Study On Surface Modification Of Natural Fibers And Polypropylene Composites

The natural fiber/thermoplastics composites are a kind of new natural greenenvironment-friendly materials, which are formed by wood fiber or otherlignocellulose fibers with various plastics in different combining ways. The limitedcompatibility between PP matrix and natural fibers is due to the fact that natural fiberis the polarity hydrophilic material while PP is the non-polarity hydrophobic material,therefore, surface modification of the fibers is an effective method to improve thecompatibility. We have determined the relative value of surface free energy and itspolar part before and after the fibers treated respectively with alkali and silane byself-made equipment, including different alkali treating time(24 hours, 48 hours, 72hours, 96 hours), different alkali treating concentration (10%, 15%, 20%, 25%)anddifferent silane treating time (24 hours, 48 hours, 72 hours, 96 hours). The resultsshowed that the polarity free energy of the natural fibers decreased after beingtreated with the best effects of alkali treating time at 72 hours, alkali concentration at20%, silane treating time at 72 hours. Furthermore, the FTIR spectra approved thatthe -OH decreased which standing for the polarity of fibers after they were treated.The effects of different treating conditions on the mechanical properties of thecomposites were also discussed. The results showed the best mechanical properties ofthe composites were realized when the fibers treated by 20% NaOH for 72 hours andby A151 for 72 hours were filled in. The tensile strength, elongation at break, flexuralstrength, impact strength, melt flowing rate, shore hardness and vicar softening temperature of composite were increased by 5%, 22%, 5%, 33%, 42%, 6%and 2% respectively. And the SEM illuminated the interfacial adhesion status andthe distributing of the fibers were improved after they were treated.In this paper, the effects on the properties of PP/ natural fibers composites filledwith untreated and treated fibers (rice husk flour, bagasse, hard wood flour andbamboo flour) were also studied. In this experiment, the properties of the compositesfilled with untreated fibers, alkali treated fibers and silane treated fibers were tested.With the increase of the content of fibers, the flexural strength and the shorehardness rose because fibers made the composites have more better rigid, waterabsorption capacity went up, the vicar softening temperature rose because theheat-durability of the composites was improved; the tensile strength, impact strengthand the elongation at break, the melt flowing rate decreased. The best properties ofcomposite could be obtained at 40 phr. The compatibility between fibers and PP wasimproved with the mechanical properties, water absorption capacity, the fluidity andthe heat-durability of the composites filled with treated fibers were improvedrespectively compared to the untreated natural fibers/pp composites.The properties of composites were optimized innovatively in view of thenatural surface performance. We worked out the values of the polar surface freeenergy of the fibers before and after being treated by using Washburn Osmoticmethod and Young's equation to analyze the compatibility between fibers andplastics. What's more, we validated this conclusion by the mechanical properties ofcomposites testing which leads to identical conclusion.