Study On The Effect Of Preparation Methods On The Properties Of Sisal Fiber/PLA Composites

As the reinforced material, the natural fiber has been the first choice of manufacturingthe biodegradable composites. The structure and properties will change during processing,which results the mechanical and biodegradable properties of composites change. Thus, thepreparation method is a key role to the properties of composites.In this paper, three preparation methods which are different on shearing and thermalhistory includes: open mill mixing-platen, internal mixer mixing-platen, open millmixing-sheet extruding by singe screw extruder-lamination (open mill and extrusion mixing).Through analyzing the changes of PLA and alkali-treatment sisal fibers (ASF) duringprocessing, the effect of different preparation methods on the mechanical and biodegradableproperties of ASF/PLA are studied combined with the fibers filling rate.The changes of chain structure, molecular weight and distribution, crystallinity of PLAafter processing are studied by FTIR, GPC, and DSC. It’s found that: the thermo-oxidativedegradation leading to the cleavage on the chain during processing, which causes theincreasing of the content of carboxyl-terminated, the Mw/Mn, and the reducing of Mw andMn. The crystallinity of PLA obtained from the three preparation methods is36.44%,35.42%and38.56%respectively.The fibers surface morphology, length and its distribution, diameter are studied by SEMand Stereo microscope respectively. It’s found that: the fibers damage is not significantlydifferent when the fibers filling rate is low. With the increasing of filling rate, the changes offibers damage and fracture mode are different. In the three preparation methods, the lengthinterval is0.4~7.9mm,1~8.1mm,0.1~4.1mm respectively. The fibers diameter is not differentin the first two preparation methods, but both greater than open mill and extrusion mixing.The effects of preparation methods on mechanical properties are different. Conclusively,when the fibers filling rate is same, the tensile strength and impact strength of composites arebest in open mill mixing; the flexural strength is best in internal mixer mixing; the tensilemodulus is best in open mill and extrusion mixing. When the fibers filling rate is less than 30%, the flexural modulus of composites in open mill and extrusion mixing is best, and ininternal mixer mixing is best when the filling rate is greater than30%. With the increasing offilling rate, the tensile strength, flexural strength and impact strength first increase and thendecrease, but the flexural strength in open mill and extrusio n mixing decrease; the tensilemodulus and flexural modulus increase stably.The biodegradable performances of ASF/PLA composites are studied by vitro enzymaticdegradation and compost soil burial experiment. The results showed that: the fibers andmatrix both degraded; the intensity of surface erosion in descending order is open mill andextrusion mixing, open mill mixing,internal mixer mixing. With the increasing of filling rate,the weight loss rate increase. The surface and microscope morphology changes are similar inthe two experiments, but the cycle of latter is long and the results are not accurate enough.