Kadivar Marzieh, Gauss Christian, Ghavami Khosrow, Savastano Holmer
Research Nucleus on Materials for Biosystems (NAP BioSMat), Department of Biosystems Engineering, University of São Paulo; Pirassununga, Sao Paolo 13635-900, Brazil.
School of Engineering, University of Waikato, Hamilton 3216, New Zealand.
Materials (Basel). 2020 Sep 29;13(19):4346. doi: 10.3390/ma13194346.
Densification processes are used to improve the mechanical and physical properties of lignocellulose materials by either collapsing the cell cavities or by filling up the pores, consequently reducing the void volume fraction. This paper focuses on an extensive review of bamboo densification process, which is achieved by compressing the material in the direction perpendicular to the fibers using mainly two different techniques: an open system, thermo-mechanical (TM), or a closed system, viscoelastic-thermal-compression (VTC). The main aim of bamboo densification is to decrease its heterogeneity, as well as to improve its mechanical and physical performance. In addition, densification may occur during the manufacturing of bamboo products in which hot-pressing processes are used to mold bamboo panels. There are over 1600 publications about bamboo, concentrated in the recent decade, mainly about engineered materials. Although several papers regarding bamboo and wood densification are available, very few studies have comprehensively investigated the densification process solely through compression of natural bamboo culms. According to the literature, applying a combination of compression of 6-12 MPa at temperatures between 120-170 °C for 8-20 min can produce materials with higher strength in comparison to the mechanical properties of natural bamboo. The majority of research on bamboo densification indicates that the modified material results in improved properties in terms of density, hardness, bending strength, stiffness, and durability. This paper provides a review that consolidates knowledge on the concept of bamboo culm densification, discusses the roles of parameters that control the process, ascertains the best practice, and finally determines gaps in this field of knowledge.
致密化工艺用于通过使细胞腔塌陷或填充孔隙来改善木质纤维素材料的机械和物理性能，从而降低空隙体积分数。本文重点对竹材致密化工艺进行了广泛综述，该工艺主要通过两种不同技术在垂直于纤维的方向上压缩材料来实现：一种是开放系统，即热机械（TM）工艺；另一种是封闭系统，即粘弹性热压缩（VTC）工艺。竹材致密化的主要目的是降低其不均匀性，并改善其机械和物理性能。此外，在竹制品制造过程中，当采用热压工艺来成型竹板时，也可能会发生致密化现象。关于竹子的出版物有1600多篇，集中在近十年，主要是关于工程材料方面的。虽然有几篇关于竹子和木材致密化的论文，但很少有研究仅通过对天然竹杆进行压缩来全面研究致密化过程。根据文献，在120 - 170°C的温度下施加6 - 12 MPa的压力并持续8 - 20分钟，与天然竹子的机械性能相比，可以生产出强度更高的材料。大多数关于竹材致密化的研究表明，改性后的材料在密度、硬度、抗弯强度、刚度和耐久性方面的性能得到了改善。本文提供了一篇综述，整合了关于竹杆致密化概念的知识，讨论了控制该过程的参数的作用，确定了最佳实践，并最终确定了该知识领域的空白。
