Wei-Hua Yao

Gasoline Permeation Resistance of Containers of Polyethylene, Polyethylene/Modified Polyamide and Polyethylene/Blends of Modified Polyamide and Ethylene Vinyl Alcohol

An investigation of the gasoline permeation resistance of polyethylene (PE), polyethylene/modified polyamide (MPA), and polyethylene/blends of modified polyamide and ethylene vinyl alcohol (MPAEVOH) bottles is reported. The gasoline permeation resistance improves slightly after blending EVOH barrier resins in PE matrices during blow-molding, wherein only broken and less demarcated EVOH laminas were found on the fracture surfaces of the PE/EVOH bottle. In contrast, much better permeation resistance and more clearly defined MPA and MPAEVOH laminas were found for PE/MPA and PE/MPAEVOH bottles, respectively. The gasoline barrier properties and MPAEVOH laminar structures of PE/MPAEVOH bottles improve and become more demarcated, respectively, as the MPA contents present in MPAEVOH resins increase. In fact, by using the proper composition, the gasoline permeation rate of PE/MPAEVOH bottles is about 450 and 3 times slower than that of the PE and PE/MPA bottles, respectively. These interesting gasoline barrier and morphological properties of PE, PE/MPA and PE/MPAEVOH were investigated in terms of melt shear viscosities and thermal properties of the base resins, and the chemical and physical amorphous phase structure present in their corresponding bottles.

Preparation and Characterization of Bioplastic-Based Green Renewable Composites from Tapioca with Acetyl Tributyl Citrate as a Plasticizer

Granular tapioca was thermally blended with poly(lactic acid) (PLA). All blends were prepared using a plasti-corder and characterized for tensile properties, thermal properties and morphology. Scanning electron micrographs showed that phase separation occurred, leading to poor tensile properties. Therefore, methylenediphenyl diisocyanate (MDI) was used as an interfacial compatibilizer to improve the mechanical properties of PLA/tapioca blends. The addition of MDI could improve the tensile strength of the blend with 60 wt% tapioca, from 19.8 to 42.6 MPa. In addition, because PLA lacked toughness, acetyl tributyl citrate (ATBC) was added as a plasticizer to improve the ductility of PLA. A significant decrease in the melting point and glass-transition temperature was observed on the basis of differential scanning calorimetry, which indicated that the PLA structure was not dense after ATBC was added. As such, the brittleness was improved, and the elongation at break was extended to several hundred percent. Therefore, mixing ATBC with PLA/tapioca/MDI blends did exhibit the effect of plasticization and biodegradation. The results also revealed that excessive plasticizer would cause the migration of ATBC and decrease the tensile properties.

Argon-Plasma Treatment for Improving the Physical Properties of Crosslinked Cotton Fabrics With Dimethyloldihydroxyethyleneurea-Acrylic Acid

In this study, argon plasma treatment was added to the traditional pad-dry-cure process between dry and cure treatment. This new process was assign as pad-dry-plasma-cure. The crosslinking agent was a mixture of dimethyloldihydroxyethyleneurea (DMDHEU) and acrylic acid (AA). The results showed that argon plasma treatment could increase the bonded crosslinking agent (nitrogen content). Dry crease recovery angle (DCRA), wet crease recovery angle (WCRA) and tensile strength retention (TSR) of pad-dry-plasma-cure-finished fabrics were higher than that of traditional pad-dry-cure finished fabrics at a given value of nitrogen content. Additionally, it was found that the number of crosslinks per anhydroglucose unit (CL/AGU) and the length of crosslinks of pad-dry-plasma-cure-finished fabrics were higher than that of traditional pad-dry-cure-finished fabrics at a same resin concentration in the pad bath. DCRA, WCRA and TSR values of pad-dry-plasma-cure-finished fabrics were higher than that of pad-dry-cure-finished fabrics at a same CL/AGU value. The pad-dry-plasma-cure process is thought to be excellent for improving the physical properties and decreasing the formaldehyde release of the finished cotton fabrics.

Biocompatibility and characterization of polylactic acid/styrene-ethylene-butylene- styrene composites

Polylactic acid (PLA)/styrene-ethylene-butylene-styrene (SEBS) composites were prepared by melt blending. Differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WXRD) were used to characterize PLA and PLA/SEBS composites in terms of their melting behavior and crystallization. Curves from thermal gravimetric analysis (TGA) illustrated that thermostability increased with SEBS content. Further morphological analysis of PLA/SEBS composites revealed that SEBS molecules were not miscible with PLA molecules in PLA/SEBS composites. The tensile testing for PLA and PLA/SEBS composites showed that the elongation at the break was enhanced, but tensile strength decreased with increasing SEBS content. L929 fibroblast cells were chosen to assess the cytocompatibility; the cell growth of PLA was found to decrease with increasing SEBS content. This study proposes possible reasons for these properties of PLA/SEBS composites.

