Plastic litter is widely acknowledged as a global environmental threat, and poor management and disposal lead to increasing levels in the environment. Of recent concern is the degradation of plastics from macro- to micro- and even to nanosized particles smaller than 100 nm in size. At the nanoscale, plastics are difficult to detect and can be transported in air, soil, and water compartments. While the impact of plastic debris on marine and fresh waters and organisms has been studied, the loads, transformations, transport, and fate of plastics in terrestrial and subsurface environments are largely overlooked. In this Critical Review, we first present estimated loads of plastics in different environmental compartments. We also provide a critical review of the current knowledge vis-a-vis nanoplastic (NP) and microplastic (MP) aggregation, deposition, and contaminant cotransport in the environment. Important factors that affect aggregation and deposition in natural subsurface environments are identified and c...

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Microplastics and Nanoplastics in Aquatic Environments: Aggregation, Deposition, and Enhanced Contaminant Transport

Biodegradation of poly(vinyl alcohol) based materials

Emulsion polymerization mechanisms and kinetics

Pure hydrogen production by PEM electrolysis for hydrogen energy

Proton exchange membrane fuel cells (PEMFCs) have recently passed the test or demonstration phase and have partially reached the commercialization stage due to the impressive worldwide research effort. Despite the currently promising achievements and the plausible prospects of PEMFCs, there are many challenges remaining that need to be overcome before PEMFCs can successfully and economically substitute for the various traditional energy systems. With the many promising research efforts in overcoming these challenges, the most important tools for the commercialization of PEMFCs will be the technical data and information from a real PEMFC application test. For these reasons, this paper introduces and discusses the remaining challenges and some of the latest research on the application test of PEMFC to real systems such as transportation, residential power generation and portable computers. In addition, this paper describes and summarizes the relative prospects and the competitive force of PEMFCs in these fields. These prospects primarily depend on stable and economical high-purity hydrogen supplies, the scale of application, the existence of more efficient competitive power sources and the social viewpoints such as the health and environment benefits as well as infrastructural aspects associated with traditional power supply and demand. The review shows that PEMFC have the most promising applications to buses, recreation vehicles, and lightweight vehicles. Without doubt, the technology for a stable supply of high-purity hydrogen along with the corresponding infrastructure is essential for the success of PEMFC in various application fields.

Applications of proton exchange membrane fuel cell systems

The oxidation behavior of cis-1,4-polyisoprene, emulsion polyisoprene, emulsion isoprene/styrene copolymers, and emulsion butadiene/styrene copolymers by heat aging or ultraviolet irradiation has been investigated from the change of gel fraction and molecular weight distribution. It was determined that the oxidation behavior of both isoprene and butadiene polymers is strongly dependent on the composition of the polymers as well as on the microstructure of the polymers. In the case of oxidation by heat aging, the probability ratio of chain scission to crosslinking of both isoprene and butadiene copolymers increases gradually with increasing styrene fraction. In the case of oxidation by ultraviolet irradiation, isoprene copolymers show a remarkable increase in the probability ratio of chain scission to crosslinking, whereas butadiene copolymers show substantially no change with increase in styrene fraction. It was also demonstrated that both isoprene and butadiene polymers show a greater tendency for crosslinking with oxidation by ultraviolet irradiation than with oxidation by heat aging.

Oxidation behavior of isoprene polymers and butadiene polymers

PURPOSE:To obtain the titled water-soluble polyvinyl alcohol (PVA) having improved viscosity stability of an aqueous solution thereof, by saponifying a copolymer consisting of a vinyl ester and two olefinically unsaturated monomers containing respective specific groups. CONSTITUTION:A copolymer obtained by copolymerizing (A) a vinyl ester, preferably vinyl acetate, with (B) an olefinically unsaturated monomer, e.g. vinyltrimethoxysilane, containing silyl groups and (C) an olefinically unsaturated monomer, e.g. N-(1,1-dimethyl-3-dimethylaminopropyl)acrylamide, containig ionic hydrophilic groups in the presence of (D) a radical initiator is saponified to give the aimed polyvinyl alcohol (PVA). The above-mentioned copolymerization is preferably carried out in the form of solution polymerization in the presence of a lower alcohol. Furthermore, the saponification is preferably carried out by using a solution of the copolymer in an alcohol in the presence of NaOH catalyst.

Takuji Okaya

Papers

Oxidation behavior of isoprene polymers and butadiene polymers

Production of modified polyvinyl alcohol having silyl group and ionic hydrophilic group

Filler fixing agent for paper

Polyvinyl alcohol paper processing agent