Surface Grafting Of Hyperbranched Dendritic Polymer Onto Sisal Fiber And Its Influence On The Mechanical Properties Of The Composites

First of all,a hyperbranched polymer with terminal amino group（HBP-NH2）was synthesized by varying reactive monomer synthesis of methyl acrylate（MA）and diethyltriamine（EDTA）.Many kinds of sisal fiber surface modification methods were taken,so that the HBP-NH₂ was grafted onto the surface of sisal fiber.Then the fiber composite materials was prepared with modified fibers and a thermoplastic resin,mechanical properties of which are improved.Secondly,by stepwise method,the dendrimer polyamidoamine（PAMAM）was grafted onto the surface of sisal fiber,that was synthesized with methyl acrylate（MA）and ethylene diamine（EDA）.The mechanical properties of fiber composite materials prepared with the modified fibers and thermoplastic resin has been significantly improved.Finally,In order to simplify the experimental conditions,extruder blending method was used to modify sisal fiber and prepare composite materials,significant improvement in the mechanical properties of the composites was not found.While infrared absorption spectroscopy（FT-IR）,gel permeation chromatography（GPC）,thermal gravimetric analyzer（TGA）,universal testing machine,impact testing were used to characterize the structure and the performance of the product.Experimental results show that the higher molecular weight and uniform HBP-NH₂ can be obtained using the following method:MA was slowly added dropwise to an equimolar amount of EDA methanol solution in a nitrogen atmosphere and at the temperature of0℃.After the addition,the product was reacted at the temperature of 25℃for 48h.Then the product was reacted in a tomato form flask of a rotary evaporator under reduced pressure and slowly warmed to 150℃.The HBP-NH₂ was successfully grafted onto the sisal fiber surface with maleic anhydride（MAH）which is a coupling agent and p-toluenesulfonic acid which is a catalyst.The mechanical properties of fiber composite materials prepared with the modified fibers and a thermoplastic resin has been improved.By extrusion blending method,the mechanical properties of prepared modified sisal fiber composite materials increased slightly.The results showed that when the MAH and HBP-NH₂ were in an amount of 1%and 2.5%,the mechanical properties of modified composites was the best.By gradually grafting PAMAM onto sisal fiber surface,modified fiber composite material was prepared,its mechanical properties has been significantly improved,the results showed that the highest grafting rate can be obtained with a bath ratio of 1:25,at the temperature of 50℃for 24h in Michael addition reaction;at the temperature of 60℃for 12h in amidation reaction.The volume fraction of MA of methanol solution was 4%,the amount of EDA was twice the amount of MA inG1.0.Doubling the amount of reagents in the next generation.Comparingwith the alkali treatment sisal fiber composite materials,the tensile strength increased by 28.55 percent,the impact strength increased by 45.67 percent,the flexural strength increased by 12.89percent,and the flexural modulus increased by 10.44 percent.In summary,this study succeeded in preparing dendrimer-modified sisal fiber/thermoplastic resin composite material,and it has significantly improved its mechanical properties.