Academic literature on the topic 'Polymers Polymers Polymers Polystyrene Polystyrene Plastic foams'

The global increase in production of plastic and accumulation in the environment is becoming a major concern especially to the aquatic life. This is due to the natural resistance of plastic to both physical and chemical degradation. Lack of biodegradability of plastic polymers is linked to, amongst other factors, the mobility of the polymers in the crystalline part of the polyesters as they are responsible for enzyme interaction. There are significantly few catabolic enzymes that are active in breaking down polyesters which are the constituents of plastic. The synthetic polymers widely used in petroleum-based plastics include polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polyurethane (PUR), polystyrene (PS), polyamide (PA) and polyethylene terephthalate (PET) being the ones used mostly. Polymers with heteroatomic backbone such as PET and PUR are easier to degrade than the straight carbon-carbon backbone polymers such as PE, PP, PS and PVC.

Use of supercritical fluids (SCFs), particularly supercritical carbon dioxide, as alternative solvents in polymer synthesis and processing is a rapidly growing research area with successful industrial applications (McCoy, 1999). In some cases, the need for alternative solvents is based on environmental concerns, with regulations mandating replacement solvents. An environmentally mandated example is the 1995 ban of the use of chlorofluorocarbons (CFCs) as physical blowing agents in the manufacture of polymeric foams after CFCs were classified as class-I-ozone-depleting substances (ODPs). Among the alternative blowing agents are gases like CO2 and N2 and refrigerants such as 1,1-difluoroethane (R152a) and 1,1,1,2-tetrafluoroethane (R134a). Under the foaming conditions, at temperatures above the glass transition temperature of a polymer, and at pressures required for flow of highly viscous polymer melts, these alternative blowing agents are frequently supercritical. When polymers are formed into final products by various melt-processing techniques, such as extrusion, injection molding, blow molding, foaming, and spin-coating, extremely high melt viscosity presents a major difficulty. A common method to moderate the processing conditions is to add a liquid solvent or plasticizer to the melt. Solvents and plasticizers lower the glass transition temperature, Tg, of the polymer so that the polymer can be made to flow at lower pressures and temperatures. Replacing liquid solvents with SCFs presents unique processing advantages. Higher diffusivity and lower viscosity of SCFs, compared with liquid solvents, increase rates of dissolution and mixing. The properties of polymer–SCF solutions are tunable via pressure or temperature changes, thus allowing efficient downstream separations. Most importantly, dissolution of an SCF produces very large reductions in melt viscosity compared with a liquid solvent dissolved in the melt. Whether the interest in using SCFs in polymer synthesis and processing is driven by environmental concerns or processing advantages, it is important to understand the rheological behavior of polymer–SCF mixtures. In this chapter, we describe rheological measurements of polymer melts containing dissolved gases for two polymers, polydimethylsiloxane (PDMS) swollen with CO2 at 50 °C and 80 °C and polystyrene (PS) swollen with CO2, R152a, and R134a at 150 °C and 175 °C.

Plastics that are degraded by microbial or enzymatic activity are known as biodegradable plastics. Biodegradable plastics are an alternative to conventional plastics that are chemically synthesized and are responsible for causing environmental pollution due to unwanted accumulation occurring via disposal practices. There was a serious need to introduce biodegradable plastics in the market since the level of plastic pollution in the air, water, and soil has reached its threshold values. The non-biodegradable plastics are increasingly accumulating in the environment, which can be a threat to the planet in the coming future. This chapter provides detailed insight into biodegradables polymers, mostly aliphatic polyesters that are considered as a solution against synthetic plastic. It also gives brief information on the current scenario of plastic biodegradation, recent advancements, opportunities, and future challenges. Also, it comprises precise strategies currently used at a laboratory scale to enhance biodegradation of classical synthetic plastics (e.g., polyethylene, polystyrene, etc.). Moreover, the factors affecting the biodegradation process and the characterization techniques being employed to assess degradation extent are also discussed. The overall work focuses on thrust areas to be improved concerning environmental safety and sustainable vision.

Tailoring the rheological properties of polymers is important for practical applications such as the stabilization of polymer emulsions, blends, and foams. Nanomaterial (i.e. Carbon Nanotubes, Carbon Nanofibers, Dendrimers, and Carbon Black) are an excellent way to modify the mechanical, thermal, electrical, and optical properties of materials. This paper presents steady shear and linear viscoelastic oscillation testing of three polymers: Polyethylene (PE); Polypropylene (PP); and Polystyrene (PS). These polymers were studied in bulk form and as composites containing designated volume fraction

Traditional micromanufacturing has been developed for semiconductor industry. Selected micro electrical mechanical systems (MEMS) have been successfully developed and implemented in industry. Since current MEMS are designed for manufacture using microelectronics processes, they are limited to two-dimensional profiles and semiconductor based materials. Such shape and material constraints would exclude many applications that require biocompatibility, dynamic stress, and high ductility. New technologies are sought to fabricate three dimensional microcomponents using robust materials for demanding