Application of The Lifshitz-van Der Waals Acid-base Approach To Determine Wood Surface Tension Components

Improvements are being made in the fundamental descriptions of surface thermodynamics, and it is important to apply these new concepts to wood. The purpose of this paper is to determine wood surface tension components using the Lifshitz-van der Waals/acid-base approach. Zisman plot, geometric-mean, and harmonic-mean wood surface tension determinations are also made for comparative purposes. Lifshitz-van der Waal forces appear to account for the majority of wood surface tension, and the acid-base character comes primarily from the electron donating γ-sites. The contribution of γ-sites on the wood surface to fundamental wood-adhesive interactions may have considerable implications in the gluing and finishing technology of wood, and it deserves further study. The Lifshitz-van der Waals/acid-base approach provides for greater accuracy in calculating wood surface tension components than the geometric-mean and harmonic-mean equations because it is based on the contribution of contact angles from five liquids versus two liquids. In some instances, the critical surface tension of wood obtained using Zisman plots compares favorably with the total surface tension obtained by the Lifshitz-van der Waals/acid-base approach

HYDROGEN BONDING IN WOOD-BASED MATERIALS: AN UPDATE

The contribution of hydrogen bonding to wood science and technology has been well recognized over the past century. The hydrogen bond is an important chemical characteristic contributing to wood-based material behavior and it also provides an important contribution to processing features of wood. However, the current understanding of hydrogen bond strength as a contributor to wood-based material behavior has not been updated in the wood literature. Wood-based material literature typically report hydrogen bond strengths ranging from 12.6 to 25.2 kJ/mol (3 to 6 kcal/mol) while newer data from the general chemistry field report hydrogen bond strengths up to 189 kJ/mol (45 kcal/mol), which are characteristic of covalent bond strength. In light of these new data regarding hydrogen bond strengths, it provides impetus to discuss the new understanding of hydrogen bond strength relative to wood-based material behavior. Recent developments in nanotechnology of renewable materials leading to the production and applications of cellulose nanomaterials with much higher surface areas and hydrogen bonding capacity also mandate revisiting our knowledge of the hydrogen bonding mechanism and strength

Changing teacher educational contexts: Global discourses in teacher education and its effect on teacher education in national contexts

Teacher education has gathered interest globally and nationally among teachers, educators, researchers and policy makers. Madalinska-Michalak, O ’Doherty and Assuno Flores (2018) observe that regional/ national, social, economic, political and historical factors impact upon teacher education and ‘it is also impacted by global problems and tendencies’ (pp. 567). This paper builds on these debates and examines the effects of global discourses of teacher education in the national contexts of developed and developing countries, for example, Guyana, Japan, South Africa, United States of America (USA) and the United Kingdom (UK). This includes consideration of teacher education and training before and during the current global Covid-19 pandemic (UNESCO, 2020). The paper concludes that teacher education continues to be under scrutiny due to global and national expectations, the demand of and how they are positioned in preparing teachers for the 21st century. Notwithstanding, as globalisation becomes more integrated in societies globally teacher education curricula not only has to retain its emphasis on standards, but equally its agility to ensure that the needs of all learners are met

\u3ci\u3eHeligmosomoides thomomyos\u3c/i\u3e sp. n. (Nematoda: Heligmosomidae) from Pocket Gophers, \u3c/i\u3eThomomys\u3c/i\u3e spp. (Rodentia: Geomyidae), in Oregon and California

