth-ylene, POM) this is the only polyacetal that has reached commercial production. This resin has unique properties (e.g., selflubrication) and is very widely used in automotive applications such as engineering plastics. Acetals are widely used engineering thermoplastics with high load-bearing characteristics and low coefficients of friction. Currently, over 200 million lb of acetals are molded and extruded in the United States. 

Though useful polymers can be made by these reactions, their low ceiling temperatures (see p. 599) and consequent tendency to undergo facile depolymerization by an unzipping mechanism pose serious limitations. To overcome this problem the technique of end-capping or end-blocking may be used. Thus poly-oxymethylene (polyacetal), an engineering plastic, prepared from the cyclic acetal... 

Polyacetal polyphenylene oxide are widely used as engineering thermoplastics, and epoxy resins are used in adhesive and casting application. The main uses of poly(ethylene oxide) and poly(propylene oxide) are as macroglycols in the production of polyurethanes. Polysulfone is one of the high-temperature-resistant engineering plastics. 

Polyacetals are engineering plastics because of their high hardness, rigidity and tensile strength, good abrasion and wear resistance, and favorable low frictional properties, all of which are advantages over other materials. Since polyacetals absorb virtually no water, they have excellent weight retention characteristics. Polyacetals only dissolve in hexafluoroacetone hydrate at... 

Traditionally, material design requirements that suit such demanding end-use applications have been limited within the domain of engineering plastics based on polyamide 6 or 66, polyester alloys, and polyacetal type resins. However, as described in Chapter 1, glass fiber-reinforced polypropylene (GFRP) composites continue to gain a market share in automotive molded parts. 

Zsidai and co-workers [29] reported results of a series of test carried out to determine the friction properties of engineering plastics by the measurement of small and large test specimens on a steel and diamond-like carbon coating surface. The objective was to compare the friction properties of a surface provided with a diamond-like carbon coating with measurements obtained on a steel surface as a function of the engineering plastic used, and to examine the practical possibilities of the diamond-like coating. The plastics tested included PA, polyacetals and PET/PTFE. 

Custom compounders Ashley Polymers Polyacetals, other engineering plastics... 

Polyacetals DuPont (150) Polyplastics (150) Ticona (150) Ultraform (70) Korea Engineering Plastics (55) Asahi Kasei (44) Mitsubishi Engineering (20) Thai Polyacetal (20) Zaklady Azotowe Tamowie (10) 2920-3490... 

In principle, engineering plastics and high performance polymers are affected by these trends in the same way, as the margin development for polyesters and polyacetal shows (see Figure 1.10.)... 

Margolis JM. Polyacetals. In MargoUs J, editor. Engineering plastics handbook thermoplastics, properties, and applications. New York McGraw-Hill 2006. p. 77-100. Chapter 5. 

In the following data acquisition, the same 163 standard polymer samples used in the former edition were adopted as a set of representative ones utilized in versatile fields, which include representative synthetic polymers [a) polyolefins (homopolymers) (001— 007), b) vinyl polymers with ethylene units (copolymers) (008—015), c) vinyl polymers with styrene units (016—028), d) vinyl polymers with styrene derivatives (029—035), e) acrylate-type polymers (036—049), f) chlorine-containing vinyl polymers (050-059), g) fluorine-containing vinyl polymen (060—066), h) the other vinyl polymers (067—070), i) diene-type elastomers (071—081), j) polyamides (082-090), k) polyacetals and polyethers (091—095), 1) thermosetting polymers (096—106), m) polyimides and polyamide-type engineering plastics (107—114), n) polyesters (115—126), o) the other engineering plastics with phenylene skeletons (127—138), p) sificone polymers (139—143), and q) polyurethanes (144—147)] along with some natural polymers [r) cellulose-type polymers (148-155) and s) the other some natural polymers (156-163)]. 

PES and PSU were first commercialised by BASF in 1965. They are semi-transparent, very high temperature resistant amorphous thermoplastics that are used where the performance requirements exceed the capabilities of other engineering plastics such as polyamide, PBT and polyacetals. PES and PSU can also replace thermosets, metals and ceramics. 

The most widely used engineering plastic is ABS with total world consumption of 4,667,000 tonnes in 2002. Polyamide is the second largest category with total consumption of 1,950,000 tonnes, followed by polycarbonate with 1,714,000 tonnes. Acrylics, polyacetal and PBT are also well-established and high volume engineering plastics. 

The world polyacetal market is highly concentrated in the hands of a few global businesses. Ticona GmbH claims around a 45% share of the global market, including its Polyplastics joint venture with Daicel Chemical Industries. DuPont is the world s number two supplier, followed by the BASF/Degussa joint venture Ultraform, and then by smaller Asian players such as Asahi Chemical and Mitsubishi Engineering Plastics. 

Ticona GmbH, is the engineering plastics subsidiary of Celanese AG, and the leading worldwide POM supplier with total capacity of 165,000 in 2002. The main production sites for acetals are located in Bishop, Texas, and Kelsterbach, Germany. Ticona increased production capacity for polyacetal resins at the Kelsterbach plant, from 77,000 tpa to 100,000 tpa at the end of 2002. 

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