Injection moulding polystyrene

Extractability tests were carried out on injection moulded polystyrene cups with a nominal wall thickness of 0.02 inch containing 1.5% lauric diethanolamide as an antistatic additive. Tests were run for 10 days at 60 °C and total undegraded plus degraded lauric diethanolamide (i.e., DEA) was determined in each extractant and calculated as grams lauric diethanolamide extracted per 4000 cm of plastic surface. 

Table 13.11 Extractability of lauric diethanolamide from injection moulded polystyrene cups containing 1.5% DEA...

Sandllands, G.J. and White, J.R., Effect of Injection Pressure and Crazing on Internal Stresses in Injection Moulded Polystyrene. Polymer 21 338-343 (1980). 

Whilst it is inevitable that polypropylene will be compared more frequently with polyethylene than with any other polymer its use as an injection moulding material also necessitates comparison with polystyrene and related products, cellulose acetate and cellulose acetate-butyrate, each of which has a similar rigidity. When comparisons are made it is also necessary to distinguish between conventional homopolymers and the block copolymers. A somewhat crude comparison between these different polymers is attempted in Table 11.7 but further details should be sought out from the appropriate chapters dealing with the other materials. 

In 1930 BASF, then part of IG Farhen, installed a plant for producing 100 tonnes of polystyrene per annum and in 1933 the first injection moulded articles were produced. In the US semi-plant-scale work at the Dow Chemical Company showed promise of commercial success in 1934. As a consequence there became available shortly before World War II a material of particular interest because of its good electrical insulation characteristics hut otherwise considerably inferior to the polystyrene available today. Because of these excellent electrical characteristics prices were paid of the order of several dollars per pound for these polymers. 

Polystyrene and closely related thermoplasties such as the ABS polymers may be proeessed by sueh techniques as injection moulding, extrusion and blow moulding. Of less importance is the processing in latex and solution form and the... 

The negligible water absorption avoids the need for predrying granules. The low specific heat (compared with polyethylene) enables the polymer to be rapidly heated in injection cylinders, which therefore have a higher plasticising capacity with polystyrene than with polyethylene. The setting-up rates in the injection moulds are also faster than with the polyolefins so that faster cycles are also possible. 

Although it is not difficult to make injection mouldings from polystyrene which appear to be satisfactory on visual examination it is another matter to produce mouldings free from internal stresses. This problem is common to injection mouldings of all polymers but is particularly serious with such rigid amorphous thermoplastics as polystyrene. 

One alternative approach to the two-stage steam moulding process is that in which impregnated beads are fed directly to an injection moulding machine or extruder so that expansion and consolidation occur simultaneously. This approach has been used to produce expanded polystyrene sheet and paper by a tubular process reminiscent of that used with polyethylene. Bubble nucleating... 

Tbe term structural foam was originally coined by Union Carbide to describe an injection moulded thermoplastic cellular material with a core of relatively low density and a high-density skin. The term has also been used to describe rigid foams that are load bearing. Today it is commonly taken to imply both of the above requirements, i.e. it should be load bearing and with a core of lower density than the skin. In this section the broader load-bearing definition will be used. Whilst structural foams are frequently made from polymers other than polystyrene, this polymer is strongly associated with such products and it is convenient to deal with the topic here. 

In recent years general purpose polystyrene and high-impact polystyrenes have had to face intensive competition from other materials, particularly polypropylene, which has been available in recent years at what may best be described as an abnormally low price. Whilst polystyrene has lost some of it markets it has generally enjoyed increasing consumption and the more pessimistic predictions of a decline have as yet failed to materialise. Today about 75% of these materials are injection moulded whilst the rest is extruded and/or thermoformed. 

The largest outlet for polystyrene is in packaging applications. Specific uses include bottle caps, small jars and other injection moulded containers, blown containers (a somewhat recent development but which has found rapid acceptance for talcum powder), vacuum formed toughened polystyrene as liners for boxed goods and oriented polystyrene film for foodstuffs such as creamed... 

The processing of blends of an amorphous material (polystyrene) and a crystalline material with a high melting point (PPO) reflects the nature of the constituent materials. The processing is mainly by injection moulding, and the major points to be considered when processing Noryl-type materials are ... 

Isometric data from the creep curves may also be superimposed on the creep rupture data in order to give an indication of the magnitudes of the strains involved. Most plastics behave in a ductile manner under the action of a steady load. The most notable exceptions are polystyrene, injection moulding grade acrylic and glass-filled nylon. However, even those materials which are ductile at short times tend to become embrittled at long times. This can cause... 

An important aspect of this enhancement strategy is its compatibility with current fabrication techniques, in particular polymer processing technology. The technique of micro-injection moulding was employed to produce polystyrene chips with an integrated array of cone structures intended for use in an aqueous environment. 

The dithiocarbamates have the pentacoordinate binuclear structure (44). The diamyl- and diethyl-dithiocarbamate complexes have been found to inhibit the hardening of asphalt, but the effect appears too weak to be useful.127 The latter complex is an effective antioxidant for polyethylene,128 polypropylene,129 polystyrene,130 poly(methyl methacrylate)130 and an isoprene-styrene copolymer.131 The di-n-butyldithiocarbamate complex is important in the vulcanization and injection moulding of rubber,132 as a stabilizer against photolytic and thermal degradation. 

Polystyrene is an inexpensive transparent plastic which is often used in industry for the fabrication of parts by injection moulding. However, the tougher acrylic plastics are preferable for the construction of laboratory apparatus. Polystyrene is soluble in many organic liquids and, if strain free, may be solvent-bonded by the use of chlorinated hydrocarbons, benzene, or toluene. Special impact-resistant grades are available which are less susceptible to solvents and thus a little harder to solvent-bond than the conventional material. Polystyrene also may be welded. 

PLA is a polymer that may not be well suited to injection moulding. Its rate of crystallisation is too slow to allow cycle times typical of those for commodity thermoplastics such as polystyrene. Stress induced crystallisation that can enhance PLA crystallisation is better suited to processes such as fibre spinning or biaxial orientation of film. 

FKuR also introduced Biograde 200C in 2005, an unfilled cellulose blend with high stiffness and transparency for cast film and injection moulding. The material can also be blow moulded into bottles and thermoformed into cups and trays. Injection moulded Biograde 200C exhibits properties comparable to polystyrene, but with the addition of barrier performance comparable to PLA. It consists of 100% renewable resources, but does not contain starch. 

Bomatic, Inc. has been a producer of plastic bottles and containers since 1969. The company serves the personal care, automotive, pharmaceutical, medical, lawn and garden, food, household cleaners, and industrial chemicals markets. Production capabilities include extrusion blow moulding and injection moulding products made from HDPE, PVC, LDPE, PET, PETG, polycarbonate, polystyrene, polypropylene, and polyurethane. 

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