The nematode Heligmosomoides thomomyos sp. n. is described from the small intestine of Thomomys bulbivorus and T. bottae. This is the first report of Heligmosomoides from rodents of the family Geomyidae. Nematodes of the genus Heligmosomoides Hall, 1916 occur most commonly in arvicolid rodents. Of the 26 known species of the genus, 11 have been recorded from Nearctic rodents (Rausch and Rausch, 1973). In North America, Heligmosomoides spp. have been recorded not only from voles, but also from cricetids and murids. Heligmosomoides spp. characteristically inhabit the small intestine or cecum of their host, where they usually are found tightly coiled around the intestinal or cecal villi (Durette-Desset, 1971). Nematodes representing an undescribed species of Heligmosomoides were found by us in the small intestine of pocket gophers (Geomyidae) of two species, Thomomys bulbivorus (Richardson), from Benton County, Oregon, and T. bottae (Eydoux and Gervais), from Humboldt County, California (collected respectively by S.L.G. and D.P.J.). Rodents of the genus Thomomys have an extensive geographic range in central and western North America. Thomomys bulbivorus is endemic to the Willamette Valley of Oregon, and T. bottae occurs from southwestern Oregon southward to Arizona and northern Mexico (Hall and Kelson, 1959; Ingles, 1965). It is the purpose of the present paper to describe this nematode, which is the first species of Heligmosomoides to be recorded from rodents of the family Geomyidae

Enhancing the Fuel Value of Wood Pellets with the Addition of Lignin

Because of the increased cost of petroleum-based energy production, there is renewed interest in the use of wood for energy. In particular, residential heating using wood pellets has experienced a large increase during the last decade. Manufacturers of wood pellets are interested in producing high-quality, high fuel-value pellets. In this study, lignin was explored as an additive to wood to enhance pellet fuel value. Two types of lignin were examined in the production of wood pellets, Kraft black liquor and Indulin AT (IAT). Lignin was added to a softwood furnish and pellets were prepared on a commercial California Pellet Mill. The pellets were analyzed for fuel value, moisture content, and quality. Those prepared with IAT produced better quality pellets and had a higher fuel value than with Kraft black liquor. The Kraft black liquor pellets were soft and spongy and easily fell apart. A cost analysis indicates that lignin preparation will have a major impact on the feasibility of adding lignin to wood pellets to enhance fuel value

Mechanical Properties of Cellulose Nanofibril-Filled Polypropylene Composites

Cellulose nanofiber (CNF), microfibrillated cellulose (MFC), and microcrystalline cellulose (MCC) filled-polypropylene (PP) composite samples were manufactured using a melt mixing technique. Mechanical testing was conducted to investigate tensile and flexural properties of the composites at different filler loading levels. Test results showed that in the case of cellulose nanofibril fillers, the composites sustained considerable tensile strength up to 10% (w/w) filler loading whereas the tensile strength of the MCC-filled composites decreased continuously. Moreover, tensile modulus increased as filler loading increased for all cellulose fillers. CNF and MCC-filled composites demonstrate plastic deformation and longer elongation at break than MFC-filled composites while MFC-filled composites exhibited a quasi-brittle behavior under tensile deformation. Flexural strength of cellulose nanofibril-filled composites decreased slightly as a function of filler loading up to 6% (w/w) and increased beyond 6% (w/w). The 10% (w/w) cellulose nanofibril-filled composite samples exhibited sustained flexural strength as compared with neat PP. The trend of increased flexural modulus of elasticity behavior was identical to the tensile modulus of elasticity behavior

An Evaluation of Analysis Methods to Eliminate the Effect of Density Variation in Property Comparisons of Wood Composites

The objective of this research was to evaluate commonly used data analysis methods in property comparisons of wood composites to eliminate the effect of the density variation among board test specimens and to suggest a more reasonable and robust method. The methods reviewed included average, specific strength, and analysis of covariance. The indicator variable method was also applied to the property comparison and compared to the other methods. The modulus of rupture of wood fiber/polymer fluff composites manufactured with different material combinations and press temperatures was tested in the experiment for evaluation of the different analysis methods. The results of this study indicated that the statistical analysis method employed was very important in the study of the physical and mechanical properties of wood composites. The specific strength method is limited to the analysis of strength comparison for the high density composites. The analysis of covariance can be applied to all the property comparisons for either high or low density composites in eliminating the density variation effect. However, error exists in the property comparison using the analysis of covariance method when the slopes of the regression lines of property vs. specific gravity (SG) are different for the different composites being tested. The indicator variable method is shown to be more reliable than the specific strength and analysis of covariance methods because it compares the linear regression lines of property vs. SG by testing both the intercept and slope based on the data in the whole specific gravity range of test specimens

Surface Activation Treatment of Wood and Its Effect on the Gel Time of Phenol-Formaldehyde Resin

