Polymer blends, environmentally

Modern technology thrusts challenging demands on the performance capabilities of materials, including polymers and their blends. A new approach to the science and technology of polymer blends has emerged recently, i.e., polymer blends by design, rather than by availability. These polymeric materials must perform under strenuous mechanical, chemical, thermal and electrical conditions imposed by the requirements of a specific application. Service in these applications usually involves several criteria to be fulhlled without a loss of economic advantage. Indeed, performance requirements of polymer blends are often at the limit of the properties that can be achieved. Moreover, these materials are expected to endure complex environmental conditions for extended time. All these factors stress the need for in-depth studies of the properties and performance of polymer blends. 

Insufficient chemical resistance of a blend at times leads to its rejection for use in an aggressive chemical environment, although it possesses an excellent combination of mechanical properties. Thus chemical and solvent effects on polymer blends are important factors that frequently determine blends applicability. Attention has been given to chemical resistance of blends starting from the fundamental concept of the solubility parameters. Apart from the chemical and environmental restrictions, thermal resistance of a polymer blend is often a major criterion for its applicability. Thus, the thermal conductivity, heat capacity and heat deflection temperature of polymeric materials are discussed in separate sections. 

One of the more recent applications of polymer blends and alloys is in plastics recycling. The current solid waste crisis has resulted in public demands for industrial solutions that would result in a reduction of all landfilled solid waste, while minimizing alternate negative environmental impact. It has been perceived by the public that plastic materials account for the overwhelming majority of the landfilled solid mass, when plastics account for only approximately 7 wt% of 18 vol%. 

The selection of polymers and polymer blends for use as specific materials requires the consideration of how these will withstand the environmental conditions to which these will be subjected. The long term stability of a polymer will depend on its aging characteristics both physical and chemical. 

Cellulose blends with synthetic polymers also constitute an example of biodegradable polymer blends. Miscibility of cellulose with polyvinylpyrrolidone [Masson and Manley, 1991a], poly(4-vinyl pyridine) [Mason and Manley, 1991b], PAN [Nishio et al, 1987], PVAL [Nishio and Manley, 1988], and polyethyleneoxide (PEG) [Nishio et al., 1989] have been reported. Starch blends with commodity polymers have been commercialized as a low cost method to promote partial environmental degradability. While a defi-... 

Biodegradable constituents in polymer blends offer the advantage to design the desired property balance with a control of the environmental assimilation. The phase behavior will significantly affect the degradation rate and both miscible as well as immiscible blends will offer promise in the large packaging markets available for these materials. 

A particularly attractive application of hydrotropy in organic synthesis arises when the product is bulkier than the reactant, with the result that it has lower solubility than the reactant in the hydrotrope solution. Consequently, it selectively precipitates out of the reaction mixture and can be easily filtered out. Then the hydrotropic solution can be recycled, thus minimizing the environmental hazards associated with waste disposal. An important example is the synthesis of Diels-Alder adducts that act as flame retardants for polymer blends and formulations. One of these is also used in the manufacture of the pesticide Endosulfan. The reaction involves a diene such as hexachloro-pentadiene or anthracene and a dienophile such as p-benzoquinone or maleic anhydride. The following typical reaction carried out by Sadvilkar (1995) gave excellent results ... 

Tsuneizumi et al. [13] studied the chemical recycling of poly(lactic acid)-based polymer blends using environmentally benign catalysts, clay catalysts, and enzymes. Poly(L-lactic acid) (PLLA)-based polymer blends (e.g., PLLA/polyethylene [PE] and PLLA/poly(butylenes succinate) [PBS]) were degraded into repolymerizable oligomer. 

Many practical benefits can be obtained by blending polymers. Blending allows for the beneficial properties of two polymers to be combined in one material while shielding their mutual drawbacks. Deviations in the mle of mixing can lead to properties of the blend over and above those of its components. Thus, processibility, chemical and environmental resistance, adhesion, and mechanical properties of polymer blends are superior to those of their homopolymers. 

Green Nanocomposites from Renewable Resource-Based Biodegradable Polymers and Environmentally-Friendly Blends... 

Environmentally-Friendly Polymer Blends from Renewable Resources... 

Madbouly, S.A. and Lendlein, A. (2012) Degradable polyurethane/soy protein shape-memory polymer blends prepared via environmentally-friendly aqueous dispersions. Macromol. Mater. Eng., 297 (12), 1213-1224. 

The concern over environmental issues and sustainability has opened up another vibrant research field, namely, biobased and biodegradable polymer blends. An overview of major developments and recent trends in biodegradable blends with an emphasis on PLA blends are also discussed. This chapter closes with an outlook for the future of this important subject. 

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