Authenticating bioplastics using carbon and hydrogen stable isotopes - An alternative analytical approach.

RATIONALE: A combination of stable carbon (δ13 C) and hydrogen (δ2 H) isotope ratios and carbon content (% C) was evaluated as a rapid, low-cost analytical approach to authenticate bioplastics, complementing existing radiocarbon (14 C) and Fourier transform infrared (FTIR) analytical methods. METHODS: Petroleum- and bio-based precursor materials and in-market plastics were analysed and their δ13 C, δ2 H and % C values were used to establish isotope criteria to evaluate plastic claims, and the source and biocontent of the samples. 14 C was used to confirm the findings of the isotope approach and FTIR analysis was used to vertify the plastic type of the in-market plastics. RESULTS: Distinctive carbon and hydrogen stable isotope ratios were found for authentic bio-based and petroleum-based precursor plastics, and it was possible to classify in-market plastics according to their source materials (petroleum, C3, C4, and mixed sources). An estimation of C4 biocontent was possible from a C4-petroleum isotope mixing model using δ13 C which was well correlated (R2 = 0.98) to 14 C. It was not possible to establish a C3-petroleum isotope mixing model due to δ13 C isotopic overlap with petroleum plastics; however, the addition of δ2 H and % C was useful to evaluate if petroleum-bioplastic mixes contained C3 bioplastics, and PLS-DA modelling reliably clustered each plastic type. CONCLUSIONS: A combined dual stable isotope and carbon content approach was found to rapidly and accurately identify C3 and C4 bio-based products from their petroleum counterparts, and identify instances of petroleum and bio-based mixes frequently found in mislabelled bioplastics. Out of 37 in-market products labelled as bioplastic, 19 were found to contain varying amounts of petroleum-based plastic and did not meet their bio-based claims.

Comparison of Micropore Distribution in Cell Walls of Softwood and Hardwood Xylem.

The porosity of wood cell walls is of interest for both understanding xylem functionality and from a wood materials perspective. The movement of water in xylem generally occurs through the macroporous networks formed in softwood by bordered pits and in hardwood by the intervessel pits and open conduits created by vessels and perforation plates. In some situations, such as cavitated xylem, water can only move through the micropores that occur in lignified tracheid and fiber cell walls; however, these micropore networks are poorly understood. Here, we used molecular microscopy analysis of radiata pine (Pinus radiata) and red beech (Nothofagus fusca) to determine the distribution of micropores in the secondary walls and middle lamellae of tracheids and fibers in relation to cell wall composition. Using two different types of probe, we identified a greater porosity of secondary cell walls and a reduced porosity of the middle lamella. Areas of reduced porosity were observed in the outer regions of the secondary cell wall of both tracheids and fibers that appear unrelated to lignification or the distribution of cellulose, mannan, and xylan. Hardwood fiber cell walls were less lignified than those of softwood tracheids and showed greater accessibility to porosity probes. Vessel cell walls were comparable to those of fibers in terms of both porosity and lignification. Lignification is probably the primary determinant of cell wall porosity in xylem. The highly lignified middle lamella, and lumen surface, act as a barrier to probe movement and, therefore, water movement in both softwood and hardwood.

Structural features affecting the enzymatic digestibility of pine wood pretreated with ionic liquids.

Pretreating lignocellulosic biomass with certain ionic liquids results in structural and chemical changes that make the biomass more digestible by enzymes. In this study, pine wood was pretreated with 1-ethyl-3-methylimidazolium chloride/acetate ([C2 mim]Cl and [C2 mim][OAc]) at different temperatures to investigate the relative importance of substrate features, such as accessible surface area, cellulose crystallinity, and lignin content, on enzymatic digestibility. The ionic liquid pretreatments resulted in glucan conversions ranging from 23% to 84% on saccharification of the substrates, with [C2 mim][OAc] being more effective than [C2 mim]Cl. The pretreatments resulted in no delignification of the wood, some loss of cellulose crystallinity under certain conditions, and varying levels of increased surface area. Enzymatic digestibility closely correlated with accessible surface area and porosity measurements obtained using Simons' staining and thermoporosimetry techniques. Increased accessible surface area was identified as the principal structural feature responsible for the improved enzymatic digestibility.

Wide-angle x-ray scattering and solid-state nuclear magnetic resonance data combined to test models for cellulose microfibrils in mung bean cell walls.

A synchrotron wide-angle x-ray scattering study of mung bean (Vigna radiata) primary cell walls was combined with published solid-state nuclear magnetic resonance data to test models for packing of (1→4)-ß-glucan chains in cellulose microfibrils. Computer-simulated peak shapes, calculated for 36-chain microfibrils with perfect order or uncorrelated disorder, were sharper than those in the experimental diffractogram. Introducing correlated disorder into the models broaden the simulated peaks but only when the disorder was increased to unrealistic magnitudes. Computer-simulated diffractograms, calculated for 24- and 18-chain models, showed good fits to experimental data. Particularly good fits to both x-ray and nuclear magnetic resonance data were obtained for collections of 18-chain models with mixed cross-sectional shapes and occasional twinning. Synthesis of 18-chain microfibrils is consistent with a model for cellulose-synthesizing complexes in which three cellulose synthase polypeptides form a particle and six particles form a rosette.