Volume 8 Issue 3

Paulownia wood (PW) flour was evaluated as a reinforcement for thermoplastic composites. Composites of high-density polyethylene in pellet form (HDPE), 25% by weight of PW, and either 0% or 5% by weight of maleated polyethylene pellets (MAPE), were produced by twin screw compounding followed by injection molding. Formulations of PW flour composed of specific particle sizes (≤590 to ≤75 µm) were also compared. Molded test composites were evaluated for their tensile, flexural, impact, and thermal properties. Composites made with PW and MAPE had significantly improved tensile and flexural properties compared to neat HDPE. The impact strength of all composites using MAPE was 30% improved over HDPE. Benchmarking PW composites to similar preparations of pine wood flour composites demonstrated that PW can produce a comparable and in some cases a superior bio-fiber composite. The effect of environmental exposure was examined by soaking tensile bars of HDPE-PW blends in distilled water for 28 days to observe changes in their physical and mechanical properties. Finally, differential scanning calorimetery and thermogravimetric analysis were conducted on PW composites to evaluate their thermal properties and the implications these may have on selecting processing conditions for the bio-fiber reinforcements.

Strand length, free-fall distance (FFD), and plate spacing was varied to control the strand alignment distribution of strandboard. To determine the strand angle distribution, photographs of strands were recorded as digital image data, and strand angle analysis was conducted using a modified von Mises distribution function. A part of this measurement was used as a reference for the alignment in the board produced. The results of strand alignment distributions showed that the k value was a function of strand length, FFD, and plate spacing. The k value can be improved by adjusting the plate spacing closer to the strand width, shortening the FFD, and using long strands. The power equation model can describe those relations. The bending properties and linear expansion (LE) were greatly affected by the FFD and the plate spacing. The use of low FFD and narrow plate spacing improved the bending properties. The decreasing bending properties in the parallel direction could be comparable to the increasing ones in the perpendicular direction. The contribution of bamboo strand in the longitudinal direction affected these results.

The effects of thermally grafting hydrolysed 3-aminopropyltriethoxysilane (APS) onto kenaf-derived cellulose and the influence of incorporating them into poly(lactic acid) (PLA) were investigated. Composites containing 30 wt.% cellulose (C) and silane-grafted cellulose (SGC) were melt-blended into PLA before being hot pressed into 0.3-mm films. The silane grafting of cellulose was confirmed via Fourier transform infrared spectroscopy (FTIR) with the presence of Si-O-Si, Si-O-cellulose, -Si-C-, and Si-O-C bonds, and –NH2 groups despite post ethanol washing. Using thermogravimetric analysis (TGA), it was determined that the thermal stability of the cellulose improved by 8 °C after silane grafting. As for the composites, PLA/SGC improved the thermal stability by 12 °C as compared to PLA/C. From differential scanning calorimetry (DSC), adding C into PLA slightly reduced the glass transition temperature, Tg, of the PLA from 59 °C to 57 °C, which remained unchanged with silane grafting. PLA displayed double melting peaks from its melt-recrystallization behaviour. While the final melting temperature at 150 °C was not affected, incorporating C and SGC influenced the intensity of the melting peaks. The significant reduction in crystallisation temperature from 113 °C to 102 °C and 105 °C, and the increase in crystallinity by almost two fold, indicated that cellulose was an effective nucleating agent.

Aging systems of wine brandies have been a target of investigation to reduce the costs and aging time. In this study, the extractives and Klason lignin contents of wood fragments used in the aging of wine brandies in stainless steel tanks were evaluated. Two types of wood fragments, known as staves and tablets, and two wood botanical species, Limousin oak (Quercus robur L. from the Limousin region of France) and Portuguese chestnut (Castanea sativa Mill.), with heavy toasting levels were used. The wood extractive and Klason lignin contents were analyzed before and 30 months after the aging of wine brandy. The results showed that the chestnut wood presented the highest content of extractives, while the Klason and total lignin contents were higher in the oak wood. A highly significant effect from the tablets was found on the extractives and Klason lignin contents, while the soluble lignin content was more affected by the staves. Oxygenation of the wine brandies during the aging process negatively affected the release of extractives and lignin from the wood to the brandy, and therefore will impact the overall quality of the brandy.

Wheat straws were split longitudinally using a specially designed straw splitter. Oriented structural boards made from the split straw strands were fabricated with polymeric diphenylmethane diisocyanate (pMDI) resin. The effects of the split straw strand length, resin content, and panel density on the properties of oriented structural straw board (OSSB) were investigated. Dimensional analysis showed that the average length of split straw strands after screening of the fines was 83.74 mm. More than 70% of the straw strands were in the range of 50 to 90 mm in length. The bending properties of the OSSB were highly related to the length of the split straws. The modulus of rupture (MOR) and modulus of elasticity (MOE) increased significantly as the split straw length was increased, particularly from 11 mm to 45 mm. The preferable length of the split straw was at least 40 mm to satisfy the MOE requirements. For a given pMDI content level, the internal bond (IB) strength increased linearly with an increase in panel density, which is consistent with previous results for wood-based panels. This study demonstrated that satisfactory OSSB can be made using approximately 3% pMDI at an average panel density of 640 kg/m³ to comply with the North American OSB products standard.

