Chuanshuang Hu

Isolation of cellulose nanocrystals from medium density fiberboards

Cellulose fibers have been successfully isolated from medium density fiberboards (MDFs) by sodium chlorite oxidation-potassium hydroxide (NaClO2-KOH) leaching process, at 37.6% yield, comparable to the 39.3% and 37.3% cellulose fibers from eucalyptus and eucalyptus with 12% cured urea-formaldehyde (UF) resin, respectively. At the same sulfuric acid hydrolysis conditions (65% H2SO4, 60°C and 30min), MDF cellulose nanocrystals (CNCs) were produced at 27.5% yield, similar to 27.4% of CNC yield from eucalyptus with UF resin, but less than 31.2% yield from eucalyptus. MDF CNCs were slightly thicker in lateral dimension (16.8±8.6nm), less crystalline (59% CrI), and surface esterificated (0.045mmol/g sulfate/CNC) than eucalyptus CNCs (11.6±3.9nm, 75% CrI, 0.060mmol/g) and CNCs from eucalyptus with UF resin (14.9±9.1nm, 65% CrI, 0.046mmol/g). All CNCs were free of UF resin and thermal stable. The residual resin in cellulose pulps hydrolyzed completely during the sulfuric acid treatment and contributed to the unique properties of CNCs. Therefore, CNCs derived from MDF are comparable to CNC from wood and promising for expanded applications.

Cellulose I and II nanocrystals produced by sulfuric acid hydrolysis of Tetra pak cellulose I

Polymorphism is an important factor associated with the cellulose nanomaterial properties. In this study, cellulose fibers (CFs) were efficiently isolated from waste Tetra pak packages, and cellulose I and II nanocrystals were produced by treatment of CFs with 64% sulfuric acid and controlling the reaction time from 15 to 30 min. Cellulose I (CI) was partially converted to cellulose II (CII) within 15 min and the resulting cellulose nanocrystal product (i.e. CNC15) contained 93.2% CII. Further extending the hydrolysis time decreased the CII content of CNC20 to 25.5% and CNC30 was completely CI without CII. CNC15 (285.1 ± 120.7 nm long, 50.6 ± 16.5 nm wide, 0.64 at% sulfur) was much thicker, slightly longer, less thermal stable and contained more sulfate groups than CNC30 (207.2 ± 77.8 nm long, 23.2 ± 7.8 nm wide, 0.34 at% sulfur). CNCs with controllable allomorph may have potentially diverse applications.

Damage detection of wood beams using the differences in local modal flexibility

Local damage such as knots, decay, and cracks can result in a reduction of service life due to mechanical and environmental loadings. In wood construction, it is very important to evaluate the weakest location and to detect damage at the earliest possible stage to avoid future catastrophic failure. In this study, modal testing was carried out on wood beams to generate the first two mode shapes. A novel statistical algorithm was proposed to extract the damage indicator by computing the local modal flexibility before and after damage in timbers. Different damage severities, damage locations, and damage counts were simulated by removing mass from intact beams to verify the algorithm. The results indicated that the proposed statistical algorithm is effective and suitable for the damage scenarios considered. The algorithm was reliable for detecting and locating local damage under different damage scenarios. The peak values of the damage indicators computed from the first two mode shapes were sensitive to different damage severities and locations. This approach was also reliable for detecting multiple defects.