R. W. Truss

The anaerobic degradability of thermoplastic starch: polyvinyl alcohol blends: potential biodegradable food packaging materials.

A systematic study on the anaerobic degradability of a series of starch:polyvinyl alcohol (TPS:PVOH) blends was performed to determine their fate upon disposal in either anaerobic digesters or bioreactor landfills. The aims of the study were to measure the rate and extent of solubilisation of the plastics. The extent of substrate solubilisation on a COD basis reached 60% for a 90:10 (w/w) blend of TPS:PVOH, 40% for 75:25, 30% for 50:50 and 15% for PVOH only. The rate of substrate solubilisation was most rapid for the 90:10 blend (0.041 h(-1)) and decreased with the amount of starch in the blend in the following order 0.034 h(-1)(75:25); 0.023 h(-1)(50:50). The total solids that remained after 900 h were 10 wt.% (90:10); 23 wt.% (75:25); 55 wt.% (50:50); 90 wt.% (0:100). Starch containing substrates produced a higher concentration of volatile fatty acids (VFAs) and biogas, compared to the 0:100 substrate. The major outcome was that PVOH inhibited the degradation of the starch from the blend.

Insect mandibles-comparative mechanical properties and links with metal incorporation

A number of arthropod taxa contain metals in their mandibles (jaws), such as zinc, manganese, iron, and calcium. The occurrence of zinc and its co-located halogen chlorine have been studied in relation to the mechanical properties and shown to be linked in a direct fashion with increasing concentration. Hardness along with elastic modulus (stiffness) has also been linked to zinc and halogen concentration in some marine polychaete worms. The metal appears to be incorporated within the biological matrix, possibly bonding with proteins. However, the comparative advantage of metal inclusion has not been tested. It is possible that without metals, alternative mechanisms are used to achieve hardness of equal value in similar ‘tools’ such as mandibles. This question has direct bearing on the significance of metal hardening. In the present article, we compare across mandibles from six termite species, including samples with major zinc concentration, minor manganese, and no metals. Nanoindentation, electron microscopy, and electron microanalysis are used to assess metal concentration, form, and mechanical properties. The data demonstrate that termite mandibles lacking metals when fully developed have lower values for hardness and elastic modulus. Zinc is linked to a relative 20% increase in hardness when compared with mandibles devoid of metals. The similar transition metal, manganese, found in minor concentrations, is not linked to any significant increase in these mechanical properties. This raises the question of the function of manganese, which is as commonly found in insect mandibles as zinc and often located in the same mandibles.

Effect of flyash content and coupling agent on the mechanical properties of flyash-filled polypropylene

Flyash to 20 wt% was added to polypropylene and an ethylene/propylene copolymer with and without the addition of a maleic anhydride grafted polypropylene coupling agent. The tensile mechanical properties were assessed and the fracture toughness measured by using notched impact specimens. The modulus of the materials increased with the addition of the filler and further increased with the addition of the coupling agent while the yield stress decreased with the addition of 10 wt% filler and no coupling agent but was unchanged from the matrix when the coupling agent was added. Elongation to break was significantly less in those composites to which the coupling agent had been added. Scanning electron microscopy showed that bonding between the matrix and the filler was significantly improved by the addition of the coupling agent and this appeared to hinder the drawing mechanisms in the polymer. The fracture toughness in the copolymer based composites was seen to decrease with filler content.

Characterization of stress-whitening of tensile yielded isotactic polypropylene

The microstructure of tensile tested isotactic polypropylene (iPP) specimens was studied by grey level measurement, scanning electron microscopy (SEM), differential scanning calorimetry (d.s.c.) and X-ray diffraction (XRD). SEM revealed that the necked regions of specimens in which stress-whitening had occurred as determined by the grey level measurement had craze-like structures which were parallel to the drawing direction. D.s.c. analysis showed that the necked regions of tensile specimens which remained transparent after yielding had an additional low-melting temperature peak. However, no additional melting peaks were found in the stress-whitened specimens. Inspection of the XRD patterns indicated that, apart from its original α-crystallites (a monoclinic structure) which were broken and reoriented after drawing, there was no new types of crystals formed in the transparent specimens. It was found by quantitative XRD analysis that the crystallites were broken into finer pieces in the whitened specimens than in the transparent ones.

Effect of the ionic liquid 1-ethyl-3-methylimidazolium acetate on the phase transition of starch: Dissolution or gelatinization?

This work revealed that the interactions between starch, the ionic liquid 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]), and water might contribute to the phase transition (gelatinization, dissolution, or both) of native starch at reduced temperature. Using mixtures of water and [Emim][OAc] at certain ratios (7.2/1 and 10.8/1 mol/mol), both the gelatinization and dissolution of the starch occur competitively, but also in a synergistic manner. At lower [Emim][OAc] concentration (water/[Emim][OAc] molar ratio≥25.0/1), mainly gelatinization occurs which is slightly impeded by the strong interaction between water and [Emim][OAc]; while at higher [Emim][OAc] concentration (water/[Emim][OAc] molar ratio≤2.8/1), the dissolution of starch is the major form of phase transition, possibly restricted by the difficulty of [Emim][OAc] to interact with starch.

