Study On Continuous Plasticiaing-molding Mechanism And Structural Properties Of Plant Fiber Filling Composites By Volume Elongational Deformation

Plant fiber filling composites are the novel sort of bio-compatible materials.While,the traditional shear rheology-based screw processing equipment has a poor ability on the plant fiber dispersion in the polymeric matrix.Moreover,the large shear force during processing will also lead to the breakdown and thermal-degradation of the plant fiber and consequently reduce the final performance of the composites.Meanwhile,owing to the low flow-ability of the plant fiber filling composites,it is difficult to be injected into the final product.Although the compression molding technique has low requirement in the material's flow-ability as well as a high automation,and the instability of the product's size also hinders its application.In this paper,the continuous plasticiaing-molding of plant fiber filling composites was proposed for the first time and the device was developed meanwhile.In which,the volume changes from large to small and then from small to large,during the plasticiaing and conveying process of composites which undergoes a periodic“compression-expansion”mixing process,then the preparation of plant fiber filling composites is based on the volume elongational rheology theory.The mathematical model was established according to the mold filling process and holding cooling process of compression molding for the theoretical derivation of flow distribution and temperature change which provides the basic theory for molding.A comparison of the properties of the Polylactic acid?PLA?/Bamboo fiber?BF?composites preparation through eccentric rotor extruder?ERE?and twin-screw extruder?TSE?has been made herein.In the morphological analyses,most of BF was well dispersed in the PLA matrix in samples fabricated under the elongation flow field which could consequently improve the mechanical properties of composites greatly.There was a more prefect?-form crystal at2?=16.5°and 19.0°corresponding to the diffraction peaks of?110??200??203?and a significant?-form crystal at approximately 2?=31.0°which was attributed to the promoting of elongation flow field.The T_5%,T_50%and T_max of composites in the shear flow were lower than that in the elongation flow with the addition of BF through the studying of thermal analysis;water absorption of composites was decided by the addition of BF and flow field,then,the BF was closely arranged and hinders the entry of water molecules in the elongation flow field.The effect of plant fiber loading and processing rotation speed on the morphological properties of plant fiber filling composites fabricated by ERE are also analyzed.Different dispersion effect are detected using plant fibers with various morphological.Among which the best loading of EWF and LF were both found to be around 30 wt.%.Which lead to a uniform dispersion in PP matrix as well as the best mechanical properties.On the other side,the best concentration of WSF was found to be around 20 wt%.The standing time and output of each plant fiber was tested to be the same.The ERE could generate elongation flow changed by different rotor speeds and the fiber dispersion in the PP matrix is different,the EWF could well disperse with 80 rpm.For LF,it can be well dispersed in the matrix with 40rpm,80rpm,120rpm.The PP/WSF composites could obtain the most excellent performance with the rotor speed80rpm.The results show that different plant fibers have a low influence on the thermal properties of the composites and indicates a relative-stable under the elongation flow generated by the ERE.The linear relation between standing time and output with the rotor speed suggests the conveying mechanism of ERE.The molding time,molding temperature and billet placement could affect the warping degree of product through the studying of the temperature distribution in the process of molding.It is obvious that the longer time,lower temperature and more reasonable billet could obtain the more uniformly temperature distribution and smaller warping degree,then the size stability of the product can be improved.The usage of multi-billet technique is found to improve the stability of the post-mold temperature and the size-stability of product.Sum up,a continuous plasticiaing-molding process based on ERE for plant fiber filling composites is proposed in this paper which could promote the application of environmentally friendly packaging materials.