Research And Applications Of Graphene-Coating-assisted Rapid Heat Cycle Molding

With the progress made in the polymer synthesis,manufacturing industries,and the increasingly widespread applications of polymer in the national economy and defense fields,the development of precise and high-performance polymer products and environmental protection requirements have become a research hotspot in the global polymer molding and processing fields.Injection molding,as the most important processing method for polymer,is also facing more urgent innovation needs.Rapid heat cycle injection molding(RHCM)came into being under such a background.RHCM is an environment-friendly and promising injection molding technology based on rapid heating and rapid cooling of mold,which can significantly improve the surface quality,reduce internal stress,improve cavity replication and enhance mechanical properties of plastic products,and broaden the range of injection moldable materials.This work aims to propose and develop a green,chemically-bonded graphene-coating-assisted rapid heat cycle molding(GC-RHCM)technology with high heating efficiency,good temperature uniformity and high temperature stability.Focusing on the scientific and technical issues related to the development of excellent,multi-purpose and low-cost polymer products,systematic research was carried out on three aspects of molding process,micro-morphology and macro-performance.This broke through the core technologies of optimization of the preparation process of chemically-bonded graphene coating,thermal response analysis and wear failure mechanism of graphene film heater,and quality control of GC-RHCM process with high viscosity,poor mobility plastics.GC-RHCM equipment was successfully developed,which greatly reduced RHCM energy consumption,significantly improved molding efficiency,and possessed huge application prospects and technical value in aerospace,Microelectronics,tissue engineering scaffolds and other.fields.The following are the major study and innovations:(1)A novel CVD method was proposed to prepare chemically-bonded graphene coating.The research revealed the control mechanism of the physical and mechanical properties and the failure mechanism of chemica lly-bonded graphene coating;Graphene coating prepared directly on silicon substrate by this method solve the crack defects and weak Van der Waals force after transferring because of the dual enhancement effects between the graphene and the silicon substrate and the graphene monomer layers,and hence achieved industrial applications under high shear and high friction conditions.(2)A new idea was proposed to achieve RHCM using conformal,self-lubricating graphene coating on the mold cavity surface as a thin film heater.A GC-RHCM experimental platform was designed and built to study on the key thermal response characteristics,such as rapid heating and rapid cooling performance,temperature uniformity and stability of cavity surface temperature,which affect the product quality and production cycle of RHCM plastic products.The results showed that the average heating rate and maximum instantaneous heating rate and the highest cavity temperature of graphene coating reached 11.6?/s,16.1?/s and 300?,respectively,which meets the requirements of RHCM of most engineering plastics.It also showed excellent temperature uniformity and stability;The tribological test results showed that the graphene heater has excellent durability when it was prepared at more than 30 mins coating time.(3)GC-RHCM of long glass fiber reinforced polypropylene(LGFRPP)was performed to obtain high-gloss double-date products;The effect of mold temperature on the surface floats,the width and depth of weld lines,mechanical properties and fiber orientation on the LGFRPP products were revealed.The results showed that as the cavity temperature increased,the skin layer,shear layer and core layer of LGFRPP products becomes thinner,thinner and thicker,respectively,the width and depth of the weld lines and surface floats were significantly improved,and the mechanical properties were also enhanced;When the cavity temperature was higher than the melting point of the LGFRPP,the apparent defects,such as weld lines and surface floats were completely eliminated,and the orientation tensor of fibers in the skin layer was basically equivalent to that in the shear layer,indicating that the surface condensation layer was completely eliminated.In addition,a physical model of the melt filling process under the synergy effects of self-lubricating graphene coating and dynamic temperature field was constructed.(4)GC-RHCM technology was utilized to overcome the difficulty of injection molding of pure ultra-high molecular weight polyethylene(UHMWPE)with a molecular weight of 5 million g/mol,and solve the problem of the porous melt front defect generated during the melt filling process and the delamination defect.The influences of cavity temperature on the filling behavior,the delamination defect,mechanical properties,rheological behavior and biocompatibility of UHMWPE products were revealed.The results showed that increasing the cavity temperature could effectively improve the UHMWPE melt filling behavior and enhance the pressure holding effect,and hence improve the porous melt front and delamination defects,and enhance the tensile and impact strengths of UHMWPE products;When the cavity temperature was 140?,the UHMWPE products exhibited an porous-melt-front-free,delamination-free and excellent biocompatibility.(5)Aiming at the shortcomings of conventional microcellular injection molding(MIM)that are difficult to achieve high viscosity UHMWPE molding,a rapid heat cycle MIM method that applied GC-RHCM technology to MIM was proposed.The research revealed the influences of supercritical fluid(SCF)on the melt filling behavior,pore morphology and rheological characteristics of UHMWPE.The results showed that the SCF reduced the viscosity of UHMWPE,and the SCF among UHMWPE powders acted as a lubricant,so that the UHMWPE melt were not compacted too early near the gate,thereby reducing the flow resistance and improving the filling capacity of UHMWPE.Compared to conventional injection molding(CIM)of UHMWPE,the maximum injection pressure of N2 and CO2 assisted MIM decreased by 26%and 22%,respectively.Furthermore,N2 and CO2 decreased the possibility of thermal degradation and molecular chain scission that may occur during the CIM process.This work provided theoretical support for the efficient preparation of porous UHMWPE filter materials,lightweight UHMWPE parts and low-pressure injection molding of solid UHMWPE products.