Influences of surface chemical composition on the mechanical properties of pulp as investigated by SEM, XPS and multivariate data analysis

Abstract

Os efeitos da composição química total e da superfície nas propriedades mecânicas (MP) da polpa kraft de eucalipto foram investigados usando cromatografia líquida (HPLC), microscopia eletrônica de varredura (SEM), espectroscopia de fotoelétrons de raio X (XPS) e análise de components principais (PCA). Imagens em SEM das regiões fraturadas durante testes de rasgo (TrID), tração (TsID) e estouro (BuID) em amostras refinadas mostraram deformação das fibras e uma baixa proporção de fibras quebradas, indicando rupturas inter-fibras no arranjo fibroso. TrID de amostras não refinadas foi afetado pela cobertura surperficial de lignina (SLig), enquanto que TSID e BuID foram afetados pela cobertura superficial de extrativos (SExt) e carbohidratos (SCar). Após o refino, TrID foi afetado por ácidos urônicos presentes na xilana e a influência da composição química total foi muito mais pronunciada. Nossos resultados indicaram que as ligações fibra-fibra foram o fator limite para as MP mais do que a resistência das fibras individuais. Uma estratégia combinando modificação da superfície das fibras com a preservação de polisacarídeos durante a polpação foi sugerida para aprimorar as MP desse material.The effects of bulk and surface chemical composition on the mechanical properties (MP) of eucalyptus kraft pulp were investigated using Liquid Chromatography (HPLC), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Principal Component Analysis (PCA). SEM images of fractured regions during tear (TrID), tensile (TsID) and burst (BuID) tests of refined pulps showed fibre deformation and low proportion of broken fibres, indicating an interfibre failure in the sheet network. TrID of unrefined samples was affected by lignin surface coverage (SLig) while TsID and BuID were affected by surface coverage of extractives (SExt) and carbohydrates (SCar). After refining, TrID was affected by uronic acids (UA) in xylan and the influence of bulk composition was more pronounced. Our results also indicated that the fibre-tofibre bonding rather than the individual fibre strength was the limit factor for MP. A strategy combining surface modification and preservation of polysaccharides in pulping was suggested to improve the MP of this material.Keywords: eucalyptus, cellulosic fibre, surface composition, mechanical properties, XPS, PCA IntroductionSurface chemistry of pulp fibres has attracted remarkable research interest, especially in the latest years. The idea that surface characteristics play an important role in pulping, bleaching and papermaking processes was subject for many reported studies.1-3 Surface investigations are relatively complex due to intrinsic characteristics of wood materials such as component location in fibre wall and modifications introduced by the different processes. Generally spectroscopic techniques using high vacuum interfaces are applied to achieve surface sensitivity of a few nanometres and X-ray Photoelectron Spectroscopy (XPS/ESCA) has been proposed to determine the surface composition of c...

Effects of kraft pulping on the interfacial properties of Eucalyptus pulp fibres

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Influence of surface morphology of the kraft pulp fibers on the growth of the transcrystalline layer of polypropylene

“…In general, the surface sensitivity of the EDXA in energy levels of a kα X‐ray source is about 1–2 μm depending on the surface conditions of natural fibers, voltage setting, detector angle, detector type, and optimum collection time 17. Conversely, XPS, also known as electron spectroscopy for chemical analysis, is a surface analysis technique used to obtain oxygen/carbon (O/C) ratios on fiber surfaces with 3–10 nm in surface sensitivity 18–21. The XPS is often considered superior to EDXA when nano scale resolutions are desired, but can be disadvantageous when mean O/C ratios at the micrometer scale are needed.…”

Effects of site on fibre, kraft pulp and handsheet properties of Eucalyptus globulus

“…In recent years, new emerging technologies have allowed rapid and efficient characterisation of wood samples (e.g. Downes and Drew, 2007;Downes et al, 1997;Evans, 1994;Evans et al, 1995;Fardim and Duran, 2005;Muneri and Balodis, 1997;Schimleck et al, 2006). These new evaluation techniques are especially useful for measuring the large variation of wood properties within and among trees, clones, families, provenances, species and genera.…”