Crosslinking of Cotton Cellulose in the Presence of Alpha-Amino Acids: Part II: Reaction Kinetics of the Mixed Reagents

Two kinds of alpha-amino acids are used to combine with dimethylol-dihydroxyethyleneurea (DMDHEU) as crosslinking agents, and the specific rate constants and other activation parameters are discussed. From the results, we find that the rate constants for the various crosslinking agent systems are in the order of DMDHEU > DMDHEU-aspartic acid > DMDHEU-glutamic acid. The energies needed to crosslink are in the rank of DMDHEU-glutamic acid > DMDHEU-aspartic acid > DMDHEU. The values of enthalpy and entropy for DMDHEU are lower than those for DMDHEU-alpha-amino acids, and enthalpy values for DMDHEU are significantly lower than those for DMDHEU-alpha-amino acids. The data of various activation parameters reveal that the reaction state of DMDHEU-alpha-amino acids is different from that of DMDHEU. Additionally, the reactions between aluminum sulfate and aspartic acid are confirmed by infrared spectra.

Crosslinking of cotton cellulose in the presence of alpha-aminoacids. Part III: Pore structures

Two kinds of alpha-amino acids were used to combine with dimethylol-dihydroxyethyleneurea (DMDHEU) as crosslinking agents. It was found that the values of equilibrium dye absorption, dyeing rate constant and the structural diffusion resistance constant for various combinations of crosslinking agents were in the rank of DMDHEU-glutamic acid > DMDHEU-aspartic acid > DMDHEU alone at the same dyeing temperature. The activation energies of dyeing for the three crosslinked fabrics were ranked as follows: DMDHEU > DMDHEU-aspartic acid > DMDHEU-glutamic acid. The patterns of fiber cross-section obtained by scanning electron microscopy showed that the degree of the swelling of the DMDHEU crosslinked fiber was somewhat lower than that of DMDHEU-alpha-amino acid crosslinked fibers. From this it was concluded that the fabrics crosslinked with the DMDHEU-alpha-amino acid combinations had a larger pore structure.

Physicochemical properties and molecular weight characterisation of porcine dermal collagen digested under varying conditions with clostridium histolytic collagenase

Abstract Porcine dermal collagen is successfully digested by clostridium histolyticun collagenases (CHC) at varying compositions and conditions. Collagen fragments thus prepared, with significantly low molecular weight but visible denaturation temperatures and/or triple helix structures, may be useful for clinical applications. As evidenced by Sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) and gel permeation chromatography (GPC) analyses, relatively high molecular weights of α1, α2 subunit, β1 ,β2 dimmers and γ trimmers of the collagen fragments gradually disappear as their incubation temperature and/or time values increase. The time values corresponding to the disappearance of sigmoid plots in the denaturation curves, denaturation endotherm in DSC thermograms and γ bands in SDS-PAGE patterns of digested collagen specimens are the same and reduce significantly as their incubation temperatures increase. Fourier transform infra-red analyses results suggest that the percentages of preserved triple helix structures present in collagen molecules of digested collagen specimens also reduce significantly with increasing the incubation temperature and time values. Possible reasons accounting for the degradation, denaturation and physicochemical properties of digested porcine dermal collagens are explored in this study.

Inner distribution and deposition of crosslinked cotton fabrics using a steeped process

The steeped procedure was used to investigate the physical properties and crosslinking structure. It was found that the values of the N content, dry crease recovery angle (DCRA), and wet crease recovery angle (WCRA) of the treated fabrics with any specific steeped procedure were higher than those of normally treated fabrics. For a given number of crosslinks per anhydroglucose unit (CL/AGU) the crosslinking length (CL length) values for the steep-pad-dry-cure process were higher than those for pad-dry-cure process. All the DCRA and WCRA values for the steep-pad-dry-cure process were higher than those for pad-dry-cure process at a given resin concentration, tensile strength retention (TSR), and CL/AGU. The surface distribution of crosslinking agent on the finished fabrics for pad-dry-cure process was higher than that for the steep-paddry-cure process. The expansion degree of the steep-pad-dry-cure treated fiber is slightly higher than that of the pad-dry-cure process. Those results obtained from pictures of SEM, crosslinking structure, and surface distribution of fibers/fabrics treated by the two processes clearly show that the crosslinking agents could diffuse and self-condensate in the treated fabrics to obtain an inner and longer crosslink under the steeped procedure so as to have good DCRA and WCRA.