Polystyrene weathering

The important features of rigidity and transparency make the material competitive with polystyrene, cellulose acetate and poly(methyl methacrylate) for a number of applications. In general the copolymer is cheaper than poly(methyl methacrylate) and cellulose acetate, tougher than poly(methyl methacrylate) and polystyrene and superior in chemical and most physical properties to polystyrene and cellulose acetate. It does not have such a high transparency or such food weathering properties as poly(methyl methacrylate). As a result of these considerations the styrene-acrylonitrile copolymers have found applications for dials, knobs and covers for domestic appliances, electrical equipment and car equipment, for picnic ware and housewares, and a number of other industrial and domestic applications with requirements somewhat more stringent than can be met by polystyrene. 

Because of their toughness and good appearance ABS polymers have become regarded as a de luxe form of polystyrene, their biggest drawbacks being their limited weathering resistance and relatively high cost. It is one of the few major polymers where there is different pattern of use in North America compared with Europe. 

Where transparency is required, a range of polymers is available. Polystyrene is the least expensive but polymethylmethacrylate has an outstanding high light transmission combined with excellent weathering properties. Also to be considered are the polycarbonates, glass-clear polyamides, SAN, butadiene-styrene block copolymers, MBS polymers, plasticised PVC, ionomers and cellulose esters such as cellulose acetate. 

Weathering in a tropical climate causes polyethylene containers to crack, polypropylene (PP) ropes to rupture, and ABS telephones to foil. Polystyrene (PS) and cellulose acetate films used as packing materials also fail due to weathering. 

Polystyrene One of the high volume plastics, is relatively low in cost, easy to process, has sparkling clarity, and low water absorption. But basic form (crystal PS) is brittle, with low heat and chemical resistance, poor weather resistance. High impact polystyrene is made with butadiene modifiers provides significant improvements in impact strength and elongation over crystal polystyrene, accompanied by a loss of transparency and little other property improvement. PS is used in many different formulations. 

Titus, Weatherability of Polystyrenes and Related Copolymers and Terpolvmers . PLASTEC Rept 38 (1969) 32) N.E. Beach, Compati-... 

P.R.48 5, a magnesium salt, was a comparatively recent product but its manufacture has already been discontinued. It is considerably yellower and at the same time more brilliant than P.R.48 4. The pigment is also much weaker in white reductions. Compared to the manganese version, P.R.48 5 does not perform as well if exposed to light and/or weather, and it darkens in full shades. Its primary field of application is the pigmentation of polyolefins, but it is also employed to color PVC and polystyrene. Its application properties and fastness properties in print and in paints largely parallel those of P.R.48 2. 

The first move in this direction was to improve the weatherability of impact-resistant polystyrene. Because polybutadiene, the most widely used rubber in impact-resistant polystyrene, is unsaturated, it is sensitive to photooxidation, and impact-resistant polystyrene is therefore not suitable for outdoor applications. A saturated rubber might be able to help here. In the ABS sector this has been successfully tried out with acrylate rubber (77) and EPDM (78, 79), and the latter has also been used in impact-resistant polystyrene (80, 81) This development has elicited satisfactory responses only in certain areas and more work still has to be done. For instance, attempts have been made to improve resistance to weathering by using silicone rubber (82 ). This approach is effective, but economic factors still stand in its way. Further impetus may also be expected from stabilizer research. Hindered secondary amines (83), to which considerable attention has recently been paid, are a first step in this direction. 

Transparent block copolymers of styrene and butadiene, having polystyrene character (Phillips). Weather-resistant, impact-resistant polystyrene with EPDM rubber (Mitsui Toatsu, Hoechst). 

Figure 4.43. SN curve of polystyrene, examples of maximum stress S (MPa) versus number of cycles at rupture (N) Weathering...

Acrylonitrile improves the gloss, mechanical and chemical performances of polystyrene. Butadiene improves impact strength but alters weathering and optical properties for the alloys. 

More expensive than commodities such as polyolefins, PVC and polystyrene brittle when dry, sensitive to water (swelling up to 10%, decrease in mechanical and electrical properties) opaque or translucent require UV and weathering protection significant shrinkage after moulding inherent flammability (but FR grades are marketed). 

SEES is chosen for a better oxidation, ageing and weathering resistance a broader rigidity range and better retention of properties when the temperatures rise above the glass transition of polystyrene. 

Most polystyrene products are not homopolystyrene since the latter is relatively brittle with low impact and solvent resistance (Secs. 3-14b, 6-la). Various combinations of copolymerization and blending are used to improve the properties of polystyrene [Moore, 1989]. Copolymerization of styrene with 1,3-butadiene imparts sufficient flexibility to yield elastomeric products [styrene-1,3-butadiene rubbers (SBR)]. Most SBR rubbers (trade names Buna, GR-S, Philprene) are about 25% styrene-75% 1,3-butadiene copolymer produced by emulsion polymerization some are produced by anionic polymerization. About 2 billion pounds per year are produced in the United States. SBR is similar to natural rubber in tensile strength, has somewhat better ozone resistance and weatherability but has poorer resilience and greater heat buildup. SBR can be blended with oil (referred to as oil-extended SBR) to lower raw material costs without excessive loss of physical properties. SBR is also blended with other polymers to combine properties. The major use for SBR is in tires. Other uses include belting, hose, molded and extruded goods, flooring, shoe soles, coated fabrics, and electrical insulation. 

In terms of weatherabilityf polystyrene does not exhibit ultraviolet stability and is not considered we ather-re sis tan t as a clear material. Continuous, long-term exposure results in discoloration and reduction of strength. Improvement in weatherability can be obtained by the addition of ultraviolet absorbers, or by incorporating pigments. The best pigmenting results are obtained with finely dispersed carbon black. 

Polypbenylsulfone Polystyrene Polysuifone Excellent thermal stability, resists creep, inherent high color Excellent processibility, poor UV resistance, brittle Excellent thermai/hydrolytic stability, poor weatherability/impact strength... 

Atactic polystyrene (aPS) is clear, transparent and easily fabricated, and has reasonable mechanical and thermal properties but is slightly brittle and softens near 100 °C. It is readily attacked by a large variety of solvents, including dry-cleaning agents. Its stability to outdoor weathering is poor it turns yellow and... 

Li, T. White, J.R. Residual stress distribution modification caused by weathering in polypropylene and polystyrene. Polym. Eng. Sci. 1997, 37, 321-328. 

In the current study, samples of impact polystyrene that contained a combination of light stabilizers LS I and LS II and samples that contained no light stabilizers were weathered outdoors in Florida and were monitored for changes in physical appearance and for changes in the chemical structure of the surface by use of a multiple internal reflectance IR spectrophotometer. Also, samples of a thermoplastic polyurethane that was stabilized with just LS I and samples that contained no light stabilizers were weathered and monitored in the same way as the impact polystyrene. We hope to establish at what point... 

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