The Characterization And Analysis Of Extensional Rheologic Properties Of Short Plant Fiber Filled Polymer Composites

In recent years, Wood Plastic Composite (WPC) is widely used in many areas. However, the composite, which is produced by adding wood powder or straw powder into polymer, behaves weak strength. Plant fiber/polymer composites, by contrast, behave high strength. Since fibers won’t break easily in elongation flow, it is useful to study extensional rheology of short plant fiber filled polymer composites.Since plant fiber/polymer composites behave weak melt strength, it is hard to measured extensional rheological properties of the composites using direct method. Contraction flow method, by contrast, is more suitable to evaluate the extensional rheological properties of plant fiber/polymer composites.In this study, a new set of capillary equipment was designed and used. It can be used to evaluate the shear and extensional rheoloic properties of composites at the same time. Thanks to its structure, the composites in the equipment, after experiment, can be taken out and sliced. The flow behaviors of the composites can be studied through microscope. The Gibson mold was used to evaluate extensional properties of the plant fiber filled polymer composites. It is found that the extensional rheological properties of HDPE, PCBF/HDPE, and SF/HDPE all obey the power-law model, and the m are all lower than1. It is to say that both neat HDPE and short plant fiber filled HDPE composites show strain-thinning behavior. Both extensional consistency index kE and extensional viscosity of the composites decrease firstly and then increase with fiber content increasing. When fiber content is lower than20wt%, kE of the pithecellobium clypearia fiber (PCBF) filled HDPE is much higher than sisal fiber (SF) filled HDPE, m is much lower. That is to say configuration of fibers has great influence on the rheologic properties when fiber content is low. But configuration of fibers has little influence on the rheologic properties of the composites when fiber content is high. The consistency index kE of PCBF/HDPE decreases slightly and then increases with fiber content increasing, and the minimum value arises at fiber content of5wt%. The kE of SF/HDPE decreases rapidly and then increases, and the minimum value arises at10wt%. The inlet angle has great effect on extensional rate. When inlet angle increases, the extensional rate increases firstly and then decreases. From the morphologies of the slices, it can be seen that the fibers distribute evenly when inlet angle is smaller than90degree. But the melt of metrix is rich in the inlet region and the component will differ from the center, which make astable flow occur.