Mechanistic study of microstructural deformation and stress in steam-exploded softwood

Muhammad Muzamal,E Kristofer Gamstedt,Anders Rasmuson

doi:10.1007/s00226-017-0896-7

Muhammad Muzamal, E Kristofer Gamstedt + Show 1 more

Open Access

https://doi.org/10.1007/s00226-017-0896-7

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Abstract

Steam explosion pretreatment results in the formation of microcracks in the cell walls of wood. In the present study, steam explosion experiments were performed and structural changes in Norway spruce were identified using scanning electron microscopy. The cellular structure of the softwood spruce was simulated using the finite element method, and the effects of pressure generated during the steam explosion pretreatment on the deformation of the cells were investigated. The simulated model included earlywood, latewood, and ray cells. The effects of bordered and cross-field pits on the stresses in the cell wall were studied as well. Many similarities were observed between the microcracks in the steam-exploded wood and the high-stress regions predicted by the model. The experimental and simulation results showed that the radial cell walls in the earlywood cells experienced major deformation. The presence of the pits created stress localization and facilitated the formation of microcracks in the cell walls.

Highlights

Wood material is a widely available low-cost renewable resource from which many useful chemicals and biofuels can be derived (Goldstein 1981; Claassen et al 1999)
This study has examined the effects of internal pressure created during Steam explosion (SE) pretreatment on a bundle of cells composed of earlywood and latewood cells
Modelling the process revealed the areas in the cellular structure of wood which are prone to break as a result of the internal pressure caused by the steam explosion

Summary

Introduction

Wood material is a widely available low-cost renewable resource from which many useful chemicals and biofuels can be derived (Goldstein 1981; Claassen et al 1999). De Magistris and Salmen (2008) have modelled a bundle of cells with a square shape to study the wood cell deformation transverse to the fibre axis under compression and combined shear and compression load These authors found out that the most important factor governing the deformation of fibres is the cell structure independently of material constants and number of cell wall layers used in the FEM models. The authors found out increasing values of cell angles cause decreasing stress levels at the same deformation In both studies, good qualitative agreement between experiments and models was observed. A number of experimental studies on SE pretreatment demonstrate the structural changes that take place in wood cells because of explosive pressure release (Tanahashi et al 1982; Toussaint et al 1991; Zhang and Cai 2006). The simulation results have been qualitatively compared with experimentally obtained steam-exploded wood

Experimental procedures

Results and discussion

Conclusion