Showing papers on "Commodity plastics published in 2001"

Polylactides: properties and prospects of an environmentally benign plastic from renewable resources

Abstract: Pressing environmental and economic concerns dictate the need to develop new synthetic macromolecules based on renewable resources. The vast majority of existing materials are based on non-renewable fossil resources that will eventually be extinguished. Manufacturing synthetic polymers and disposal by incineration produces CO 2 and contributes to global warming. For these reasons, poly(lactic acid) (PLA) polymers are of increasing commercial interest because they are derived from a renewable resources, sequester significant quantities of carbon dioxide relative to petrochemical based materials, conserve energy, and easily degrade. The mechanical properties of PLA are compared to other commodity plastics and it is shown that PLA closely resembles polystyrene. The effects of blending linear and branched chain architectures are discussed and it is shown that this provides a convenient method for controlling the elasticity and viscosity of the composite material without affecting mechanical or permeation properties. The melt rheology of high L content linear PLAs shows two unique features; they may be drawn to large Hencky strains without breaking and they exhibit considerable strain hardening. As a result, PLA is easily processed into fiber form. Due to the excellent combination of mechanical, rheological, and environmental properties, the prospects for widespread commercialization of PLA are excellent.

Polypropylene's continuing slump

Abstract: POLYPROPYLENE MIGHT BE THE closest the plastics industry will ever come to an all-purpose polymer. Because it is cheap and durable, it has consistently taken applications away from more expensive engineering polymers and less versatile commodity plastics, leading to the high growth rates the industry has enjoyed for many years. But just because polypropylene is an excellent polymer doesn't mean that the business is extremely profitable. In fact, the opposite has been true for the past several years. During this time, suppliers in North America and Europe have continually bombarded each other with excessive capacity increases because of high growth forecasts and an abundant supply of propylene. "Polypropylene hasn't been a good business to be in for the past 18 months to two years," says Steve Zinger, an analyst with Chemical Market Associates Inc. in Houston. "Since 1997, it has been a tough business, and now it's even worse." Zinger says rising energy prices have ...

The pyrolysis behavior of mixtures of commodity plastics with polyvinyl chloride in a thermogravimetric analyzer

Abstract: Waste plastics make up approximately 20 % of the volume of landfill material and almost 10 % of the weight. These products contain substantial energy recovery value, and also represent a potentially valuable source of feedstock raw material for additional plastics production. Controlled pyrolysis offers a method of converting raw, mixed waste plastics back into feedstock grade liquids by the application of heat in the absence of oxygen. However, chlorine from the thermal degradation of polyvinyl chloride (PVC) can contaminate the reclaimed liquids making them more difficult and expensive for processing, and also produce a corrosive atmosphere which makes processing more expensive. This paper reports on a study of the impact of PVC on the thermal degradation rates of other plastics including polypropylene (PP), polystyrene (PS), low-density polyethylene (LDPE), high density polyethylene (HDPE) and polyethylene terephthalate (PET) in a thermogravimetric analyzer (TGA). Commodity plastics were mixed at various ratios with PVC and analyzed by means of their degradation rates to determine the kinetic rate constants which were compared to the rates obtained for the pure plastics. The values of the kinetic parameters for the pure compounds were all very close to, or within the ranges obtained from the literature. The results indicated that the decomposition behavior of the mixtures differed from those of the pure polymers. These deviations were greatest for mixtures of PVC with polyethylene terephthalate where it was determined that the dehydrochlorination step of PVC catalyzes the decomposition of PET. Pyrolysis of mixtures of PVC and polystyrene at temperatures between 200°C and 350°C result in incomplete dehydrochlorination. This results in more chlorinated compounds being released at higher temperatures.