Plastic brittle

The Rheo-Tex rheometer is an inexpensive, automated instmment using load cell technology to measure indentation and creep. Available software calculates hardness/softness, brittleness, plasticity, and tensile strength. This instmment is particularly valuable for measurements on foods and personal care products. 

Another polyolefin of interest is polystyrene, a clear, brittle plastic that, by itself, is rarely used in composites. However, several copolymers and alloys of polystyrene with acrylonitrile or butadiene have been used with fiber glass or glass spheres to form composites (7). 

Hess, W. and Schonert, K., 1981. Brittle-Plastic Transition in Small Particles, In 1981 Powtech Conference on Particle Technology, Birmingham, EFCE Event No. 241, Rugby Institution of Chemical Engineers, pp. D2/I/1-D2/I/9. 

Heterogeneous compatible blends of preformed elastomers and brittle plastics are also an important route for the development of blends of enhanced performance with respect to crack or impact resistance. Polycarbonate blends with preformed rubber particles of different sizes have been used to provide an insight into the impact properties and the fracture modes of these toughened materials. Izod impact strength of the blends having 5-7.5 wt% of rubber particles exhibits best overall product performance over a wide range temperature (RT to -40°C) [151-154]. 

Since it measures the susceptibility of materials to plastic deformation (as contrasted with elastic deformation), hardness is very important for diagnosing the mechanical state of a material, in particular toughness. Purely elastic materials are brittle. Plasticity, by blunting cracks and other defects, allows metals and, to some extent ceramics, to tolerate small flaws and thereby become malleable and tough. 

Figure 7.1 Typical stress-strain curves for (a) a brittle plastic and (b) a tough plastic with yield point, showing the parameters used for the evaluation of degradation in tests...

And for the thread-cutting type o lower hoop stress o suitable for brittle plastics... 

Copolymerization allows the synthesis of an almost unlimited number of different products by variations in the nature and relative amounts of the two monomer units in the copolymer product. A prime example of the versatility of the copolymerization process is the case of polystyrene. More than 11 billion pounds per year of polystyrene products are produced annually in the United States. Only about one-third of the total is styrene homopolymer. Polystyrene is a brittle plastic with low impact strength and low solvent resistance (Sec. 3-14b). Copolymerization as well as blending greatly increase the usefulness of polystyrene. Styrene copolymers and blends of copolymers are useful not only as plastics but also as elastomers. Thus copolymerization of styrene with acrylonitrile leads to increased impact and solvent resistance, while copolymerization with 1,3-butadiene leads to elastomeric properties. Combinations of styrene, acrylonitrile, and 1,3-butadiene improve all three properties simultaneously. This and other technological applications of copolymerization are discussed further in Sec. 6-8. 

Finally, the use of low-molecular-weight species to improve flow properties called plasticizers normally reduces stiffness, hardness, and brittleness. Plasticization is usually restricted to amorphous polymers or polymers with a low degree of crystallinity because of the limited compatibility of plasticizers with highly crystalline polymers. Other additives, such as antioxidants, do not affect the mechanical properties significantly by themselves, but can substantially improve property retention over long periods of time, particularly where the polymer is subject to environmental degradation. 

A comparison of the abrasive wear by Bohm (1990) found that the hard and more brittle plastics, such as polyacetals, polyamide-imide, and polycarbonates, are less abrasion resistant than softer and tougher materials such as the polyethylenes and polyurethanes. Table 7.2 details some comparative... 

Brittle plastics may present difficulties with stamping and cutting operations. 

The product of this polymerization is polystyrene a clear, brittle plastic that is often used for inexpensive lenses, transparent containers, and styrofoam insulation. Polystyrene is also the major component of the resin beads that are used to make synthetic proteins. (See Section 24-11). 

Brittle, plastic, crisp, rubbery, spongy Smooth, coarse, powdery, lumpy, pasty Creamy, watery, soggy Sticky, tacky... 

Polyhydroxyalkonates (PHA) is a term given to a family of aliphatic polyesters produced by microorganisms that are fully biodegradable. They offer a wide array of physical properties that can range from stiff and brittle plastics to elastomers. 

Polystyrene is an amorphous, white and brittle plastic. Polystyrene has many applications due to its rigidity. Polystyrene is used for making products such as toys, display boxes, packaging material, egg cartons and styrofoam. 

Homopolymers of isobutylene and 0-pinene are, respectively, nonvulcanizable rubbers and brittle plastics. The projected structure of a random poly(isobutylene-co- -pinene) is of interest, since depending on the relative composition of the copolymer structure e.g.. 

Polystyrene, the familiar crystal-clear brittle plastic used to make disposable drinking glasses and, when foamed, the lightweight white cups for hot drinks, is usually made by free-radical polymerization. Commercially an initiator is not used because polymerization begins spontaneously at elevated temperatures. At lower temperatures a variety of initiators could be used (e.g., 2,2 -azobis-(2-methylpropionitrile) which was used in the free-... 

Figure 1.13 Stress-strain curves, (a) Synthetic fiber, like nylon-6,6, (b) Rigid, brittle plastic, like polystyrene, (c) Tough plastic, like nylon-6,6, (d) Elastomer, like lightly vulcanized natural rubber. (1 kgf/cm = 0.098 MN/m ).

MIPs are generally produced as opaque, vitreous, brittle, plastics. To be of practical use MIPs need to be reduced to a fine particulate material of uniform particle size. Typically, this is achieved by grinding processes, either by hand in a mortar and pestle or by mechanical means. The material is then sieved to give a powder of fixed upper particle size ( 25-45/im). Depending upon the final application, this material is then sedimented over a pre-determined time period to remove material that is too fine. The sedimentation step is particularly important if the MIP is to be used for HPLC applications where fine material causes high back-pressure and column blockage. 

Of the economical plastics mentioned above, GP polystyrene is becoming less popular, as it is one of the most brittle plastics unless it is impact modified. GP or (GPPS) polystyrene has good clarity, is highly permeable (compared with most other plastics) to moisture and gases, has poor heat and solvent resistance. It crazes then disintegrates in contact with isopropyl myristate (which is used in some pharmaceutical formulations). It is, however, an excellent material to mould (low shrinkage)... 

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