On the influence of molecular weight and crystallisation condition on the development of defect in highly drawn polyethylene

Longitudinal morphology of highly drawn high density polyethylenes has been investigated. Three grades of HDPEs with different molecular weights were used. Two different initial morphologies were obtained by quenching and slow cooling from the melt. The samples were drawn at 75 °C close to their breaking points and their longitudinal morphologies examined under SEM after etching. Two types of defects were observed. These are the structure containing a large number of parallel longitudinal etched pockets laid in the regions between almost parallel continuous transverse bands or ‘Pisa’ structure recently reported and transverse cracks. The appearance of these defects was found to correlate with molecular weight and thermal history of the samples. For all quenched samples, both Pisa structure and transverse cracks were observed. The number of transverse cracks was found to increase with increasing molecular weight. Apparently, the transverse cracks, which thought to limit the drawing to high draw ratios, can be retarded by drawing at higher temperature (100 °C). This suggests that the formation of transverse cracks relates to chain mobility and drawability of the materials. The Pisa structure was found to disappear from slowly cooled low molecular weight samples. For slowly cooled high molecular weight sample, the Pisa structure became less salient. It is suggested that the formation of Pisa structure is determined by molecular entanglement. Analysis of the band separation of the Pisa structure shows that there seems to be a characteristic value which depends on drawing temperature.     

Effect of processing parameters on the vulcanisation of natural rubber using glutaraldehyde

The process ability of vulcanising natural rubber using glutaraldehyde at low temperature has been studied. The main objective of this work is to improve the properties and stability of natural rubber (NR) using glutaraldehyde as a curing agent. In this study, the vulcanised samples were prepared systematically and compared with sulphur cured natural rubber vulcanisates. The influence of mole ratio of ammonia and glutaraldehyde, and the processing parameters (i.e. curing time and temperature) was investigated. The cured NR based on glutaraldehyde exhibited better hardness and thermal properties than that of the NR cured from conventional sulphur system. The experimental results reveal that the properties of glutaraldehyde cured NR can be developed with the proper additives combination and conditions adopted in the preparation. This cured system is very interesting due to it can be used for high temperature industrial applications. Moreover, it eases of processing at low temperature and cost.     

Properties and Stability of Protein-based Films from Red Tilapia (Oreochromis niloticus) Protein Isolate Incorporated with Antioxidant during Storage

Film from fish protein isolate (FPI) from red tilapia (Oreochromis niloticus) muscle prepared at pH 3 and incorporated with 100 ppm Trolox (FPIT film) was prepared and characterized in comparison with film prepared from unwashed mince film (UWM film) during storage of 40 days at room temperature (28–32°C). FPIT film had higher tensile strength (TS) and elongation at break (EAB) but lower water vapor permeability (WVP) than UWM film (p?<?0.05). During the storage, FPIT film had much lower thiobarbituric acid reactive substances value than UWM film. Furthermore, FPIT was more transparent and had no yellow discoloration, as evidenced by no change in b* and ΔE* values during the storage of 40 days. Both UWM and FPIT films were stabilized mainly by hydrogen bond, followed by hydrophobic interaction, disulfide bond, and nondisulfide covalent bond. Fourier transforms infrared spectra indicated that FPIT film contained the lower amount of lipids with the lower amplitude of amide B band, compared with UWM film. Higher degradation temperature (Td) was observed in FPIT film, indicating a greater protein–protein interaction in film matrix. FPIT film had smoother surface and cross-section than UWM film. After 40 days of storage, both films had the increase in TS and Td but lower EAB, WVP, and protein solubility. This was more pronounced in UWM film and was associated with the formation of nondisulfide covalent bond in the film network, most likely mediated by the interaction between protein and lipid oxidation products via Maillard reaction. Thus, film from FPI incorporated with antioxidant had the improved mechanical and physical properties without yellow discoloration.     

Characteristics and functional properties of gelatin from splendid squid (Loligo formosana) skin as affected by extraction temperatures

Gelatin was extracted from the skin of splendid squid (Loligo formosana) at different temperatures (50, 60, 70 and 80 °C) with extraction yield of 8.8%, 21.8%, 28.2%, and 45.3% (dry weight basis) for G50, G60, G70 and G80, respectively. Gelatin from the skin of splendid squid had a high protein content (∼90%) with low moisture (8.63–11.09%), fat (0.22–0.31%) and ash contents (0.17–0.68%). Gelatin extracted at higher temperature (G80) had a relatively higher free amino group content than gelatin extracted at lower temperatures (G50, G60 and G70) (P < 0.05). All gelatins contained α- and β-chains as the predominant components. Amino acid analysis of gelatin revealed the high proline and hydroxyproline contents for G50 and G60. FTIR spectra of obtained gelatins revealed the significant loss of molecular order of the triple-helix. The gel strength of gelatin extracted at lower temperature (G50) was higher than that of gelatins extracted at higher temperatures including G60, G70 and G80, respectively. The net charge of G50, G60, G70 and G80 became zero at pHs of 6.84, 5.94, 5.49, and 4.86, respectively, as determined by zeta potential titration. Gelatin extracted at higher temperature (G80) had the lower L* value but higher a* and b* values, compared with those extracted at lower temperatures (P < 0.05). Emulsion activity index decreased, whilst emulsion stability index, foam expansion and stability increased as the concentration (1–3%) increased (P < 0.05). Those properties were governed by extraction temperatures of gelatin. Thus gelatin can be successfully extracted from splendid squid skin using the appropriate extraction temperature.     