Surface activation treatment of wood using hydrogen peroxide, nitric acid, and sodium hydroxide was examined to assess its effect on the gel time of phenol-formaldehyde resin. Four wood species comprising both hardwoods and softwoods, two treatment levels, and two treatment conditions (activation and activation followed by drying) were examined in the study. The effect of surface activation on the gel time of phenol-formaldehyde resin varies for a particular surface activator according to treatment level and treatment condition. Surface activated treated wood decreases the gel time of phenol-formaldehyde resin with hydrogen peroxide treatment having the greatest effect followed by nitric acid and sodium hydroxide treatments

Dynamic Adhesive Wettability of Wood

Adhesive wettability of wood is usually evaluated by contact angle measurement. Because of liquid penetration and spreading on the wood surface, the contact angle changes as a function of time. In this study, a wetting model was developed to describe the dynamic contact angle process in which a parameter (K) can be used to quantify the adhesive penetration and spreading during the adhesive wetting process. By applying the wetting model, the adhesive wettability of sapwood and heartwood of southern pine and Douglas-fir was studied. Liquid wettability along and across the wood grain direction was also compared. Two resin systems, polymeric diphenylmethane diisocyanate (PMDI) and phenol-formaldehyde (PF), were evaluated. It was learned from this study that the wetting model could accurately describe the dynamic adhesive wetting process on wood surfaces. Through applying this model, it is shown that PMDI resin exhibited a better wettability on wood than PF resin. The adhesive is more easily wetted along the grain direction than across the grain direction. Species and drop location have no significant effect on the spreading and penetration rate (K-value). However, the interaction term between species and resin type shows a significant effect for the K-value. PMDI exhibits a greater K-value on the Douglas-fir surface, while PF resin shows a greater K-value on the southern pine surface. Heartwood shows a lower instantaneous contact angle than sapwood. Douglas-fir has a greater instantaneous contact angle than southern pine. The effect of species on the equilibrium contact angle is strongly dependent on the location of the drop on the wood surface. The equilibrium contact angle of Douglas-fir is smaller than that of southern pine for sapwood, but is greater for heartwood

Analiza kompozita od kopolimera stirena i anhidrida maleinske kiseline (SMA) punjenih pregrijanim drvom metodom konačnih elemenata

The computer aided three dimensional static analyses of the specimens was done by using the Finite Element Method (FEM) and obtained data was compared with actual test data. The aim of this study is to compare the deformation/stress analyses with FEM analysis results of styrene maleic anhydride (SMA) copolymer composites. The heat treated wood/SMA copolymer composites were produced from different loadings (from 10 to 30 wt. %) of heat treated and untreated eastern white pine wood flours (Pinus strobus L.). All formulations of wood flour/SMA copolymer composites were produced by melt compounding through injection molding. The deformation/stress results obtained from the experimental solutions are very close to the results obtained from the numerical solutions (SAP2000 V17). As a result, it can be said that it is beneficial to use the FEM in the engineering design approach after the data obtained by the experimental solutions as meaningful values after application of the FEM.Računalom potpomognuta trodimenzionalna statička analiza uzoraka provedena je metodom konačnih elemenata (FEM). Dobiveni su podatci uspoređeni sa stvarnim ispitnim podatcima. Cilj rada bio je usporediti analizu deformacija/naprezanja s rezultatima FEM analize kompozita od kopolimera stirena i anhidrida maleinske kiseline (SMA). Kompoziti od pregrijanog drva i SMA kopolimera bili su izrađeni s različitim udjelom (od 10 do 30 % težine) drvnog brašna od pregrijanoga i nepregrijanog drva američkog borovca (Pinus strobus L.). Sve formulacije kompozita od drvnog brašna i SMA kopolimera bile su izrađene injekcijskim prešanjem. Rezultati deformacija i naprezanja dobiveni eksperimentalno vrlo su slični rezultatima dobivenim računskim putem (SAP200 V17). Može se zaključiti da je analiza metodom konačnih elementa, kombinirana s eksperimentalno dobivenim podatcima, korisna u inženjerskom projektiranju