Water-soluble polymers

Ecofriendly biopolymers and composites: Preparation and their applications in water-treatment

Over the past few decades, the term polymer has been repeatedly used in several industries for their immense characteristics in different applications. Polymers and their composites which were prepared from chemical monomer sources turned out to be potentially harmful to the environment due to their tedious degradation process. Biopolymers are natural substitutes for synthetic polymers which can be efficiently extricated from natural sources. They are predominantly available as polymeric units as well as monomeric units that are linked covalently. These environment-friendly biopolymers and their composites can be categorized based on their numerous sources, different methods of preparation and their potential form of usage. They were found to be biocompatible and biodegradable which make them exceptionally useful in environment based applications, mainly in the process of water treatment, both potable and wastewater. Further, the biopolymer and biopolymer composites easily fit into different parts of the treatment process by acting as filtration media, adsorbents, coagulants and as flocculants. The primary focus of this review is to provide a comprehensive information of biopolymers and biopolymer composites from synthesis to their usefulness for their productive application in water treatment processes. On the whole, it can be substantiated that the biopolymers were identified to play a notable adversary to the synthetic polymers in treating waters with an indispensable need for an elaborative study in the production of the biopolymers.

Preparation of Miscible PVA/PEG Blends and Effect of Graphene Concentration on Thermal, Crystallization, Morphological, and Mechanical Properties of PVA/PEG (10 wt%) Blend

Water-soluble polymers such as poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG) and their nanocomposites with graphene were prepared by using a solution mixing and casting technique. The effect of different PEG loadings was investigated to determine the optimum blend ratio. The films were characterized using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analyzer (TGA) methods. Also, the mechanical properties including tensile strength and elongation at break were measured using a universal tensile testing machine. FTIR results confirmed the formation of the H-bond between PEG and PVA. DSC studies revealed that PEG has a significant plasticization effect on PVA as seen by the drop in the glass transition temperature (Tg). The blend with 10 wt% PEG loading was found to be the optimum blend because of good compatibility as shown by FTIR and SEM results and improved thermal properties. PVA/PEG (10%) nanocomposites were prepared using graphene as a nanofiller. It was found that the elongation at break increased by 62% from 147% for the PVA/PEG (10%) blend to 209% for the nanocomposite with graphene loading of 0.2 wt%. The experimental values of tensile strength were compared using the predictive model of Nicolais and Narkis.

Sustainable enzymatic preparation of polyaspartate using a bacterial protease

Diethyl l-aspartate was polymerized by a bacterial protease from Bacillus subtilis (BS) in organic solvent at a temperature between 30 and 50 degrees C to yield alpha-linked poly(ethyl l-aspartate) having an M(w) of up to 3700 and a maximum polymer yield of 85%. The best polymerization conditions were the 40 degrees C polymerization of diethyl l-aspartate using 30% protease BS containing 4.5 vol % water in acetonitrile for 2 days. Poly(ethyl l-aspartate) was readily depolymerized by the enzyme into the oligomeric and monomeric l-aspartate in aqueous acetonitrile. Poly(sodium aspartate) prepared by the saponification of poly(ethyl l-aspartate) was readily biodegradable by activated sludge obtained from the municipal sewage treatment plant. Also, poly(sodium aspartate) was depolymerized by the hydrolase enzyme into the monomeric aspartate. These results may indicate the sustainable chemical recycling and biorecycling of this polymer.

A hazard ranking of organic contaminants in refinery effluents

An environmental hazard ranking model (benchmark ranking model) has been developed and used for the ranking of organic compounds likely to be found in petroleum refinery effluents. The hazard function is essentially a multiplication of variables for toxicity (as LC50), octanol-water ratio (Kow), soil adsorption (Koc), solubility (S), and half-life (T1/2). The final score is obtained by taking the logarithm of the hazard and normalizing the values from 1-10. It is a benchmark ranking (BR) approach in the sense that the hazard for chemicals with essentially unknown environmental behaviors may be compared with the hazard for chemicals with well-known behaviors. In general, debates on water pollution have focused on non-polar (hydrophobic) compounds whereas polar (water soluble) compounds have attracted much less attention and regulation. This study focuses on a number of the polar compounds (methyl-tertiary-butyl-ether [MTBE], morpholine, metanolamine and others) since there are indications that some of these may cause environmental damage. While non-polar compounds receive the highest score in the study, the combination of frequently large volumes, low biodegradability, low treatability, and analytical detection problems suggest caution when neglecting polar compounds in waste minimization pursuits and in the assessment of environmental hazard and damage.