The impact of an aqueous ammonia pretreatment on the structural properties, delignifiability, and hydrolysability of wheat straw and corn stover was investigated. The results showed that the aqueous ammonia pretreatment had an excellent delignification ability and that the corn stover exhibited higher susceptibility to an aqueous ammonia attack than wheat straw. In total, 35.6% and 70.0% of the lignin in wheat straw and corn stover were removed, respectively, by the aqueous ammonia pretreatment at 75 ºC with 21% ammonia and a solid:liquid ratio of 1:10 for 20 h. Both lignin and polysaccharides in the corn stover exhibited higher susceptibility to aqueous ammonia than those in wheat straw. In addition, the hydrolysability of corn stover was more susceptible to aqueous ammonia than it was to wheat straw. A chemical structure analysis of different substrates showed that the aqueous ammonia pretreatment removed lignin, broke ester bonds between lignin and hemicelluloses, increased the specific surface area and crystallinity index, and, finally, enhanced the hydrolysis yield.

In light of the difficulties and disagreements in determining the property-processing structure relations of lignin-based polymers, dielectric analysis was used to identify the thermal and rheological characteristics of a lignin-based polycondensate and the pristine lignin. Using dielectric analysis, the pristine lignin with Mw=6000 g/mol, was clearly identified as giving the wet glass transition temperature (Tg,wet) and the evolution of gases (i.e., burning) at around 80 ºC to 125 ºC followed by subsequent cross-linking reactions over 150 ºC to give the dry glass transition temperature (Tg,dry) of lignin at around 130 ºC to 140 ºC. Connecting the lignin macromers using sequential condensation reactions with caprolactone and sebacoyl chloride, the lignin based polycaprolactone (LigPCL) polycondensates were synthesized as a thermoplastic polymer composed of lignin macromers and aliphatic polyester chains with Mw=10500 g/mol. The synthesized LigPCL presented good thermal stability and rheological melting behavior without evolving odor or fumes. In particular, the T2% (defined at 2% of weight loss) of the LigPCL and pristine lignin were 200 ºC and 80 ºC, respectively. The melt viscosity was measured at 103Pa.s at 120 ºC, ensuring facile melt-blending processing with various commodity polymers to be used in eco-friendly polymer composite development.

The performance of a process called sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL), which was carried out at high pH, was preliminarily investigated as a means of improving bagasse substrate enzymatic digestibility (SED). The lignin removal significantly affected the SED resulting from the SPORL-high-pH treatment. Lignin removal was found to be well-correlated with SED when the Boltzmann function was used to fit the curve. In this fitting curve, SED increased slowly initially and then rose up quickly with lignin removal (from 0% to 10%, and then from 10% to 35%) and finally reached an asymptotic value (80%, based on o.d. glucan in the pretreated substrate). Removing lignin to about 35% to 40% would be sufficient to significantly improve the SED of bagasse to the asymptotic value (80%) during enzymatic hydrolysis, while low cellulase and b-glucosidase (15 FPU/g and 22.5 CUB/g o.d. cellulose in the substrate, respectively) were loaded. Furthermore, combining this Boltzmann function and the SPORL-high-pH delignification model would be useful for predicting neutral-sulfite pretreated SED.

A Plackett-Burman design (PBD) combined with a steepest ascent approach is a powerful technique to screen the important operating parameters for the production of reducing sugars from sugarcane bagasse (SB). In this study, the most significant parameters (p< 0.05), as identified by PBD, were as follows: pretreatment duration, pH of pretreatment process, loading of enzyme cellulase, SB loading, and moisture content of SB. Analysis of variance (ANOVA) results showed that the model of reducing sugar productivity was able to provide a high correlation between the response and its parameters. Thus, the path of steepest ascent (PSA) method was used to assess the optimal region of variables for improved reducing sugar productivity from SB. The PSA analysis revealed that by treating 7.25 g of SB (with 84% moisture content) for 82.0 minutes at a pH of 8.8, followed by the addition of 34.0% v/w of cellulase, a reducing sugar productivity of 0.03 g/L could be achieved per hour during the enzymatic saccharification process.

In order to obtain “clean” liquefied lignin, selective liquefaction of lignin from bio-ethanol production residue (BEPR) was conducted using an aromatic solvent, furfuryl alcohol. The effects of liquefaction time, temperature, and liquid ratio on the liquefaction yield were investigated. The results indicated that with the increasing of liquefaction temperature (120 to 170 °C) or liquid ratio (3 to 5:1), the liquefaction yield of lignin (LYL) increased, respectively. Liquefaction times of 15 to 120 min had no significant effect on the liquefaction yield. When liquefaction was conducted at 170 °C for 15 min with a ratio of 5/1 liquefying solvent to raw material, the LYL reached its highest level of 80.23%. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Gel permeation chromatography (GPC) analyses confirmed that the liquefaction process had great selectivity for lignin. Ash and carbohydrates in the raw material could be removed as liquefied residue.