Partners and International Organizations
(English)
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AT, BG, CH, DE, ES, FI, FR, HU, IE, IL, IT, LV, NL, NO, PT, RO, SE, SI, UK
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Abstract
(English)
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The mechanical response of Softwood, Hardwood and bleached single pulp fibres was studied by in-situ SEM microindentation, microcompression and nanoindentation tests. Nanoindentation measurements on latewood cell wall cross-sections revealed no difference in hardness values between softwood pulp and hardwood pulp, but significantly lower values were found for bleached pulp fibres. Indentation modulus of 12 GPa was observed for unbleached softwood pulps, which is 25 % higher than unbleached hardwood pulps. After bleaching and drying processes, only negligible difference was observed in cell wall mechanical properties (hardness and indentation modulus) between hardwood and softwood pulps. Nanoindentation was also carried out on refined and unrefined single pulp fibres. Microindentation tests were performed to understand the deformation and fracture mechanics of pull fibre cell walls in transverse direction. For the first time, compression strength of single wood fibre was obtained by performing in-situ SEM compression of the secondary cell wall micropillars machined by using Focused Ion Beam technique (FIB). The secondary cell wall exhibited yield strength values of approximately 160 MPa and large scale plasticity. Finally, ex-situ uniaxial tensile tests of bleached pulp fibres revealed lower strength and modulus values for twisted and curled fibres compared to straightly aligned fibres. High resolution SEM imaging of the fracture surfaces revealed angular cleavage in the case of twisted and curled fibres.
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