Time filter

Source Type

Nar M.,University of North Texas | Rizvi H.R.,University of North Texas | Dixon R.A.,University of North Texas | Dixon R.A.,Oak Ridge National Laboratory | And 5 more authors.
Carbon | Year: 2016

Plant-sourced carbon has a valuable impact on zero carbon footprint materials for automotive, aerospace, water filtration and other applications. A new lignin, poly-(caffeyl alcohol) (PCFA, also known as C-lignin), has recently been discovered in the seeds of the vanilla orchid (Vanilla planifolia). In contrast to all known lignins which are comprised of polyaromatic networks, the PCFA lignin is a linear polymer derived almost totally from caffeyl alcohol monomers linked head to tail into benzodioxane chains via the 'endwise' radical coupling reactions that typify lignification. In this paper we investigate carbon fiber formed from this linear C-lignin and compare it to a Kraft lignin. The PCFA was extracted and electrospun into fibers without additional modification or blending of polymers. Nanoindentation shows an increase in transverse and axial modulus for PCFA carbon by around 250% and 25% respectively as compared to Kraft lignin carbon. Raman spectroscopy results indicate higher graphitic structure for PCFA carbon than that from Kraft lignin, as seen from G/D ratios of 1.92 vs 1.15 which was supported by XPS and TEM results. Size exclusion chromatography indicates a polydispersity index (PDI) for PCFA of 1.6 as compared to 2.6 for Kraft lignin and Zeta potential measurements show higher ionic conductivity for Kraft lignin as compared to PCFA reflecting higher impurities. The results indicate a new bio-source for carbon fibers based on this newly identified linear lignin. © 2016 Published by Elsevier Ltd.

Sobczak L.,Competence Center for Wood Composites and Wood Chemistry Wood us | Bruggemann O.,Johannes Kepler University | Putz R.F.,Competence Center for Wood Composites and Wood Chemistry Wood us
Journal of Applied Polymer Science | Year: 2013

Numerous strategies to improve the fiber-matrix interaction in natural fiber composites (NFCs) and wood polymer composites (WPCs) have been proposed and investigated. We have reviewed literature on polyolefin-based NFCs and WPCs to get an overview of the current state of the art of compatibilization methods. Those are classified in two categories here, namely fiber-based strategies and matrix-based strategies. Although this issue has been covered by several reviews before, as yet no work exists that is focused on polyolefin-based NFCs and WPCs. Furthermore, a ranking of the compatibilization methods based on their effects on material properties such as tensile/flexural strength and modulus, impact strength and water absorption, allows for an assessment of the efficiency of the various methods. As to the fiber-based strategies, silanes, maleated polyolefins (MA-POs), mercerization and acetylation are most thoroughly investigated. Silanes are most effective judged by achievable material property improvements, allowing for increases in tensile and flexural strength of more than 100%. Among the matrix-based strategies, MA-POs and isocyanates are most prominent in the literature. The first class enables the more significant material improvements, with reported increases of tensile and flexural strength of 132% and 85%, respectively. While strengths can be enhanced by many compatibilization methods, moduli, and impact strength (notched in particular) are in most cases improved to a lesser degree or even reduced. Especially, the last point calls for further attention, because impact strength is still a weak point of NFCs and WPCs. Copyright © 2012 Wiley Periodicals, Inc.

D'Amico S.,Competence Center for Wood Composites and Wood Chemistry Wood us | Muller U.,Competence Center for Wood Composites and Wood Chemistry Wood us | Berghofer E.,University of Natural Resources and Life Sciences, Vienna
Journal of Applied Polymer Science | Year: 2013

In this study the adhesive bond strength of different wheat gluten modifications and the relationship between molecular weight and adhesive strength was examined. Guanidine hydrochloride and sodium hydroxide were used as denaturation and dispersing agent. Additionally wheat proteins were hydrolyzed by alkaline conditions and enzymes. Effects of different treatments were observed by viscosity measurements and gel electrophoresis. Wood lap joints were prepared with modified proteins and tensile shear strength was tested under dry and wet conditions. In situ hardening of different formulations was analyzed by means of DMA with two-layered specimens in a three-point bending test set-up. Higher solubility had no positive effect on dry bonding strength and wet bonding strength was even reduced. Depending on the degree of hydrolysis, significant improvement of adhesive bond strength was observed. Copyright © 2013 Wiley Periodicals, Inc.

Sobczak L.,Competence Center for Wood Composites and Wood Chemistry Wood us | Steiner M.,Competence Center for Wood Composites and Wood Chemistry Wood us | Schausberger A.,Johannes Kepler University | Haider A.,Competence Center for Wood Composites and Wood Chemistry Wood us
Polymer Composites | Year: 2013

Six commercial polypropylene (PP) homopolymer grades, ranging from 2 to 125 g/10 min in MFR (230°C/2.16 kg), and from 530 to 180 kDa in terms of molar mass (mass average; Mw), have been tested as matrix polymers in wood polymer composites (WPCs) with a wood content of 40%. To check for possible molecular weight controlled interactions between matrix and additives, five different maleic anhydride grafted PP (MA-PPs) coupling agents (CAs) have been included in the screening as well. Flexural properties, impact strength, and water absorption of the resulting composites served as responses. In addition, crystallinities, surface contact angles (on solid specimens), and rheological properties of the melt were measured for several compounds. The most important outcome of the study is that matrix polymer properties, as influenced by molar mass, are largely reflected in the resulting WPCs. Surprisingly, water absorption of the composites increases with matrix MFR, a phenomenon as yet not published for PP-based compounds. Furthermore, dynamic rheometry results indicate that the interaction of wood particles with PP melts is dependent on polymer and coupling agent Mw. © 2013 Society of Plastics Engineers Copyright © 2013 Society of Plastics Engineers.

Sobczak L.,Competence Center for Wood Composites and Wood Chemistry Wood us | Lang R.W.,Johannes Kepler University | Reif M.,Competence Center for Wood Composites and Wood Chemistry Wood us | Haider A.,Competence Center for Wood Composites and Wood Chemistry Wood us
Journal of Applied Polymer Science | Year: 2013

Polypropylene (PP)-based wood polymer composites with 40 and 60 m % wood content, respectively, have been prepared, employing two different wood types and 0.0-20.0% (based on wood content) of a maleated polypropylene (MA-PP) coupling agent (CA). The main objective of this research was to find out if the optimum CA content is dependent on wood filler particle size. Tensile and flexural properties, as well as impact strength, heat deflection temperature, and water absorption served as indicator properties for the CA influence. For all properties, there is an optimum or the onset of a plateau occurring between 8.0 and 13.0 m % MA-PP content. Flexural properties were determined after 28 days of water submersion as well, for both wet and redried specimens, revealing that the mechanical properties can be restored to a large extent in sufficiently coupled compounds. A dependence of the MA-PP content optimum on particle size was not detected. Copyright © 2013 Wiley Periodicals, Inc.

Discover hidden collaborations