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

To make clear the reason of unsuitability of poly(vinyl alcohol) (PVA) protective colloid for the emulsion polymerization of conjugated monomers, a model experiment of emulsion polymerization of methyl methacrylate (MMA) was carried out with ammonium persulfate (APS) or azobis(isobutyronitrile) (AIBN) initiators, where a small amount of MMA (1/100th of the concentration compared with ordinary emulsion polymerization) was employed. This corresponds to the initial stage of the emulsion polymerization. Grafting of MMA onto PVA took place remarkably irrespective of the kind of the initiators. Formation of homo-poly(MMA) was observed to a small extent. The formation of new emulsion particles smaller than 100 nm continued to increase to almost the end of the polymerization. PVA molecules in the grafted polymer are supposed to act as stabilizers of newly formed particles. From kinetic treatment using the experimental data, the important issues were derived as follows. Firstly, the sulfate anion radical from APS is much more reactive than the isobutyronitrile radical from AIBN in terms of hydrogen abstraction from PVA. Secondly, high grafting ability of the latter initiator system, notwithstanding the much lower reactivity in the hydrogen abstraction compared with the APS system, is attributed to the relative reactivity of the primary radicals, i.e., hydrogen abstraction reaction from PVA to initiation reaction with MMA. The much slower rate of addition of the isobutyronitrile radical to the monomer compared with that of hydrogen abstraction from PVA facilitates the grafting, although the rate constant of hydrogen abstraction is far smaller than that with the sulfate anion radical by 10−4 times.

Effect of initiators on grafting in the initial stage of the emulsion polymerization of methyl methacrylate using poly(vinyl alcohol) as a protective colloid

To realize the mechanism of particle formation followed by the grafting of styrene (St) onto poly(vinyl alcohol) (PVA) more precisely, we investigated the influence of additives on model experiments of emulsion polymerizations in 1 ml styrene (St) per 100 ml water at 70 °C using PVA as a protective colloid. In the case of a standard system without additive, experimental results indicate new particle formation, and that 30% of St feed and 30% of the PVA used were grafted. The sulfate radical seldom enters into particles but reacts with PVA, forming the PVA radical that yields the grafting of St onto PVA. The experimental results are thought to arise from a hydrogen abstraction from PVA with a sulfate radical. The addition of low-molecular-weight alcohol, such as isopropyl alcohol (i-PrOH) and n-propyl alcohol (n-PrOH), strongly affected the mechanism of particle formation in terms of a decrease in grafting, due to competition between hydrogen abstraction from PVA and the alcohols with a sulfate radical. Surprisingly, the addition of a low-reactive alcohol, such as t-butyl alcohol (t-BuOH), also resulted in the particle formation with a decrease in grafting, influenced the polymerization locus to be a monomer droplets dispersed by t-BuOH, and confirmed homogeneous nucleation with the increase in the solubility of St in the aqueous phase.

Effect of additives on the initial stage of emulsion polymerization of styrene (St) using poly(vinyl alcohol) as a protective colloid

PURPOSE: A novel polyvinyl ester based polymer, containing specific fluorine- containing monomeric units, having improved water and oil repellency, and useful as a surface treating agent, etc. CONSTITUTION: A polyvinyl ester based polymer obtained by copolymerizing a vinyl ester, e.g. vinyl acetate, vinyl formate or vinyl laurate, with a fluorine- containing monomer expressed by formula IWIII [R 1 and R 2 are H, lower alkyl, COOR (R is H or lower alkyl), CONR 2 or COOM (M is alkali metal or ammo nium); Rf is fluorine-containing group; X 1 , X 2 and X 3 are linking group], and containing preferably 0.02W30mol% one or more corresponding fluorine- containing monomeric units expressed by formula IWIII. COPYRIGHT: (C)1986,JPO&Japio

Polyvinyl ester based polymer having fluorine-containing group

The present invention provides a process for producing easily on an industrial scale a polyvinyl ester having a high degree of polymerization and PVA having a high degree of polymerization derived by saponification form such a polyvinyl ester. The process of this invention makes it possible to produce the desired product especially even when the polymerization is carried out until a high conversion to polymer is attained, as well as even when the polymerization is suspended while the conversion to polymer is still low.

Process for producing polyvinyl ester having a high degree of polymerization and process for producing polyvinyl alcohol having a high degree of polymerization

PURPOSE: To obtain the titled polymers having uniform and narrow distribution of molecular weights industrially and advantageously, by feeding a mercaptan continuously to reactors in the respective stages of a multi-stage continuous polymerization apparatus at a specific ratio, carrying out the solution polymerization of vinyl acetate, and saponifying the resultant polymer. CONSTITUTION: In polymerizing vinyl acetate in a solution in methanol with a multi-stage continuous polymerization apparatus consisting of n (n≥1) reactors, a mercaptan, e.g. n-dodecyl mercaptan or 2-mercaptoethanol, is fed continuously to the respective reactors in the respective stages according to the formula {[X]is the molar concentration of the mercaptan; x is the rate of polymerization; Cx is the chain transfer coefficient to the mercaptan; 0 [X] m is the molar concentration of the mercaptan fed to the m-th reactor based on the total amount of the vinyl acetate and the methanol fed to the first reactor; [X] m is the molar concentration of the mercaptan in the m-th reactor; 1≤m≤n}. Preferably, the mercaptan is not newly fed to the n-th reactor. COPYRIGHT: (C)1982,JPO&Japio

Takuji Okaya

Papers

Effect of initiators on grafting in the initial stage of the emulsion polymerization of methyl methacrylate using poly(vinyl alcohol) as a protective colloid

Effect of additives on the initial stage of emulsion polymerization of styrene (St) using poly(vinyl alcohol) as a protective colloid

Polyvinyl ester based polymer having fluorine-containing group

Process for producing polyvinyl ester having a high degree of polymerization and process for producing polyvinyl alcohol having a high degree of polymerization

Continuous preparation of polyvinyl acetate and polyvinyl alcohol having low polymerization degree