Resource or waste? A perspective of plastics degradation in soil with a focus on end-of-life options.

Recent attention surrounds bisphenol-A (BPA) due to potential estrogen mimicry and human health hazards. The public's negative reactions to these concerns threaten the commercial use of BPA requiring the global polymer community to investigate suitable replacements for commercial products that demand very good thermal and mechanical properties from BPA. This review highlights four classes of polymers that often utilize BPA for enhancing specific properties: polycarbonates, polyesters, epoxies and polyimides. A compilation of recent efforts involving the design of BPA-free polymers is provided. Alternative monomers include 2,2,4,4-tetramethyl-1,3-cyclobutanediol and isosorbide, and emerging polymers that exhibit acceptable thermal and mechanical properties are discussed. Copyright © 2012 Society of Chemical Industry

A perspective on emerging polymer technologies for bisphenol‐A replacement

Polycarbonate (PC), one of the leading engineering plastics, suffers from deterioration under harsh environmental conditions. It is sensitive to the effects of light (UV) radiation, to thermal degradation, and to the attack of hot water, due to hydrolysis. By exposure of various commercial PC grades—at various molecular weights and stabilization—to either natural or accelerated conditions, a maximum lifetime of three years was predicted for the best-behaving grades. The criterion for failure was mainly based on loss of ductility in tensile tests, as well as loss of optical clarity and chain scission. Hot water has a significant effect on the performance of PC samples, and this is considered to be its greatest weakness. Degradation after exposure at various temperatures (without UV or humidity) leads to estimation of a temperature-endurance index, that may serve as a practical limiting criterion for polymer life expectancy.

Life expectation of polycarbonate

Blends of polyamide 6 (PA6) and polycarbonate (PC) were prepared in a Brabender mixer, at 240°C, applying long mixing time, for 45 min. It was observed that the morphology and the mechanical properties tend to resemble those of a homogeneous material as the mixing time and PA6 concentration increase. This is attributed to chemical reactions taking place between the two homopolymers. Acidolysis, amidolysis, and aminolysis, catalyzed by the terminals and the amide groups of the polyamide, should in principle be possible. Our results indicate that the aminolysis is the main process, inducing simultaneously scission of PC chains and formation of PC-PA6 copolymer chains. The latter act as interfacial agents between incompatible PA6 and PC, improving the mechanical properties of PA6-rich blends, in agreement with the predictions of some theoretical models assuming good phase interpenetration. © 1992 John Wiley & Sons, Inc.

Blends of polyamide 6 and bisphenol-A polycarbonate. Effects of interchange reactions on morphology and mechanical properties

The durability of polylactide (PLA) blended with polycarbonate (PC) was assessed by exposure to conditions of elevated temperature and humidity over a period of several weeks. Mechanical performance, moisture absorption, chemical composition, and thermal properties were monitored as a function of continuous conditioning at 70°C and 90% relative humidity (RH). All PLA and PC/PLA blends showed significant moisture absorption and hydrolysis, resulting in degradation of properties. Furthermore, while the addition of PC was intended to improve the durability of the blend over neat PLA, it was found that the hydrolysis products of PLA accelerated the degradation of PC itself. This study shows for the first time the hydrolysis behavior of PC/PLA blends in an increasingly acid environment during heat and humidity conditioning. These injection-molding grades of PLA-based resins are currently not suitable for use in applications that require long-term durability in environments subject to elevated temperature and humidity, such as automotive interiors. Further material formulation work is required before use in injection-molded applications for automotive. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Durability of polylactide‐based polymer blends for injection‐molded applications

Elevated temperatures and high humidity decrease the molecular weight and impact strength of polycarbonate. Hydrolysis of injection molded polycarbonate (PC) bars stored in glass containers at 85°C and 96% relative humidity (RH) produced brown surface crystals within 30 days. Aging of PC bars at 96% RH and temperatures of 70°C and lower for longer periods of time formed a brown liquid coating on the PC. X-ray, DSC, and GPC measurements indicated that about 70 wt% of the surface crystals were bisphenol A (BPA). The remaining portion of hydrolysis products appeared to be higher molecular weight oligomers of BPA. The brown liquid was composed of supercooled liquid BPA, BPA oligomers, and water. Initial growth of BPA on the surface of a PC bar took place at the interface between the PC and the glass wall of the container. Apparently a water soluble extract from the glass container accelerated the hydrolytic degradation of PC; nevertheless, hydrolysis of PC occurred in the absence of glass—although at a slower rate. Hydrolysis studies were carried out on several commercial PC formulations. The PC resin containing only a heat stabilizer was least affected. Of the fiame retardant grades, the brominated PC hydrolyzed less rapidly than these particular compositions containing alkali metal sulfonic acid salts. A glass fiber reinforced PC was less stable than its unfilled parent compound. A hydrolytic stabilizer was ineffective against the attack of water under these conditions.

Hydrolysis of polycarbonate to yield BPA

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Hydrolysis of polycarbonate to yield BPA