Effect Of Thermo-treatment On Physical, Mechanical Properties And Durability Of Reconstituted Bamboo Lumber

As a bamboo-based composite made by bamboo bundles, reconstituted bamboo lumber is an economic wood substitution and can fully use the small-diameter bamboo. With the beautiful texture, color and excellent physical and mechanical properties,reconstituted bamboo lumber products have been widely used as furniture and decoration materials. However, the demand for outdoor reconstituted bamboo lumber was increasing with the breakthrough of reconstituted bamboo lumber manufacturing technology, and thus the lumber's durability has become a research focus. Carrying out systemic research on the aging properties, decay resistance and mould inhibition properties of reconstituted bamboo lumber will provide specifications for standards making and products developments, and thus promote its outdoor application and increase its added value.In this paper, Neosinocalamus affinis bundles thermo-treated with different temperature )160℃,180℃and 200℃)and duration (2h,3h and 4h) were chosen as basic raw materials, and then reconstitued with phenol-formaldehyde adhesive and hot pressing process. The effect of thermo-treatment on physical, mechanical properties and chemical components of reconstituted bamboo lumber were studied. The properties of thermo-treated reconstituted bamboo lumber after artificial weathering test, outdoor aging test, accelerated aging test and mould and decay test were analysed, the relationship between of artificial accelerated test and outdoor aging test were also discussed. The main results were summarized as follows,(1)As the increase of the thermo-treated temperature and duration, the MOR and horizontal shear strength decreased obviously with the max decreasing value of 49% and 30% compared with the untreated specimens, respectively. Thermo-treated temperature did more effect on the mechanical properties than thermo-treated duration. The MOE didn't change much after thermo-treatment. The 24 h thickness swelling decreased 30% after 200℃thermo-treatment. The surface color turned from light to dark as the increasing thermo-treated temperature and time.The chemical analysis of thermo-treated bamboo showed that theα-cellulose content decline and positively correlated with the MOR as the thermo-treated temperature increased, and the lignin content was slightly increased. (2) Xenon-arc lamp irradiation + water spray, xenon-arc lamp irradiation and low temperature xenon-arc lamp irradiation methods were applied in the durability testing of reconstituted bamboo lumber. The effect of these three methods on surface color was xenon-arc lamp irradiation + spray> xenon-arc lamp irradiation > low temperature xenon-arc lamp irradiation. Besides xenon irradiation, the existing of temperature and moisture would also affect the surface color. Thermo-treatment and surface coating would help improve the surface color stability of reconstituted bamboo lumber.FT-IR analysis of reconstituted bamboo lumber after xenon-arc lamp irradiation showed that the absorption bands related to lignin changed obviously, which represented lignin in bamboo was most vulnerable to photodegradation.(3)After 9 months'outdoor aging test, the change of total colorΔE*ab was quite similar to that after xenon-arc lamp irradiation + spray. The xenon-arc lamp irradiation + spray test was quite fit with color changes of the outdoor aging test.Thickness swelling and water absorption changed differently as the climate conditions and highly correlated with the air humidity and temperature at 0.01 and 0.05 level with the multi-regression analysis, respectively. The MOR, MOE and horizontal shear strength of reconstituted bamboo lumber behaved excellent mechanical stability after outdoor aging test with small decrease.(4)As the increase of thermo-treated temperature, the thickness swelling decreased of the three accelerated aging test, including the six-cycle accelerated aging, immersion and wet-dry cycle tests. Similar to the outdoor aging test, there was no obvious change in mechanical properties of reconstituted bamboo lumber after the six-cycle accelerated aging test and the maximum thickness swelling after six-cycle accelerated aging test was quite close to that of the outdoor aging test. So the six-cycle accelerated aging test could be used to simulate the mechanical and thickness swelling changes of the outdoor aging test.(5)Reconstituted bamboo lumber was a good decay resistance material with decay resistance reaching gradeⅠ. As the increase of thermo-treated temperature and duration, the decay resistance ability was improved indicating by the decreasing weight loss of reconstituted bamboo lumber. The mould inhibition of reconstituted bamboo lumber was also increased with the thermo-treated temperature and duration increased, but the destroy values were still above 3.5. The mould inhibition of anti-mould treated and coated reconstituted bamboo lumber was increased, but not obviously. There was no prevent effectiveness of blue stain fungi on reconstituted bamboo lumber, no matter how it was treated, however, no blue stain fungi was found inside of the reconstituted bamboo lumber.