Microstructure Transformation In Palm-Fiber Cell Wall And Its Influence On the Fiber's Mechanical Properties During Alkali Treatment

In this study, we examined the microstructure transformation of palm fiber and the influence of this transformation on the fiber mechanical properties during alkali treatment. The fibers were treated with different concentrations of NaOH to study the change rules of the microstructure and the tensile properties. FT-IR microspectroscopic imaging and confocal laser scanning microscopy were adopted to observe microstructure transformation during alkali treatment. Research results showed that the hemicellulose and lignin in the fiber cell wall were removed by alkali treatment, leading to a rearrangement of cellulose chains. The tensile properties palm fibers were significantly improved because of crystallinity alterations in the cell walls after alkali treatment. This study might provide a basis for palm fiber’s high-value utilization in the field of materials.

Effect of soil type on mean annual increment, wood anatomy and properties of 33-year-old Corymbia citriodora (Hook.), K. D. Hill, & L. A. S. Johnson

This study aimed to determine the effects of physical, chemical and water-holding capacity of Quartzarenic Neosol, Red Latosol and Red Nitosol on tree growth, physicomechanical properties and anatomical features of wood from 33-year-old C. citriodora plantations. More clayey soils with higher water availability, such as Red Latosol and Red Nitosol, increased the mean annual increment and heartwood percentage. In more sandy soils, such as Quartzarenic Neosol, density increased, but the size and diameter of fibers and vessels decreased, and both fiber cell wall thickness and frequency of vessels and rays increased. Wood shrinkage and mechanical properties did not differ between soils. We observed a gradual increase in the anatomical, physical and mechanical characteristics in the pith-bark direction. The uniformity index showed that Quartzarenic Neosol and Red Latosol soils produced more homogeneous woods. We concluded that soil texture and water availability influenced tree growth, anatomical properties and wood density.

Change in Micromechanical Behavior of Surface Densified Wood Cell Walls in Response to Superheated Steam Treatment

The combination of surface densification and superheated steam treatment is an effective method to improve the mechanical properties and dimensional stability of low-density wood. The objective of the current work is to evaluate the effects of superheated steam treatment on the micromechanical behavior of surface densified wood. The microstructure, chemical composition, cellulose crystalline structure, and micromechanical behavior of surface densified wood under different superheated steam pressures were investigated. Results indicated that both 0.1 MPa and 0.3 MPa superheated steam treatments increased the elastic modulus and hardness of fiber cell walls in surface densified wood. However, the average creep ratio and maximum creep compliance J(50) of surface densified wood under 0.3 MPa decreased by 41.59% and 6.76%, respectively, compared with untreated wood. The improvement of elastic modulus, hardness and creep resistance of surface densified wood treated with superheated steam was associated with the increase of relative crystallinity (CrI) and crystalline size. In addition, 0.3 MPa superheated steam treatment displayed a better effect on the enhancement of the elastic modulus, hardness, and creep resistance of the fiber cell wall than 0.1 MPa superheated steam treatment.

Optimizing Cellulose Microfibrillation With NaOH Pretreatments for Unbleached Eucalyptus Pulp

This study aimed to assess the effect of drying unbleached Eucalyptus cellulose fibers after the application of pretreatments in order to optimize the microfibrillation process, as well as to evaluate the efficiency of NaOH pretreatments in reducing energy consumption for production of microfibrillated cellulose (MFC). Pretreatments with 0 wt% (untreated), 5 wt% and 10 wt% NaOH were evaluated. The length and width of the fibers pretreated with NaOH decreased significantly, mainly with hasher pretreatments. The removal of hemicellulose from the fiber cell wall was an important factor concerning the degree of fibrillation of the fibers. Pretreating fibers with 5 wt% NaOH for 2 h increased the water retention value (WRV), in addition to presenting the lowest energy consumption for fibrillation, promoting energy savings of up to 48%. Pulps that were not dried after the NaOH pretreatments incurred in easier microfibrillation and lower energy consumption when comparing to the dried pulp, which shows the negative impact of drying on the fibers to obtain the MFC.

