Research On Physical Modification And Forming Properties Of ABS/PMMA For Rapid Heat Cycle Molding Process

Injection molding technology is the main molding method of plastics. However there are many problems of parts produced by conventional injection method, such as flow mark, weld line, poor surface quality and so on. In order to improving surface quality of plastics, spraying and coating are usually used which will cause the environmental pollution and the waste of time, materials and energy. Rapid heat cycle molding (RHCM) process which is raised in recent years resolved these problems successfully. However rapid heat cycle molding process put forward higher requirements on the gloss, hardness, flow and mechanical properties of materials. ABS copolymer is a thermoplastic with excellent comprehensive properties, however, its hardness and gloss still be further improved. PMMA is a hard thermoplastic and has superior optical properties. Blending of ABS with PMMA is a useful way to improve the hardness and gloss of ABS. Although ABS/PMMA can meet the requirements of rapid heat cycle molding process, there still exist some problems in ABS/PMMA, such as high cost and lack of toughness and heat resistance. However, the research on ABS/PMMA system is quite little, thus it is very important to study on the blending modification of ABS/PMMA system and its application in RHCM process.Several materials such as ABS/PMMA, ABS/PMMA/ABS HRP, ABS/PMMA/nano-CaCO3 and ABS/PMMA/PTW were prepared by using the melt blending method in this paper. The effect of plastic additives, toughening agent, nanoparticles and ceramic whiskers on mechanical, flow, thermal and surface properties of materials was analyzed. Finally, ABS/PMMA and ABS/PMMA/nano-CaCO3 standard samples were produced using rapid heat cycle molding process. Then the surface quality and internal properties of samples produced by conventional injection process and rapid heat cycle molding process were compared. And valuable theoretical achievements applied to new material development and plastic productions were acquired.Materials were blended in a co-rotating twin screw extruder. Effect of ABS/PMMA ratio and various plastic additives such as antioxidant, Lubricant and compatibilizer on properties of ABS/PMMA were studied, and influence of number of extrusion on properties of ABS/PMMA was also been researched. It was indicated that the strength and hardness of blends both increased but the toughness of blends decreased with the increase of PMMA content. During the blending process, the properties of blends began to deteriorate due to the cross-linking and scission of polymer chains under the action of heat and shear stress, however, the antioxidant can prevent the deterioration of material properties in blending process effectively. Lubricant in this study can reduce the friction between materials and processing machine in order to improve the gloss of plastic, on the other hand it played a plastic role in the blends and made the toughness of blends improved. The degree of compatibility between ABS and PMMA was not enhanced by using SMA, instead, the strength of blends increased and the toughness of blends decreased because of the ring structure of SMA. Increasing the number of extrusion can improve the uniformity of blends and then enhance the mechanical properties of plstic, especially the impact strength.Extrusion processing parameters were optimized by using taguchi method. The impact factors of various extrusion processing parameters were calculated. Based on the optimized extrusion processing parameters, ABS/PMMA was modified by using ABS high rubber powder (ABS HRP) as toughening agent. As the polymer material is a viscoelastic material, different mechanical relaxation phenomenon can be observed when materials subject to external force. So the effect of strain rate on tensile properties of ABS/PMMA system was studied by changing the tensile rate in this paper. The results indicated that extrusion processing parameters had little effect on the properties of ABS/PMMA. ABS HRP is a compound rubber modifier with a "core-shell" structure similar with ABS. So the toughness of ABS/PMMA system was greatly improved, although the strength and modulus were slightly decreased by adding ABS HRP. ABS/PMMA/ABS HRP was strain rate sensitive material. There existed a brittle-ductile transition between 7.25×10-5s-1 to 7.25×10-1s-1 strain rate.Nanoparticles have many better properties than conventional materials. In order to reduce cost, nano-CaCO3 particles were chosen to fill ABS/PMMA. The influence of size and content of nano-CaCO3 on various properties of ABS/PMMA was analyzed in this paper. It is difficult for inorganic nanoparticles to disperse in resin matrix. Therefore, the effect of surface treatment of nano-CaCO3 on flow and mechanical properties of composite material was studied. And stearic acid, titanate coupling agent, aluminium-titanium compound coupling agent and collaborative use of aluminium-titanium compound coupling agent and stearic acid were compared. Furthermore, the effect of titanate coupling agent content and surface treatment method were also studied in this paper. Finally, the interfacial adhesion between nano-CaCO3 particles and polymer matrix was calculated using adhesion coefficient B and debonding angleθ. It showed that nano-CaCO3 can improve MFI of material when the dosage was smaller than 4 wt%. The MFI of ABS/PMMA/nano-CaCO3 composite material increased linearly with temperature. The size and content of nano-CaCO3 had little effect on tensile properties of ABS/PMMA/nano-CaCO3 composite material. However the impact strength decreased deeply with the increase of nano-CaCO3. Particles with a mean diameter of 100nm are better than particles with a mean diameter of 25 nm for the toughness of composites. Surface treatment of nano-CaCO3 can improve the adhesion between inorganic particles and resin matrix effectively. Considering the mechanical properties of ABS/PMMA/CaCO3 composites, collaborative use of aluminium-titanium compound coupling agent and stearic acid is best for surface modification of nano-CaCO3 particles in this paper. And the dispersion quality of this kind of nano-CaCO3 is best. Titanate coupling agent can react more sufficiently with nano-CaCO3 particles in solution method. But nano-CaCO3 particles are apt to bond to blocks in solution method which is not good for dispersion. And coupling agent can increase the MFI and tensile strength of ABS/PMMA/nano-CaCO3 composites. The Izod impact strength of composits increased first and then decreased as the coupling agent increased.Polymer modified with whiskers is one of research hot points in polymer matrix composite material. PTW has excellent mechanical, thermal properties and low cost. PTW was blended with ABS/PMMA in this paper and the effect of PTW on flow, mechanical and thermal properties of ABS/PMMA was researched. PTW can improve the thermal properties of composite material effectively but reduce flow properties of composite material. However, the tensile strength of composite material would be increased with lower content of PTW, but it would be decreased when the dosage of PTW is high. The toughness of composite material became to deteriorate by adding PTW.Based on the physical modification of ABS/PMMA, temperature control system and electrical heating mold developed by our own lab were linked with plastic injection machine to construct RHCM injection system. ABS/PMMA and ABS/PMMA/nano-CaCO3 standard samples were formed by using RHCM process. Different mold surface temperatures were obtained by changing the heating time of mold. Then the effect of mold surface temperature on surface and mechanical properties of plastic products was analyzed. The forming characteristics and properties of ABS/PMMA and ABS/PMMA/nano-CaCO3 were compared. Finally, double-gate samples were produced in RHCM process, the influence of mold surface temperature on morphology and strength of weld line were studied. It indicated that plastic products made by RHCM process have higher gloss compared by conventional injection process. When the mold surface temperature reached the glass temperature of resin, the gloss of ABS/PMMA and ABS/PMMA/nano-CaCO3 are in the same level. And the weld line of products can be eliminated during RHCM process. The orientation of polymer chain and internal stress both decreased because of higher mold temperature. When the temperature of mold is a little higher than the glass temperature of resin, the comprehensive properties of products is the best.