Influence of functional groups on properties of styrene grafted NR using glutaraldehyde as curing agent

Natural rubber grafted polystyrene (NR‐g‐PS) and natural rubber grafted polystyrene‐co‐methyl methacrylate (NR‐g‐P(S‐co‐MMA)) were prepared by emulsion polymerization technique using tert‐BuHP‐TEPA as a redox initiator to improve the thermal and mechanical stability of NR. Additional peaks appear in the Fourier‐transform infrared spectra at 695 and 1,732 cm^?1 confirms the formation of graft polymerization. The existence of functional groups on the grafted NR was also clearly confirmed from the morphology obtained from transmission electron microscopy analysis. The effect of curing on the mechanical and thermal properties of grafted NR has also been studied. Glutaraldehyde was used as the curing agent for the grafted and ungrafted NRs throughout the entire course of investigation. It was found that curing of grafted NR samples enhanced tensile strength, modulus, hardness, and thermal stability. Grafted NR showed the tensile strength values of 12 and 17 MPa for NR‐g‐PS and NR‐g‐P(S‐co‐MMA), respectively. Enhancement in thermal stability of NR was confirmend from the activation energy of degradation calculated based on thermogravimetric analyzer. The value of activation energy for NR (135.13 kJ/mol) was found to be increased to 147.89 kJ/mol (NR‐g‐PS) and 151.6 kJ/mol (NR‐g‐P(S‐co‐MMA)). The overall properties of NR have been strongly affected by the interaction and chain bundling between functional groups present in the grafted copolymer and the unsaturated chains in its structure. J. VINYL ADDIT. TECHNOL., 25:339–346, 2019. © 2019 Society of Plastics Engineers     

Properties of Bio-nanocomposite Films from Tilapia Skin Gelatin as Affected by Different Nanoclays and Homogenising Conditions

Fish gelatin films incorporated with hydrophilic and hydrophobic montmorillonite (mmt) nanoclays with the aid of homogenisation using different pressure levels (1,000 to 4,000 lb/in²) and passes (two and four) were characterised. Young’s Modulus, tensile strength and elongation at break of films decreased with increasing pressure levels and number of passes. High pressure homogenisation generally lowered the mechanical properties of nanocomposite films. Additionally, water vapour barrier property became poorer, when high pressure homogenisation was implemented. Films incorporated with hydrophobic nanoclay (Cloisite 20A) exhibited the lower water vapour permeability (WVP) than those with hydrophilic nanoclay (Cloisite Na⁺). Colour parameters (L*, a*, b* and ?E*) of nanocomposite films were affected to some degrees by homogenisation conditions. Transparency of films increased when homogenisation pressure and number of passes increased. As revealed by wide angle X-ray diffraction (WAXD) analysis, nanocomposite films prepared using homogenisation had exfoliated nanostructure, whilst those prepared without homogenisation exhibited intercalated nanostructure. Thermogravimetric (TGA) and differential scanning calorimetric (DSC) analyses indicated that thermal stability of nanocomposite films varied with homogenisation condition, being higher in these films than in those without nanoclay. Thus, homogenisation condition and hydrophobicity of nanoclay directly affected the properties of nanocomposite films from fish skin gelatin.     

Material properties of nanoclay PVC composites

Nanocomposites of poly(vinyl chloride) have been prepared using both hectorite- and bentonite-based organically-modified clays. The organic modification used is tallow-triethanol-ammonium ion. The morphology of the systems was investigated using X-ray diffraction and transmission electron microscopy and these systems show that true nanocomposites, both intercalated and exfoliated systems, are produced. The mechanical properties have been evaluated and the modulus increases upon nanocomposite formation without a significant decrease in tensile strength or elongation at break. Thermal analysis studies using thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis were conducted. Thermal stability of the PVC systems was assessed using a standard thermal process evaluating the evolution of hydrogen chloride and by color development through the yellowness index. Cone calorimetry was used to measure the fire properties and especially to evaluate smoke evolution. The addition of an appropriately-modified bentonite or hectorite nanoclay leads to both a reduction in the total smoke that is evolved, and an increase in the length of time over which smoke is evolved. Along with this, a reduction in the peak heat release rate is seen. It is likely that the presence of the clay in some way interferes with the cyclization of the conjugated system formed upon HCl loss.