Bamboo And Hemp Fiber Reinforced Polypropylene Prepreg For Winding

Winding molding is a process in which continuous fibers or tapes impregnated with resin glue are wound on a core mold according to a certain rule,and then cured and demolded into products.It has the advantages of high production efficiency,strong designability,and high accuracy.Winding molding often uses a thermosetting resin matrix and artificial fibers as raw materials.However,natural fibers have a wide range of sources,low prices,energy conservation,and better specific strength and specific modulus,at present,most studies have proved that natural fibers have the potential to replace petroleum products.Compared with thermosetting resins,thermoplastic resins have the unique advantages of damage resistance,impact resistance,chemical and solvent resistance,unlimited shelf life,low storage costs,weldability and recyclability.In this paper,hemp and bamboo fibers were selected as the reinforcement of polypropylene(PP)to prepare thermoplastic prepreg tapes.On the premise of considering the mechanical strength of PP matrix itself,PP with high melt flow index was adopted to solve the problems of difficult impregnation due to thermoplastic resin's high viscidity,and the fiber is treated with laccase and alkali to improve the compatibility of the resin matrix and natural fiber.In addition,the self-developed preform roll process can realize the preparation of long natural fiber reinforced thermoplastic prepreg.By investigating the physical and mechanical properties,rheological properties,thermal properties and chemical properties,the preparation process and forming principle of the new prepreg strip were studied systematically,and the theoretical model was analyzed.The main research contents and conclusions of the paper are as follows:1?Study on improving the properties of jute fiber/PP prepreg through fiber modification and PP matrix optimizationAiming at the problems of poor compatibility between biomass fibers and thermoplastic resins,and the high melt viscosity of thermoplastic resins,it is difficult to penetrate into the fiber twines.In the study,alkali and laccase were used to treat jute twine to improve the compatibility between jute rope and PP.three types of melt index(MFI)were selected:10.9 g/10 min,27.8 g/10 min,and 50.0 g/10 min of PP for impregnation tests to determine the best MFI for impregnation simultaneously.The results show that both alkali treatment and laccase treatment can roughen the fiber surface,reduce the fiber surface polarity,and effectively improve the interface bonding strength between jute rope and PP.However,excessive alkali treatment will remove components such as hemicellulose,lignin,and pectin,causing a great loss of strength of the fiber itself.Laccase treatment was mild and only acted on lignin,which significantly improved the tensile and dynamic mechanical properties of the prepreg strip under the premise of maintaining its own strength to a large extent.The amount of PP impregnated into jute twine increased with the increase of MFI.However,PP with higher MFI has poorer mechanical properties.Therefore,it is necessary to balance the impregnation effect with the tensile strength of PP.Based on the results of various performance tests,the prepreg tapes prepared with lassase treated hemp twinee and PP with MFI of 27.8 g/10 min have high storage modulus,loss modulus and tensile properties.According to the calculation of the simulation formula,the nominal pressure of the pipe wound with this prepreg tape can reach 2.88 MPa(GB/T 13663-2000,the nominal pressure required in the standard of polyethylene pipes for water supply is 2.3 MPa).2?Study on the technology and properties of bamboo raw fiber/PP composites prepared by extrusion moldingIncreasing the length of the reinforcing fiber can significantly improve the mechanical properties of the composites,but with the increase of the fiber length,the problems of fiber entanglement,uneven mixing with thermoplastic particles,and difficult feeding are gradually produced.Therefore,in the study,a PP film was used as a carrier to prepare prefabricated rolls to achieve pre-mixing,melt blending,and molding of bamboo fiber with a length of more than 40 mm.The effects of two kinds of fiber length(3-20mm and 40-120mm),three kinds of fiber/PP ratio(3:7,4:6,5:5),two kinds of rotors(roller rotor,more rotor flanging,large flanging rotation angle;banbury rotor,less flanging and small flanging rotation angle)on the properties of composites are mainly studied.and analyze the melt mixing process of prefabricated rolls to optimize the long fiber reinforced composite material preparation technology.The results show that during the melt mixing process,the long bamboo fiber is obviously shortened by the twin-screw rotor.Among the two types of rotors,the banbury rotor with less rotor flanging,small flanging