Impact-resistant materials polystyrene

If samples are transported frozen, the packaging containers should be made of a hard and impact-resistant material such as polystyrene. Cardboard cartons with insulating material can also be used. 

Addition of rubbery materials, however, does improve the impact resistance of polystyrene. This is therefore done extensively. The most common rubbers used for this purpose are butadiene-styrene copolymers. Some butadiene homopolymers are also used, but to a lesser extent. The high-impact polystyrene is presently prepared by dissolving the rubber in a styrene monomer and then polymerizing the styrene. This polymerization is either done in bulk or in suspension. The product contains styrene-butadiene rubber, styrene homopolymer, and a considerable portion of styrene-graft copolymer that forms when polystyrene radicals attack the rubber molecules. The product has very enhanced impact resistance. 

Styrene—acrylonitrile (SAN) copolymers [9003-54-7] have superior properties to polystyrene in the areas of toughness, rigidity, and chemical and thermal resistance (2), and, consequendy, many commercial appHcations for them have developed. These optically clear materials containing between 15 and 35% AN can be readily processed by extmsion and injection mol ding, but they lack real impact resistance. 

Impact polystyrene (IPS) is one of a class of materials that contains mbber grafted with polystyrene. This composition is usually produced by polymerizing styrene (by mass or solution free-radical polymerization) in the presence of a small amount (ca 5%) of dissolved elastomer. Some of the important producers of impact-resistant polystyrenes are BASE (Polystyrol), Dow (Styron), and Monsanto (Lustrex). The 1988 U.S. production of impact polystyrene was more than 1 million t (92). 

One of the most important outcomes of these efforts was impact-resistant polystyrene, which was obtained by modifying the brittle material with rubber. The first products were blends of polystyrene and synthetic rubbers recourse was soon made, however, to a principle that Ostromislensky (29) had suggested as early as 1927 styrene monomer was polymerized in the presence of rubber dissolved in it. 

Based on castor oil derived elastomers and crosslinked polystyrene, a simultaneous mode of polymerization can be successfully employed to synthesize prototype engineering materials such as tough, impact resistant plastics and reinforced elastomers. 

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... 

ISO 2897-1 1997 Plastics - Impact-resistant polystyrene (PS-I) moulding and extrusion materials - Part 1 Designation system and basis for specifications ISO 2897-2 2003 Plastics - Impact-resistant polystyrene (PS-I) moulding and extrusion materials - Part 2 Preparation of test specimens and determination of properties ISO 14631 1999 Extruded sheets of impact-modified polystyrene (PS-I) - Requirements and test methods... 

Thanks to their multiphase constitution, block copolymers have the originality to add advantageously the properties of their constitutive sequences. These very attractive materials can display novel properties for new technological applications. In this respect, thermoplastic elastomers are demonstrated examples (l, 2, 3) they are currently used without any modification as elastic bands, stair treads, solings in the footwear industry, impact resistance or flexibility improvers for polystyrene, polypropylene and polyethylene whereas significant developments as adhesives and adherends are to be noted (5.). 

The polymers described above have been chemically pure, although physically helerodisperse. It is oflen possible lo combine two or more of these monomers in the same molecule to form a copolymer. This process produces still further modification of molecular properties and, in turn, modification of the physical properties of file product. Many commercial polymers are copolymers because of the blending of properties achieved in this way. For example, one of the important new polymers of the past ten years has been the family of copolymers of acrylonitrile, butadiene and styrene, commonly called ABS resins. The production of these materials has grown rapidly in a short period of time because of their combination of dimensional stability and high impact resistance. These properties are related to the impact resistance of acrylonitrile-butadiene rubber and the dimensional stability of polystyrene, which are joined in the same molecule. 

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. 

Tn the last decades many attempts have been made to obtain attractive - materials by intimate mixing of two polymers with opposite or complementary properties. For example, the impact resistance of brittle polystyrene is increased by mixing with a rubber the wettability of polyacrylonitrile fiber is increased by mixing with hydrophilic saponified cellulose acetate, and the inconvenient flat-spotting of nylon-reinforced tires is suppressed by mixing stiffer polyester fibrils into the nylon fibers. In practically all cases these products acquire their final shape via the liquid state. Thus, the viscous properties of these liquid mixtures are important. 