Tensile deformation behaviour of ABS polymers

Several grades of ABS polymer have been tested in uniaxial tension over a temperature range from 293 K (20° C) to 198 K (−80° C). Effects of strain-rate and temperature on the yield stress have been explored and the magnitude of the activation volumes and activation energies derived. Additionally, the volume strain and the longitudinal strain have been monitored simultaneously, from which data the contribution of crazing to the total deformation of the specimens has been obtained.

Understanding the structural disorganization of starch in water-ionic liquid solutions

Using synchrotron X-ray scattering analyses and Fourier transform infrared spectroscopy, this work provides insights into the solvent effects of water : [C2mim][OAc] solutions on the disorganization of a starch semi-crystalline structure. When a certain ratio (10.2 : 1 mol/mol) of water : [C2mim][OAc] solution is used, the preferential hydrogen bonding between starch hydroxyls and [OAc](-) anions results in the breakage of the hydrogen bonding network of starch and thus the disruption of starch lamellae. This greatly facilitates the disorganization of starch, which occurs much easier than in pure water. In contrast, when 90.8 : 1 (mol/mol) water : [C2mim][OAc] solution is used, the interactions between [OAc](-) anions and water suppress the solvent effects on starch, thereby making the disorganization of starch less easy than in pure water. All these differences can be shown by changes in the lamellar and fractal structures: firstly, a preferable increase in the thickness of the crystalline lamellae rather than that of the amorphous lamellae causes an overall increase in the thickness of the semi-crystalline lamellae; then, the amorphous lamellae start to decrease probably due to the out-phasing of starch molecules from them; this forms a fractal gel on a larger scale (than the lamellae) which gradually decreases to a stable value as the temperature increases further. It is noteworthy that these changes occur at temperatures far below the transition temperature that is thermally detectable as is normally described. This hints to our future work that using certain aqueous ionic liquids for destructuration of the starch semi-crystalline structure is the key to realize green processes to obtain homogeneous amorphous materials.

Unique zinc mass in mandibles separates drywood termites from other groups of termites

Previously, the presence of metals in arthropod mandibles has been linked with harder cuticle, and in termites, a 20% increase in hardness has been found for mandibles containing major quantities of zinc. The current study utilises electron microscopy and energy-dispersive X-ray microanalysis to assess incidence and abundance of metals in all extant subfamilies of the Isoptera. The basal clades contain no zinc and little to no manganese in the cutting edge of the mandible cuticle, suggesting that these states are ancestral for termites. However, experimentation with mandibles in vitro indicates the presence of some elements of the cuticular biochemistry necessary to enable uptake of zinc. The Termopsidae, Serritermitidae, Rhinotermitidae and Termitidae all contain minor quantities of manganese, while trace to minor quantities of zinc occur in all except the Serritermitidae. In contrast, all Kalotermitidae or drywood termites contain major levels of zinc in the mandible edge. Diet and life type are explored as links to metal profiles across the termites. The presence of harder mandibles in the drywood termites may be related to lack of access to free water with which to moisten wood. Scratch tests were applied to a set of mandibles. The coefficient of friction for Cryptotermes primus (Kalotermitidae) mandibles, when compared with species from other subfamilies, indicates that zinc-containing mandibles are likely to be more scratch resistant.

Effect of chemical structure on the wear behaviour of polyurethane-urea elastomers

The wear behaviour of a series of polyurethane-urea elastomers of two hardness levels, 83/90 Shore A, made with two different curatives and a range of stoichiometries was studied using two different methods. In a high-speed slurry erosion test, wear was higher in the harder polymers but in a Dry Sand Rubber Wheel test, the softer polymers underwent greater wear. This change in rankings of the polymers was associated with a change in the wear mechanism from cutting and gouging in the slurry test to a fatigue mechanism in the Dry Sand Rubber Wheel test. In both wear tests and for the two levels of hardness tested, polymers cured with MBOCA were more wear-resistant than those cured with ETHACURE which was linked to a higher level of crosslinking in the MBOCA polymers. Decreasing the stoichiometry of the softer 83 Shore A ETHACURE polymers introduced crosslinks into these polymers and there was a corresponding increase in the wear resistance. High surface temperatures occurred in the high speed slurry tests, and these probably resulted from hysteresis in the polymers. Softening of the polymers may also have contributed to the variation in performance of the different polymers.

Interlaminar and intralaminar fracture toughness of uniaxial continuous and discontinuous carbon fibre/epoxy composites

The interlaminar and intralaminar fracture toughness of a continuous carbon fibre/epoxy composite and an aligned discontinuous carbon fibre (DISCO)/epoxy composite have been measured using the compact tension and double cantilever beam test geometries. The DISCO composite was found to have a slightly greater misalignment of the fibres from the average fibre direction and this misalignment was found to increase both the initiation fracture toughness and to a greater extent the propagation fracture toughness. The increase in fracture toughness in the DISCO samples was due to fibres bridging the crack and this has been modelled as if the bridging fibres provide an increase in compressive stress across the crack analogous to a craze at the crack tip.