rotation angle has less damage to the bamboo fiber.In the composite system,the fiber length is larger,the performance of the composites is higher,and it has the potential of mixed long fiber composite.The strengthening effect of long bamboo fiber on the composite system is obviously better than that of bamboo powder,but the long bamboo fiber is easy to agglomerate,so the control of its amount is extremely critical.When the long bamboo fiber is added at 40%,the fiber dispersion and orientation effect is better,which effectively restricts the polypropylene movement,improves the storage modulus and tensile properties of the composites.Although the raw bamboo fiber length has no significant effect on the water absorption deformation of the composite,the longer raw bamboo fiber can better reduce the thermal expansion deformation and creep deformation of the composite.3?Study on improving the performance of raw bamboo fiber/PP prepreg tape by fiber modificationImproving the interfacial compatibility between natural fiber and thermoplastic polymer has always been a hot and difficult topic in the research of natural fiber reinforced thermoplastic polymer composites.Raw bamboo fiber was treated with laccase,which is green,specific and mild in treatment conditions,to improve the interface bonding strength between bamboo fiber and PP matrix.The amounts of laccase/bamboo fibers were 40U/g,50U/g,and 60U/g respectively.The results show that laccase can oxidize lignin on the surface of bamboo fibers,reduce surface polarity and increase surface roughness,thereby improving the interface bonding between bamboo fibers and PP matrix;increasing the complex viscosity,storage modulus and loss factor of the composite system.However,the high amount of laccase will cause loose binding between the microfibril bundles and weaken the strength of the fiber itself.When the amount of laccase is 50U/g bamboo fiber,the loss of bamboo fiber strength is small,and the tensile properties of PP prepreg tapes are the best.The longitudinal tensile strength is 58.72MPa,the tensile modulus was 2.17GPa,and the hoop tensile strength was 114.58 GPa,the elongation at break was 21.33%.After the bamboo fiber is treated with laccase,the bending flexibility of the prepreg tapes is also increased,the thermal expansion deformation and creep deformation of the prepreg tapes are inhibited,the thermal stability is improved.4?Exploration of winding process and performance simulation of raw bamboo fiber reinforced polypropylene composite ringThe tensile force that the thermoplastic matrix can withstand gradually decreases with increasing temperature,and the non-continuous raw bamboo fiber cannot bear the winding tension required by heating winding.Therefore,the non-continuous bamboo fiber-reinforced prepreg is difficult to prepare the composite tube or ring by the conventional heating and melting winding process.The techniques of "tension-free hot winding" and "cold winding"have been developed.The hoop tensile and ring stiffness properties of the ring were tested,and the stress and strain distributions during the tensile and ring stiffness tests of the composite ring were analyzed theoretically by finite element modeling.The results show that the two winding methods can achieve the preparation of raw bamboo fiber reinforced PP composite ring,and both methods have no obvious effect on the hoop tensile strength and ring stiffness of the composite ring.The ring stiffness of the composite ring can reach grade S2 in the nominal ring stiffness classification of pipe fittings in the national standard QB/T1916-93 approved by the industry standard.The results of finite element simulation show that when the ring is stretched,the stress and strain of raw bamboo fiber and PP matrix are concentrated on both sides of the ring parallel to the tensile direction,and the maximum stress of raw bamboo fiber is obviously larger than that of PP matrix,but the strain is smaller than the PP matrix.When the composite ring is under pressure,the stress is mainly concentrated on the up and down ends of the composite ring,followed by the left and right ends.The fiber stress distribution area is larger than the PP matrix stress distribution area,which is the result of the effective stress transfer between fibers.When subjected to external forces,the PP matrix first undergoes yield failure.In conclusion,the mechanical properties of the composite ring can be optimized from two aspects:(1)Coordinating the strain difference between the resin matrix and the reinforcing fibers,thereby reducing the stress concentration caused by the inconsistent strain;(2)Improve the interface bonding between the resin matrix and the reinforced fiber,so that the interface phase can transfer the stress between the resin and the fiber effectively,thereby achieving mutual restraint between the resin matrix and the reinforcing fiber.