Chemical and Physical Parameters of Different Modifications of Rape Straw (Brassica napus L.)

Abstract

Material alternatives to wood, such as rape straw, are needed for the production of composite materials. This study performed an analysis of rape straw as a composite material source for production. There were three types of rape straw particle modification: untreated particles as reference variant, boiling in water, and soaking in sodium hydroxide (NaOH) solution. The pH and calorific value were highest for the variant soaked in NaOH. The total elemental content and the elements on the rape straw surface varied between variants. The modification method chosen influenced the pH, calorific value, elemental composition, and contact angle. Keywords INTRODUCTIONRecently there has been an effort to develop new composite materials using alternative sources of raw materials. This trend is largely explained by population growth, which contributes directly to a limited supply of natural resources, as well as wood shortage in all wood processing industries (Galor and Weil 2000;Bektas et al. 2005;Seintsch 2011;Lauri et al. 2012). One alternative source of raw materials is post-harvest rapeseed crop residue (Mohanty et al. 2002;Dziurka et al. 2015). As a prospective raw material, rapeseed has many advantages, as it is available in large quantities and is not yet used in other products with high added value (Bečka et al. 2007;Dukarska et al. 2017). However, waxy and siliceous substances are present on the surface of winter rape stems, which prevents the formation of quality adhesion between particle and adhesive (Grigoriou 2000). This is the main disadvantage of particles from annual plants compared to wood particles. The chemical composition differs between internal and external areas of the stem because of cuticles and epicuticular waxes (Wiśniewska et al. 2003;Trischler, and Sandberg 2014). The surface has a strong impact on the water contact angle, which deteriorates the wetting of particles by adhesives, since adhesives used in particleboard production are mainly water-based (Wiśniewska et al. 2003). Therefore, it is necessary to pre-treat these particles from annual plants before the production of the composite material itself (Mahlberg et al. 1999;Cao et al. 2017). This modification can PEER-REVIEWED ARTICLE bioresources.com Částková et al. (2018). "Modified rape straw," BioResources 13(1), 104-114. 105 be done in various ways (Pelaez-Samaniego et al. 2013;Trischler and Sandberg 2014). Boiling in water is regarded favorably as a treatment due to its ease of implementation (Bekhta et al. 2013). An alternative is alkaline treatment, which breaks ester linkages between wax and lignocellulose, as well as dissolving wax and lignin (Binod et al. 2010;Wan et al. 2011). In this study, winter rape chips were modified by applying hydrothermal and chemical (soaking in sodium hydroxide) processes (Xie et al. 2010;Bekhta et al. 2013). It is assumed that the modification destroys the waxy, siliceous substances on the surface of the chips and consequently improves adhesion in the composite product. This study characterized the phys...

Changes in the Composition and Surface Properties of Torrefied Conifer Cones

“…Sample images with elemental distribution at the surface of scales are presented in Figure 2 . It was confirmed that carbon and oxygen have the highest percentage in lignocellulosic materials [ 62 ].…”

Influence of Lignocellulosic Waste Pre-Treatment on the Characteristics of Bond Rupture

“…Moreover, the failure is not areal as in the previous cases, but rather spatial. The presence of residual Ca crystals (marked by arrows) in the structure of the exposed mesh also has a significant but unknown effect [9]. Overall, after evaluating the observations of all variants, the bonding quality after alkaline treatment using epoxy polyester adhesive is the best.…”

“…Leaching in boiling water improves adhesion due to the partial removal of waxy substances from the particle surface [9]. The failure of the joint occurs at the adhesive and material interface (Figure 2a), but the cohesive failure in the material itself is also evident ( Figure 2b).…”

“…Surface erosion and irregularities can be observed ( Figure 3a). The adhesion is improved because of removal of the protective wax layer in combination with surface roughening [9]. The failure occurs both in the adhesive and in the bonded joint (to a small extent), as well as in the adherend (Figure 3b).…”

“…Low surface energy is caused by the presence of waxy substances, which must be removed in order to increase the surface energy of the bonded material and achieve better adhesion with the adhesive [8]. Various methods of material pre-treatment have been developed for this purpose [9,10]. It was shown that through increase of particle surface energy some of the pre-treatments improve the bonding between particle and surface.…”