A.J. van Reenen

The Effect of Wood Species on the Mechanical and Thermal Properties of Wood—LLDPE Composites

Different wood species can be expected to affect the properties of wood—polymer composites (WPCs) differently, as they have different chemical compositions. The chemical composition (cellulose, lignin, hot water, and ethanol/ cyclohexane extractive contents) of acacia, eucalyptus, pine, and oak and the morphological properties such as wood fiber length distribution were determined in order to investigate this effect. Composites of linear low-density polyethylene and 10 wt% of each of the wood species were prepared, using polyvinyl alcohol-co-ethylene as a compatibilizer. Significant differences were found between the wood species in terms of both chemical composition and wood fiber length distribution. These affected the properties of the WPCs in different ways. Use of acacia resulted in a WPC with superior mechanical properties and thermal stability compared with the other species, due to its higher cellulose and lignin contents and a favorable wood fiber length distribution; however, acacia composites also showed a higher water absorption rate due to the higher cellulose content. We also found that WPCs containing wood species with a high lignin and extractive content, such as acacia and oak, had a higher resistance to UV degradation.

Polyvinyl alcohol and modified polyvinyl alcohol reverse osmosis membranes

Abstract A study was conducted on the insolubilization of polyvinyl alcohol. Polyvinyl alcohol was regarded as a stable material for the formation of gel layer base membranes, which could then be further modified to produce RO membranes with good salt retention. This paper reports the study of the in situ insolubilization of polyvinyl alcohol membranes. Laboratory and field trial experiments were conducted with some of these membranes, and the results are reported on. Some results of the first chemically modified polyvinyl alcohol membranes are also given.

Poly(vinyl alcohol) gel sub-layers for reverse osmosis membranes. III. Insolubilization by crosslinking with potassium peroxydisulphate

Abstract Both flat-sheet and tubular composite reverse osmosis (RO) membranes were prepared by depositing aqueous solutions of poly(vinyl alcohol) [PVA] and potassium peroxydisulphate [K 2 S 2 O 8 ] on asymmetric poly(arylether sulphone) [PES] substrate membranes. Heat treatment of the PVA coatings resulted in crosslinking through carbon-carbon bond formation. The crosslinked PVA gels were highly hydrophilic and maintained their integrity in acidic and alkaline environments. The effect of PVA concentration, molecular mass and degree of hydrolysis, K 2 S 2 O 8 concentration, curing temperature and curing time on RO properties was studied. A simple manipulation of one or more variables resulted in membranes with widely differing RO properties. Long-term exposure of membranes to a CaSO 4 slurry feed indicated a remarkable resistance to abrasion. RO tests on a real industrial effluent have underscored the stability and chemical resistance of these PVA membranes. The insolubilized PVA coatings were intended to serve as hydrophilic gel sub-layers on which salt-retention barriers could be formed by interfacial polycondensation. For this purpose, high permeate fluxes are required. The latter can be obtained by adjusting coating solution compositions and fabrication conditions. These PES-PVA gel-layer composite membranes could also function as medium-retention, high-flux RO membranes, even in the abasence of an interfacially formed salt-retention barrier.

Poly(vinyl alcohol) gel sub-layers for reverse osmosis membranes. II: Insolubilization by crosslinking with poly(methyl vinyl ether-alt-maleic anhydride)

Abstract Composite reverse osmosis (RO) membranes were prepared by depositing aqueous compatible blends of poly(vinyl alcohol) [PVA] and poly(methyl vinyl ether- alt -maleic anhydride) [MVE- alt -MAH] on flat-sheet asymmetric poly(arylether sulphone) [PES] substrate membranes. Insolubilization of the polymer blend films was accomplished by the formation of interchain ester crosslinks during heat treatment. The crosslinked films were intended to serve as hydrophilic gel sub-layers on which ultrathin salt-retention barriers could ultimately be formed by interfacial polycondensation. The RO properties (salt retention, permeate flux) of PVA-based membranes prepared in the absence and presence of H 2 SO 4 catalyst were measured at various pH values of the feed solution (2,000 mg/l NACl). The highest permeate fluxes were obtained when membranes were cured in the presence of acid catalyst. The salt-retention and water permeability characteristics varied with the pH of the feed solution. This was attributed to the different degrees of ionization of the first and second carboxyl groups of the maleic acid residues in hydrolysed MVE- alt -MAH at different pH values. Different ratios of PVA and MVE- alt -MAH were evaluated. A PVA: MVE- alt -MAH molar ratio of 3.5: 1 resulted in gellayer membranes with sufficiently high water permeabilities for application as gel sub-layers in RO membranes.

Reverse osmosis membranes prepared from potassium peroxydisulphate-modified poly(vinyl alcohol)

Abstract Poly(vinyl alcohol) (PVAL) was modified and insolubilized by reaction with potassium peroxydisulphate (K2S2O8) and used to make reverse osmosis (RO) membranes on tubular poly(arylether sulphone) (PES) ultrafiltration (UF) substrates. Prior to making the membranes, aqueous solutions of PVAL and K2S2O8 were aged. The effects of solution maturation times on the salt retentions and permeate fluxes of the resultant membranes were determined. Increased maturation times were found to lead to membranes with higher salt retentions. The K2S2O8-crosslinked PVAL membranes were also tested with an industrial effluent. Changes which took place in the maturing PVAL K 2 S 2 O 8 solutions were characterized by viscometry, UV spectroscopy, 1H- and 13C-NMR spectroscopy, and pH measurements. Only the most important results of these analyses are reported here.

