Petroleum-based plastics Polyethylene

Despite its origin form the nature, PLA s good stiffness and strength has enabled it to compete with other existing chemically based commodity plastics. Previous study on the mechanical properties of neat PLA by Jacobsen et al. [1] showed that PLA has great potential to be a substitute polymer for petroleum based plastics. The respective values of mechanical properties of PLA [2] with comparison of other petroleum based plastics e.g. polypropylene (PP) [3], polystyrene (PS) [4], high density polyethylene (HOPE) [5], polyamide (PA6) [6] shown in Fig. 11.2. 

Generally speaking, bio-based plastics include starch-based plastics, protein (soybean protein) based plastics, and cellulose-blended plastics. They can also be blended with conventional plastics such as polyethylene (PE), polypropylene (PP), and poly(vinyl alcohol). However, such bio-based plastics are only partially biodegradable. The residual petroleum-based plastics remain as broken pieces, creating additional pollution. In addition, these plastics have intrinsic thermal and mechanical weaknesses, and they are now discouraged for applications. 

LCI can be used to calculate the environmental impacts of producing petroleum-based plastics. The LCI for petroleum-based plastics is based on ISO 14040 and 4044 and provided by the ACC for nine plastic resins and four polyurethane procurer resins. The cradle-to-gate analysis can provide a foundation for understanding the energy requirements, GHG emissions, waste generation, and pollution with the most common petroleum-based plastics. The LCA process for polyethylene terephtha-late (PET) plastic can be used as an example (ACC LCA 2011 Nine resins). 

Starch-based plastics can be classified as compostable if the additives are also biodegradable under industrial compost environment conditions. Starch can be an additive for petroleum-based plastics like polyethylene, polypropylene, polyurethane, and polyester. However, these starch-filled petroleum-based plastics are not included in this book since they would not biodegrade under industrial composting conditions and would not be recyclable with commercial mechanical recycling operations. 

Sustainable plastics are those plastics made with lower energy, lower carbon footprint, lower waste, and lower pollution than conventional plastics. Plastics that are made from plants or biobased sources and from recycled plastics can be made with lower energy, lower carbon footprint, lower waste, and lower pollution than conventional plastics. Biobased polyethylene, propylene, and PET can be made from sugarcane or other agricultural materials. Biobased plastics can be made with nearly identical mechanical properties as conventional petroleum-based plastics and can be manufactured on identical plastics processing equipment. 

Biodegradability of final products such as plastic bottles and films has become an important environmental concern. Where biodegradability is a desirable property, polyhydrox-yalkanoate- and polylactide-based plastics produced from bacterial processes are under development for replacement of poorly biodegradable polyvinyl, polyethylene, and other petroleum-based plastics. 

Plasticizers and Processing Aids. Petroleum-based oils are commonly used as plasticizers. Compound viscosity is reduced, and mixing, processing, and low temperature properties are improved. Air permeabihty is increased by adding extender oils. Plasticizers are selected for their compatibihty and low temperature properties. Butyl mbber has a solubihty parameter of ca 15.3 (f /cm ) [7.5 (cal/cm ) ], similar to paraffinic and naphthenic oils. Polybutenes, paraffin waxes, and low mol wt polyethylene can also be used as plasticizers (qv). Alkyl adipates and sebacates reduce the glass-transition temperature and improve low temperature properties. Process aids, eg, mineral mbber and Stmktol 40 ms, improve filler dispersion and cured adhesion to high unsaturated mbber substrates. 

Biodegradable biopolymers (BDP) are an alternative to petroleum-based polymers (traditional plastics). It will be important to find durable plastic substitutes, especially in short-term packaging and disposable applications. The continuously growing public concern concerning this problem has stimulated research interest in biodegradable polymers as alternatives to conventional non-degradable polymers such as polyethylene and polystyrene, etc. The economic value of renewable raw materials will increase to a significant extent [1] and induce new industrial activities [2,3]. 

H., and Harrison, S.T.L. (2007) Environmental analysis of plastic production processes comparing petroleum-based polypropylene and polyethylene with biologically-based poly-P-hydroxybutyric add using life cyde analysis./. Biotechnol, 130 (1), 57-66. 

Recently, the possibility of replacing petroleum-derived synthetic polymers with natural, abundant and low-cost biodegradable products has gained much interest in both academic and industrial fields. " For instance, the production of plastics in Europe reached 57 million tons in 2012, mostly divided between polyethylene, polypropylene, poly(vinyl chloride), polystyrene and poly(ethylene terephthalate) production. These fossil-based plastics were consumed and discarded into the environment, generating 10.4 million tons of plastic waste, most of which ended up in landfills (Figure 1). 

Life cycle assessment (LCA) can be used to determine the environmental impacts of producing the biobased polyethylene. The LCA will consider the energy and GHG emission for producing biobased polyethylene from the raw materials to the plastic pellet. The cradle-to-factory gate approach can he useful for plastic packaging, bags, and other products. The cradle-to-gate LCA of biobased polyethylene and petroleum-based polyethylene are Usted in Table 5.3 (Hunter et al. 2008). 

High density polyethylene (HDPE) is defined by ASTM D1248-84 as a product of ethylene polymerisation with a density of 0.940 g/cm or higher. This range includes both homopolymers of ethylene and its copolymers with small amounts of a-olefins. The first commercial processes for HDPE manufacture were developed in the early 1950s and utilised a variety of transition-metal polymerisation catalysts based on molybdenum (1), chromium (2,3), and titanium (4). Commercial production of HDPE was started in 1956 in the United States by Phillips Petroleum Company and in Europe by Hoechst (5). HDPE is one of the largest volume commodity plastics produced in the world, with a worldwide capacity in 1994 of over 14 x 10 t/yr and a 32% share of the total polyethylene production. 

There is every indication that the next several years will witness a continued rapid increase in the use of petroleum raw materials in the production of elastomers and plastics, and that the petroleum companies will become increasingly active, not only in providing the starting materials, but also in operating the chemical processes of converting them to the required monomers and polymers. The current increase in production of thermoplastic resins such as polystyrene, polyvinyl chloride, polyethylene, and acrylonitrile polymers is based on the development of widespread new applications at the consumer level, and the outlet for plastic materials in many of these uses is presently limited by the capacity to produce and process the resins rather than by consumer demand. 

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