| Non-equilibrium thermodynamics theory is that: for an open system,if it maintain a sufficiently negative entropy flow which from the environment,to offset the entropy that came from itself irreversible process,making the system total entropy decreases gradually,and maintaining in a low entropy than the equilibrium of non-equilibrium steady state,the irreversible process inevitably leads to system evolvement from disorder to order,which is far from equilibrium state and orderly the possibility of spatiotemporal ordered dissipative structure.According to the thermodynamic non-equilibrium theory,this paper designed the non-equilibrium injection molding mold and the control device by itself.Through the precise regulation of the thermodynamic state of the mold cavity,the negative entropy flow was introduced into the blend system while molding,and the phase separation gradient structure was formed by self-organization.Through the research of non-equilibrium molding of crystalline polymer polypropylene and its composite system,the in-mold self-organization mechanism and morphology control mechanism of gradient ordered structure are revealed.(1)Design of non-equilibrium injection molding mold and control device:In order to achieve the installation and fixation of the unbalanced molding mold on the micro vertical plastic injection molding machine,the vertical mold mounting base was redesigned and made and the original mold mounting base was replaced for the special structure of the Mini Jet Pro precision micro injection molding machine,to ensure that the unbalanced mold can be installed and disassembled correctly,reliably and quickly.In addition to meeting the design requirements of the basic structure and function of the injection mold,the key design solves the introduction of a stable directional negative entropy flow in the mold cavity and the cooling medium required for quenching and solidification,which realizes fast,stable and precise control of the thermodynamic state of the melt in the cavity.Through the analysis of the traditional injection molding cycle process,the non-equilibrium molding cycle process route was proposed,and the original injection molding machine control system was modified to meet the requirements of the non-equilibrium molding process and the injection molding process was realized.At the same time as the basic requirements,it can accurately,stably and quickly regulate the thermodynamic state of the melt in the cavity,ensuring reliable control of non-equilibrium injection molding.(2)Formation mechanism and evolution law of polypropylene gradient crystallization structure:In traditional balanced injection molding,the skin layer of the melt contacting the cavity wall is rapidly cooled by contact with a mold with a large temperature difference.The molecular chains are too late to arrange and crystallize and are frozen to form a "skin" layer with low crystallinity.The internal polymer melt dissipates heat slowly,and has a certain time and energy to arrange and crystallize to form a "core" part with high crystallinity,the final condensed state structure is "skin-core structure".During the cooling and solidification process,the core and the entire thickness of the melt quickly passed 120 ?,making it difficult to achieve ?-? growth conversion.Therefore,the crystal form is mainly ? crystal.In non-equilibrium injection molding,the temperature of the energy inflow side is higher due to the introduction of negative entropy flow into the cavity.In this study,they reached 100,120,140,and 160 ? respectively,while the temperature of the energy outflow side remained at the same room temperature(15 ?)as in traditional injection molding,this results in a linear temperature distribution in the cavity along the direction of negative entropy flow.After the PP melt at 170 ? is injected into the cavity with this temperature gradient,the skin melt contacting with the Ti and To side cavity walls will quickly approach its temperature,while the internal melt will slowly fall back to the linear distribution temperature before filling,and then under the different negative entropy flow intensity and dissipation time,the PP molecular chain has sufficient time to be oriented and arranged,and then develop and grow.Since the temperature along the direction of negative entropy flow in the cavity is approximately linearly distributed,its nucleation ability and growth rate of crystal grains also follow this distribution change,and finally format heterogeneous condensed matter structure that the crystallinity,grain size,hardness and other properties are gradient distribution along the direction of negative entropy flow.The growth rate of ? crystal is the highest at 120 ?,and the intensity of negative entropy flow can be controlled to indirectly control the position of the temperature range of 120 ? in the direction of negative entropy flow,thereby controlling the growth area of ? crystal.The temperature of the energy inflow side of GPP120/15-30 is always maintained at 120 ? during the holding time of negative entropy flow dissipation,so the crystallinity of the ? crystal on the energy inflow side is reaching the peak value 7.96 %,higher than 4.14 % of GPP100/15-30?5.64 % of GPP140/15-30 and 5.60 % of GPP160/15-30,which is 22.7 times that of the traditional balanced injection molding core of 0.35 %.Therefore,adjusting the intensity of negative entropy flow and the time for holding pressure dissipation can effectively control the crystallinity and grain size distribution in the direction of negative entropy flow,as well as the ratio of ? crystal and ? crystal,and the distribution area of ? crystal.