PVC can be blended with numerous other polymers to give it better processability and impact resistance. For the manufacture of food contact materials the following polymerizates and/or polymer mixtures from polymers manufactured from the above mentioned starting materials can be used Chlorinated polyolefins blends of styrene and graft copolymers and mixtures of polystyrene with polymerisate blends butadiene-acrylonitrile-copolymer blends (hard rubber) blends of ethylene and propylene, butylene, vinyl ester, and unsaturated aliphatic acids as well as salts and esters plasticizerfrec blends of methacrylic acid esters and acrylic acid esters with monofunctional saturated alcohols (Ci-C18) as well as blends of the esters of methacrylic acid butadiene and styrene as well as polymer blends of acrylic acid butyl ester and vinylpyrrolidone polyurethane manufactured from 1,6-hexamethylene diisocyanate, 1.4-butandiol and aliphatic polyesters from adipic acid and glycols. 

The uniqueness of these polymers is derived from a combination of performance attributes. The SBC family of polymers offers outstanding clarity and excellent impact strength or shatter resistance, and are easy to process. Primarily, these type polymers fill the gap between low-cost commodity materials and high-cost performance polymers. For example, crystal polystyrene offers excellent clarity, but very poor impact resistance, and polycarbonate offers excellent impact resistance, but at a significant cost premium. 

Oriented polystyrene (OPS) is widely used for many packaging applications, including deli and bakery packaging. The biaxial orientation of the crystal polystyrene provides a significant improvement in impact strength and makes a very rigid material. Even with the enhancement of impact resistance, usually some level of impact modifier is required. SBCs are an excellent modifier for OPS. They help maintain the excellent clarity while also improving impact and processability of the OPS. 

Since this paper will be restricted to sequential IPN s based on cross-poly butadiene-inter-cross-polystyrene. PB/PS, it is valuable to examine the range of possible compositions, see Figure 2 ( ). The PB/PS IPN polymer pair models high-impact polystyrene, and in fact, many of the combinations made are actually more impact resistant than the commercial materials. In general, with the addition of crosslinks, especially in network I, the phase domains become smaller. The impact resistance of high-impact polystyrene, upper left, is about 80 J/ra. In the same experiment, the semi-I IPN, middle left is about 160 J/m, and the full IPN, lower left, is about 265 J/m (g). Since the commercial material had perhaps dozens of man-years of development, and the IPN composition was made simply for doctoral research with substantially no optimization, it was obvious that these materials warranted further study. 

A number of polymerization techniques are used in the transformation of monomers into plastics (Chapter 10). These include bulk, solution, suspension, and emulsion polymerization processes. Each of these polymerization techniques has its advantages and disadvantages and may be more appropriate for the production of certain types of polymer materials. For example, bulk polymerization is ideally suited for making pure polymer products, as in the manufacture of optical-grade poly(methyl methacrylate) or impact-resistant polystyrene, because of rninimal contamination of the product. On the other hand, solution polymerization finds ready application when the end use of the polymer requires a solution, as in certain adhesives and coating processes. 

High impact polystyrene (HIPS) is an opaque material that has added butadiene rubber, partially as a blend and partially as a graft copolymer, to improve impact resistance. 

Weather-resistant AXS polymers contain, in place of the UV-labile polybutadi-ene, a low-diene acryloic ester elastomer that is highly weather-resistant. Even polystyrene elastified with low-diene EPDM remains impact-resistant in outdoor applications. Transparent, high-impact polystyrene (SB) is obtained by embedding the - normally opacifying - rubber components in the form of ultrafine lamellae into the coherent PS phase instead of in bead-form particles. The transparency results from the equivalent refractive index of the materials. 

Styrene-acrylonitrile copolymers are produced commercially for use as structural plastics. The typical acrylonitrile content in such resins is between 20-30%. These materials have better solvent and oil resistance than polystyrene and a higher softening point. In addition, they exhibit better resistance to cracking and crazing and an enhanced impact strength. Although the acrylonitrile copolymers have enhanced properties over polystyrene, they are still inadequate for many applications. Acrylonitrile-butadiene-styrene polymers, known as ABS resins, were therefore developed. 

While the impact resistance of the mechanical blends is clearly superior to that of the parent polystyrene, they have two important deficiencies that cause them to be inefficient. First, due to the high viscosity of the melts, the problem of attaining intimate mixing cannot be entirely overcome. As a result, the dispersed phase maintains a relatively large particle size, as shown in Figure 3.1. Second, the two phases are bonded together only by weak van der Waals forces, so that the material as a whole exhibits poor cohesion. 

---