| Rape is a crucial economic crop in Hubei province, but, rape stalks were usually discarded and burned as agricultural waste. For avoiding resource waste and environmental pollution, preparation of wood plastic composite (WPC) using rape stalks and high density polyethylene (HDPE) were studied in this project. In order to study approaches that improve the compatibility between fibre and plastic more directly, the dominant fibrous ingredient of rape stalks (rape stalk rough fibre, RSRF) was prepared and used as the modifying object prior to further modification. The surface of RSRF was modified by combination of physical ultrasonic treatment and chemical esterification, and the modified RSRF was characterized on its surface performance, reactivity, crystallinity and thermal behavior. Finally, WPC sheet consisting of esterified RSRF and HDPE was prepared by die pressing method and its mechanical properties and water absorption property were measured. The main conclusions were as follows:1. The primary cuticula of rape stalks is compact and slippery, which has a weak medium layer containing fat and wax, and the bulk density was 0.3068g/cm~3. The main components of rape stalk (cellulose, hemicellulose and lignin) approach to the corn stalk and reed which are members of graminaceous plants and poplars which belongs to broadleaf. The ash content and extractions of rape stalks are close to that of corn stalk and reed while more than poplar's.2. The conditions for microwave esterification of RSRF were optimized through orthogonal tests (using 1g RSRF for each test). The highest esterification degree can be achieved using 6mL of acetic anhydride for esterification under power of 320W for 100s following pretreatment of microwave activation for 6min under power of 400W. Cellulose and lignin were extracted from RSRF and esterified, respectively. Esterification degree determination indicated a stronger esterification activity of cellulose than lignin. Fourier transform infrared spectrum (FTIR) showed sharp and specific ester band in either cellulose or in lignin esterified products. Because hydroxyl groups of cellulose, hemicellulose and lignin are able to react with acetic anhydride separately, esterification of RSRF should occur upon the three components simultaneously. 3. Factors of ultrasonic treatment time, amplitude, consistency and container capacity that influencing RSRF on aspects of microscopical shape, amount of total sacchride, water retention value, dye absorption rate and reaction activity were studied. The amplitude was the most significant factor that influencing the token parameters. When it was higher than 70%, the hemicellulose was broken up, fibre beams were torn diversely and the compact RSRF were disassembled into filaments. The token parameters (microscopical shape, amount of total saccharide, water retention value, dye absorption rate and reaction activity) were significantly increased during ultrasonic treatment from 0min to 10min, while their increment extent decreased from 10min to 30min. It is notable that a short term (within 10min) of ultrasonic treatment creates adequate specific surface area and reaction activity of RSRF. In view of economy and cavitation, consistency of 2% was more practical. The differences caused by containers capacity, ranging from 50mL to 500mL, were unconspicuous. Ultrasonic treatment and esterification are both able to decrease the crystallinity of RSRF. The crystalline peak in X-ray diffraction (XRD) transited from sharp peak to diffusing broad kurtosis. RSRF, ultrasonic treated RSRF and esterfied RSRF reduced their crystal size, N-O'KI and crystallinity in turn. These results indicated both ultrasonic treatment and esterification can break the crystal structure of RSRF. Thermal behavior of RSRF was not affected by ultrasonic treatment, but it remarkably changed in the esterified RSRF. The Differential Scanning Calorimeters (DSC) curves revealed the maximal thermal decomposition peak of cellulose and lignin in RSRF were disappeared, which reflected characters of RSRF were modified through esterification. Accordingly, the thermal stability of the esterified RSRF was also enhanced.4. The mechanical properties of WPC enhanced along with the improvement of esterified degree. The effect of ultrasonic treatment time on mechanical properties showed a time-dependent process, which was drastically enhanced in 0min～10min while plateaued in 10min～30min. Mechanical properties of WPC were also improved accompanied with the raised amplitude. This demonstrated that the surface corrosion of RSRF caused by ultrasonic treatment didn't influence the mechanical properties and it made the esterification more uniform contrarily. Well mechanical properties can be obtained using a consistency of 2%～3% and it was not evidently affected by various consistencies. After esterified, the shape of RSRF became ambiguous on the surface of WPC. Good compatibility at edges between RSRF and HDPE indicated components flowing and resulting homodisperse. Both the esterified RSRF and WPC sheet showed strong hydrophobicity which was increased following the improved esterified degree.
|
PDF Full Text Request