Polystyrene impact strength

DMPPO—polystyrene blends, because of the inherent flame resistance of the DMPPO component (oxygen index ca 29.5), can be made flame retardant without the use of halogenated additives that tend to lower impact strength and melt stabiUty in other polymers. Approximately one-half of total Noryl sales volume is in flame-retarded grades, ie, VO or VI in a 1.6-mm section (UL-94). 

Polystyrene. Polystyrene [9003-53-6] is a thermoplastic prepared by the polymerization of styrene, primarily the suspension or bulk processes. Polystyrene is a linear polymer that is atactic, amorphous, inert to acids and alkahes, but attacked by aromatic solvents and chlorinated hydrocarbons such as dry cleaning fluids. It is clear but yellows and crazes on outdoor exposure when attacked by uv light. It is britde and does not accept plasticizers, though mbber can be compounded with it to raise the impact strength, ie, high impact polystyrene (HIPS). Its principal use in building products is as a foamed plastic (see Eoamed plastics). The foams are used for interior trim, door and window frames, cabinetry, and, in the low density expanded form, for insulation (see Styrene plastics). 

HIPS = high impact strength polystyrene, a graft copolymer and blend with polybutadiene. 

In these mbber-modified polystyrene polymers, the mbbers should have low T, large particle sizes (0.5—5 J.m), graftable and cross-linkable sites, and should be compatible with styrene monomer (93). Polybutadiene, with a T of —SS C, meets all of these requirements and is used most frequently. These mbber-modified systems exhibit excellent low temperature impact strength, a required attribute for use in refrigerators. 

Today the common practice is first to dissolve the rubber in the styrene monomer and then to polymerise the styrene in the usual way. By this process the resultant blend will contain not only rubber and polystyrene but also a graft polymer where short styrene side chains have been attached to the rubber molecules. This gives a marked improvement in the impact strengths that can be obtained. 

A high-impact polystyrene (polystyrene SBR blend) may have seven times the impact strength of ordinary polystyrene, but about half the tensile strength, a lower hardness and a softening point some 15°C lower. Because of the rubber content there may be a reduction in light and heat stability and stabilisers are normally incorporated. 

Figure 16.12. Effect of adding SBR on the impact strength of polystyrene...

More recently Fina Chemicals have introduced linear SBS materials (Finaclear) in which the butadiene is present both in block form and in a mixed butadiene-styrene block. Thus comparing typical materials with a total styrene content of about 75% by weight, the amount of rubbery segment in the total molecule is somewhat higher. As a result it is claimed that when blended with polystyrene the linear block copolymers give polymers with a higher impact strength but without loss of clarity. 

Tough transparent sheet may be produced by blending standard polystyrene with block copolymer in an extruder in the ratios 80 20 to 20 80, depending on the application of the products subsequently thermoformed from the sheet. For example, sheet for thermoforming an egg tray will not require the same level of impact strength as that required for jam jars. 

The brittleness of isotactic polystyrenes has hindered their commercial development. Quoted Izod impact strengths are only 20% that of conventional amorphous polymer. Impact strength double that of the amorphous material has, however, been claimed when isotactic polymer is blended with a synthetic rubber or a polyolefin. 

It may be prepared in two stereo-regular forms, cis- and trans-. The cii-polymer, which crystallises in zig-zag form, has a of 235°C, whilst the fran -polymer, which crystallises in helical form, melts at the much lower temperature of 145°C. Tensile strengths of both forms are reportedly similar to that of Penton whilst the tensile modulus of 2300 MPa is about twice as high. Unfortunately the material is rather brittle with an impact strength only about half that of polystyrene although this may be improved by orientation. 

Polystyrene (PS). Polystyrene is available in a range of grades which generally vary in impact strength from brittle to very tough. The non-pigmented... 

Methylpentene polymer, a light plastic, has a crystalline melting point of 464 retention up to 392° F, transparency of 92%, and electrical properties similar to fluoroethylene. Its impact strength is greater than polystyrene and polymethyl methacr resistant to alkalies, weak acids, and non-chlorinated solvents. It may be injection m< implements for food packaging and preparation, medical care, and non-stick coating ... 

The formation of the polyalloy results in improvement in the performance of the blends. This system is similar to the production of high-impact polystyrene (HIPS) where a rubber is dissolved in styrene monomer and then polymerized in the usual way. Even though the impact strength of the compatibilized PS-PE blend was higher than that of PS, it was much less than that of HIPS. In another study. Van Ballegooie and [55] have confirmed... 

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. 

Hong, B. K. and Jo, W. H. (2000) Effects of molecular weight of SEBS triblock copolymer on the morphology, impact strength, and rheological property of syndiotactic polystyrene/ ethylene-propylene rubber blends. Polymer, 41, 2069-2079. 

Polystyrene is brittle. Rubber (5-15%) is added to improve this property. This is known as impact polystyrene. It is obtained by polymerising styrene in the presence a rubber. This impact polystyrene is having reduced clarity, softening point and tensile strength but better impact strength. 

The copolymer is having a higher softening point and improved impact strength than the linear polystyrene. Due to the polar nature of acrylonitrile, the copolymers are some what more resistant to hydrocarbons and oils than polystyrene. 

The SIN s from castor oil and the other oils were tough materials, either reinforced elastomers or impact resistant plastics depending on their composition and whether phase inversion had occurred. Impact strengths in the range of 40-60 J/m were obtained. The glass transitions of the rubber phase of the SIN s tended to be a little higher than those shown in Table IV. The polystyrene phase... 

Figure 4.40 shows an example of impact strength versus low temperatures for a given impact-modified polystyrene. 

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

The addition of 20% Ecoflex in PLA reduces the stiffness of PLA by 25% (Fig. 6), keeping the impact strength (e.g., Charpy unnotched impact strength at —20°C, according to ISO 179/leU) at 22 kJ/m, which is above the level of high impact polystyrene. Containers produced from this compound are resistant even to sudden strokes and deform without brittle failure at room temperature (23°C). 

Polycarbonate is blended with a number of polymers including PET, PBT, acrylonitrile-butadiene-styrene terpolymer (ABS) rubber, and styrene-maleic anhydride (SMA) copolymer. The blends have lower costs compared to polycarbonate and, in addition, show some property improvement. PET and PBT impart better chemical resistance and processability, ABS imparts improved processability, and SMA imparts better retention of properties on aging at high temperature. Poly(phenylene oxide) blended with high-impact polystyrene (HIPS) (polybutadiene-gra/f-polystyrene) has improved toughness and processability. The impact strength of polyamides is improved by blending with an ethylene copolymer or ABS rubber. 

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