Jin Hong Chemical Fiber

　　100-mesh and 120-mesh sieves for backup use; cellulose: prepared by the nitric acid-ethanol method; lignocellulose: prepared by the sodium hypochlorite method; lignin: prepared by the hypochlorite method.

 

　　14. The composite material was prepared by mixing plant fibers and their main components (cellulose, hemicellulose, and lignin) with PBS at a specific mass ratio using an SK-160 two-roll open-mill mixer (Shanghai Qicai Hydraulic Machinery Co., Ltd.) at 110°C for 10 minutes, followed by hot pressing to form standard specimens for tensile testing.

 

　　1.3 Performance Testing of Composite Materials 1.3.1 XRD Testing: The crystallinity of cellulose, hemicellulose, and the composite material was determined using an X-ray diffractometer (model D/Max-3c) manufactured by Rigaku Corporation of Japan.

 

　　2. Mechanical Property Testing: The mechanical properties of the composite material were tested using a XWW-10A universal tensile testing machine manufactured by Chengde Jinjian Testing Instrument Co., Ltd., in accordance with GB/T1040.3—2006. A tensile load was applied to the specimens at a rate of 5 mm/min until fracture occurred. Five parallel specimens were tested for each type of material, and the average value was taken.

 

　　1.3.3 Thermogravimetric Analysis: The analysis was performed using a TGA Q500 thermogravimetric analyzer (TA Instruments, USA). The test gas was nitrogen, and the temperature range was from 30°C to 600°C, with a heating rate of 10°C/min. The sample mass for the test was 4 mg. Contact Angle Measurement: A contact angle measuring instrument from Shanghai Solon Technology, model SL200A/B/D series, was used. Distilled water was employed as the testing medium. For the composite material samples, the following projects provided funding: the sub-project of the Ministry of Science and Technology’s “863” Program (2011AA100503); the industrialization and research cultivation project of the Shaanxi Provincial Department of Education (2010C01); and the National Key Laboratory of Polymer Materials Engineering. After adding plant fibers, the contact angles of the composites were lower than those of pure PBS. As the amount of plant fiber added increased, the contact angles of the composites continued to decrease. Among them, the contact angle of the bamboo fiber composite was the largest, while that of the wheat straw fiber composite was the smallest. The strong polarity of cellulose and hemicellulose, along with the phenolic hydroxyl groups in lignin molecules, endow plant fibers with high hydrophilicity. Therefore, when these fibers are blended with hydrophobic PBS, the composite material exhibits increased hydrophilicity due to the incorporation of hydrophilic plant fibers on one hand, and on the other hand, because of the poor compatibility between the fibers and the matrix, the interface between them is not tight, leading to an increase in surface and internal voids within the composite. Consequently, the overall hydrophilicity of the composite material is enhanced, and this enhancement becomes more pronounced with increasing plant fiber content. The differences in hydrophilicity among various plant fiber/PBS composites depend on the varying properties of the plant fibers themselves. As shown in Fig. 6(a) and Fig. 6(b), the cellulose and hemicellulose composites made from bamboo fibers, which have good crystallinity, exhibit relatively weaker hydrophilicity, whereas the cellulose and hemicellulose composites made from wheat fibers, which have poor crystallinity, display relatively stronger hydrophilicity. This is because materials with high crystallinity have fewer exposed hydroxyl groups in cellulose and hemicellulose, resulting in weaker water absorption and better compatibility with PBS resin. Consequently, the internal structure of these composites is tightly linked with few voids, leading to lower hydrophilicity. Figure 6(c) illustrates the hydrophilicity of different plant fiber-lignin/PBS composites. In general, the lignin composites made from wheat straw fibers show better hydrophilicity, while those made from bamboo fibers exhibit relatively weaker hydrophilicity. This difference is determined by the phenolic hydroxyl groups in lignin: the higher the content of phenolic hydroxyl groups, the stronger the hydrophilicity. In summary, the hydrophilicity of cellulose, hemicellulose, and lignin directly determines the hydrophilicity of the fibers themselves. The relatively higher hydrophobicity of bamboo fiber cellulose, hemicellulose, and lignin, combined with the large aspect ratio of bamboo fibers (bamboo fibers: 133; straw fibers: 114; wheat fibers: 102), results in tighter bonding within the bamboo fibers, thereby directly contributing to the relatively weaker hydrophilicity of the composite material.

 

　　3. Conclusion: As the particle size of plant fibers decreases, the mechanical properties of the composite material increase. As the amount of plant fiber added increases, the tensile strength of the composite material initially rises and then declines, while the elongation at break gradually decreases.

 

　　Among bamboo fiber, rice straw fiber, and wheat straw fiber, the bamboo fiber/PBS composite material exhibits the *best mechanical properties*, the *superior thermal stability*, and excellent hydrophobic performance; rice straw fiber ranks second, while wheat straw fiber performs the *worst*.

 

　　The performance differences of plant fiber/PBS composites depend on the variations in the properties of the plant fibers themselves. The higher the crystallinity of cellulose and hemicellulose, the better the performance of cellulose/hemicellulose/PBS composites—and consequently, the superior the performance of plant fiber/PBS composites.