Polyethylene oxide (PEO)-hyaluronic acid (HA) nanofibers with kanamycin inhibits the growth of Listeria monocytogenes

Listeria monocytogenes is well known to cause prosthetic joint infections in immunocompromised patients. In this study, polyethylene oxide (PEO) nanofibers, containing kanamycin and hyaluronic acid (HA), were prepared by electrospinning at a constant electric field of 10kV. PEO nanofibers spun with 0.2% (w/v) HA and 1% (w/v) kanamycin had a smooth, bead-free structure at 30-35% relative humidity. The average diameter of the nanofibers was 83±20nm. Attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy indicated that kanamycin was successfully incorporated into PEO/HA matrix. The presence of kanamycin affects the thermal properties of PEO/HA nanofibers, as shown by differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA). The kanamycin-PEO-HA nanofibers (1mg; 47±3μg kanamycin) inhibited the growth of L. monocytogenes EDGe by 62%, as compared with PEO-HA nanofibers, suggesting that it may be used to coat prosthetic implants to prevent secondary infections.

Hyaluronic acid-coated poly(D,L-lactide) (PDLLA) nanofibers prepared by electrospinning and coating

Hyaluronic acid nanofibers (HA/PDLLA) were prepared by coating electrospun poly(D,L-lactide) (PDLLA) with different concentrations of HA. Highest concentration of HA deposited onto PDLLA nanofibers (17% per weight) were obtained by coating with 0.3% (w/v) HA. Coating with 0.5% (w/v) and 0.1% (w/v) HA yielded a deposit of 3.8% and 3% per weight, respectively. All nanofibers were 300–400 nm in diameter and microscopically homogeneous in structure, with traces of HA clearly visible on the surface and in-between the fibers. Examination of the nanofibers with Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) revealed changes in the properties of the nanofibers when coated with 0.3% (w/v) HA. Release of HA from HA/PDLLA fibers were at a linear and constant rate. One possible application for HA/PDLLA is the coating of surfaces, such as medical implants, to prevent secondary microbial infections during recovery from surgery.

Surfactin-loaded polyvinyl alcohol (PVA) nanofibers alters adhesion of Listeria monocytogenes to polystyrene

Surfactin-loaded polyvinyl alcohol (PVA) nanofibers were spun using gravity electrospinning. Scanning electron microscopy (SEM) images showed that nanofibers spun with surfactin are free from bead formation and uniform in diameter. The average nanofiber diameters were decreased (273±39nm, 259±39nm and 217±33nm) with increasing levels of surfactin (0.5, 1.0 and 1.5%, w/v) into PVA (10%, w/v). The 10% (w/v) PVA had average fiber diameter of 303±33nm. Atomic force microscopy (AFM) analysis showed that fibers spun with surfactin are not smooth as PVA fibers. The surface average roughness (Sa) estimated for surfactin loaded nanofibers (0.5%: 19.0nm, 1.0%: 20.4nm and 1.5%: 20.7nm) was higher as compared with PVA (10%:15.8nm). Scanning transmission electron microscopy (STEM) showed no matrix differences between PVA and surfactin-loaded PVA nanofibers. Fourier transform infrared (FTIR) microscopy revealed uniform distribution of surfactin in PVA. Based on differential scanning calorimetry (DSC) analyses, surfactin decreased the crystallinity of PVA during spinning. No antimicrobial activity was detected against methicillin-resistant Staphylococcus aureus (MRSA) strain Xen 30, Listeria monocytogenes EDGe, Escherichia coli Xen 14, and Pseudomonas aeruginosa PA01. However, the adhesion of L. monocytogenes to polystyrene in presence of surfactin-loaded nanofibers decreased significantly (OD595: 0.012±0.001) as compared with control (OD595: 0.022±0.002), suggesting that these nanofibers may be used in wound dressings or in the coating of prosthetic devices to prevent biofilm formation and secondary infections.

Dynamically formed hydrous zirconium (IV) oxide-polyelectrolyte membranes VII. Poly(acrylic acid-co-vinyl acetate) and poly(acrylic acid-co-vinyl alcohol) membranes: The effect of feed salt concentration on membrane properties

Abstract A series of poly(acrylic acid co-vinyl acetate) (I) copolymers, as well as a series of poly(acrylic acid-co-vinyl alcohol) (II) copolymers were synthesized. Hydrous zirconium (IV) oxide- (I) and (II) dynamic membranes were formed. The effect of feed salt concentration on the rejection and flux of these membranes was investigated and is reported on.

Dynamically Formed Hydrous Zirconium (IV) Oxide-Polyelectrolyte Membranes. V. Non-Homogeneous Poly (Acrylic Acid-Covinyl Alcohol) Membranes: Rejection and Flux Properties and the Treatment of Coal Gasification Waste Water

Abstract A non-homogeneous poly(acrylic acid—covinyl alcohol) copolymer (I) was synthesized. This copolymer was used as polyelectrolyte in a dynamically formed hydrous zirconium (IV) oxide—polyelectrolyte membrane. The resultant Zr(I) membrane gave salt rejection figures exceeding 99% and flux values of 2500 lmd. A set of these Zr(I) membranes was used to treat a coal gasification wastewater in a laboratory experiment, and the membranes rejected a wide variety of constituents satisfactorily.