Influence of chemical pretreatments on plant fiber cell wall and their implications on the appearance of fiber dislocations

The cell wall of plant fibers may contain irregular regions called dislocations. This study evaluated the effect of chemical pretreatment as a mechanochemical dislocation initiator in unbleached and bleached Eucalyptus sp. fibers. Accordingly, bleached and unbleached pulps of eucalyptus were subjected to chemical pretreatments with sodium hydroxide at concentrations of 5% for 2 h, 10% for 1 h and 10% for 2 h or with hydrogen peroxide. The extent of dislocations was evaluated by polarized light microscopy. Based on the observation, an index of dislocations (ID) expressing their ratio of cell wall as per two-dimensional (2D) imaging and their angle relative to the longitudinal direction of the fiber were estimated. Chemical pretreatments increased the ID for bleached and unbleached fibers as well as increased the changes in the curl of bleached and unbleached fibers for chemical pretreatments. Chemical pretreatment extracted the hemicellulose of the fiber cell wall causing some fiber to curl, which in turn generated new dislocations and modifications in the dislocation angles which may be useful for improving the deconstruction process of the cellulose fibers.

Activation of ACS7 in Arabidopsis affects vascular development and demonstrates a link between ethylene synthesis and cambial activity

Ethylene is a gaseous hormone that affects many processes of plant growth and development. During vascular development, ethylene positively regulates cambial cell division in parallel with tracheary element differentiation inhibitory factor (TDIF) peptide signaling. In this study, we identified an ethylene overproducing mutant, acs7-d, exhibiting enhanced cambial activity and reduced wall development in fiber cells. Using genetic analysis, we found that ethylene signaling is necessary for the phenotypes of enhanced cambial cell division as well as defects in stem elongation and fiber cell wall development. Further, the cambial cell proliferation phenotype of acs7-d depends on WOX4, indicating that the two parallel pathways, ethylene and TDIF signaling, converge at WOX4 in regulating cambium activity. Gene expression analysis showed that ethylene impedes fiber cell wall biosynthesis through a conserved hierarchical transcriptional regulation. These results advance our understanding of the molecular mechanisms of ethylene in regulating vascular meristem activity.

The shear and compressive yield stress of fibrillated acacia pulp fiber suspensions

The degree of interactions between fibers and the tendency of fibers to form flocs play an important role in effective unit operation in pulp and paper industry. Mechanical treatments may damage the structure of the fiber cell wall and geometrical properties, and ultimately change the fiber-fiber interactions. In this study, the gel crowding number, compressive and shear yield stress of fibrillated acacia pulps were investigated, and the results showed that the gel crowding number of the refined pulp samples ranged from 8.7 to 10.7, which were much lower than that of un-refined pulps. As the concentration increased, both the compressive yield stress {P_{y}} and shear yield stress {\tau _{y}} of all suspensions increased accordingly, and the yield stress was found to depend on a power law of the crowding number. Moreover, the values of {\tau _{y}}/{P_{y}} were also examined and the variation of {\tau _{y}}/{P_{y}} became largely dependent on the fiber morphology and mass concentration.

Mechanical properties of the fiber cell wall in Bambusa pervariabilis bamboo and analyses of their influencing factors

The cell wall mechanical properties are an important indicator for evaluating the overall mechanical properties of natural bamboo fibers. Using the nanoindentation technique, the variation of the mechanical properties of the fiber cell wall of Bambusa pervariabilis culms with different ages and different positions (both radial and longitudinal) was studied. Moreover, x-ray diffraction (XRD) was employed to measure the microfibril angle (MFA), and the correlation between the MFA and the mechanical properties of the fiber cell wall. The results showed that there was a remarkable difference in the fiber cell wall mechanical properties at different ages and at different radial and longitudinal positions. However, at different ages and at different positions, the absolute value of variation of MFA was less than 1° and was very minor. Furthermore, there was no significant correlation between the fiber cell wall mechanics and MFA, indicating that the mechanical property of the fiber cell walls might be synergistically affected by many factors.

Probing and visualizing the heterogeneity of fiber cell wall deconstruction in sugar maple (Acer saccharum) during liquid hot water pretreatment

The S2 layer was differentiated into heavy-damaged region with more polysaccharides removed and relatively intact light-damaged region after LHW pretreatment.