(3)Formation mechanism and control method of gradient structure of polypropylene/lead-tin alloy under non-equilibrium injection molding conditions:In the traditional process of injection molding,the cavity is in a near-thermodynamic equilibrium state,the total entropy of the system is far greater than zero,and the components of the blended melt in the cavity will tend to be the most chaotic and random distribution,formed uniformly distributed sea-island microphase separation structure by cooling and solidification.In the time before the blended melt is injected into the cavity and the pressure holding time after injection,the cavity is continuously given a directional,stable negative entropy flow whose absolute value greater than the internal entropy,so that the total entropy of the system is always less than zero and stable maintain a non-equilibrium steady state with a lower entropy than the equilibrium state.The heat flow and material flow caused by the negative entropy flow will cause the high melting point(weak thermal mobility)components segregate and stay on the low-temperature energy outflow side,and the low melting point(strong thermal mobility)components segregate and stay on the high-temperature energy inflow side in the melt,and eventually forms a heterogeneous gradient phase separation structure.Changing the intensity of the negative entropy flow can change the segregation speed of each component and adjust the distribution area and concentration of each component in the direction of the negative entropy flow.Reducing the intensity of the negative entropy flow can make the gradient change area evolve from the local area on the energy outflow side of the high negative entropy flow intensity to the full-section area,and can reduce the concentration difference between the energy inflow side and the outflow side.On the contrary,increasing the intensity of the negative entropy flow can gradually compress the gradient area to the local area on the outflow side,and even form a step-type phase separation structure,and can increase the concentration difference between the energy inflow and outflow sides,accelerate the component segregation,shorten the required pressure holding and dissipation time.By adjusting the pressure holding and dissipation time,the segregation process can be terminated at a certain time point during the migration and segregation of each component,or sufficient evolutionary development time can be given to achieve control of the morphological structure.Therefore,by comprehensively adjusting the intensity of the negative entropy flow and the holding pressure dissipation time,the desired topography structure can be formed in a relatively short holding pressure dissipation time,which is beneficial to shorten the molding cycle and improve productivity.Regulate the direction of gravity so that it is in the same direction as the negative entropy flow to promote the development of gradient morphology,control the type of gradient morphology,and shorten the dissipation time of negative entropy flow and shorten the molding cycle.It is also possible to reverse the gravity setting to adjust the shape and type of the gradient structure.Molecular weight and molecular weight distribution of polymer components and the temperature range of non-equilibrium molding can be control to adjust viscosity of polymer components during non-equilibrium molding,control the morphology and type of the gradient structure,and shorten the necessary pressure holding dissipation time.Regulating the thermodynamic state of the cavity can control the micro-phase separation morphology structure of the injection molded product section,and can selectively prepare isotropic and uniform sea-island micro-phase separation structure,or heterogeneous gradient type or even step type micro-phase separation structure,obtain gradient functional materials or products,achieve effective control of morphological structure and product performance.The intensity of negative entropy flow,the pressure holding and dissipation time,the direction of gravity,and the viscosity of the polymer component all affect the heterogeneous structure and morphology of the final product.Reasonably controlling the various elements is conducive to obtaining a variety of heterogeneous morphology and structure,realize colorful functions and applications,shorten the molding cycle,at the same time meet the requirements of industrialization for production efficiency,and control cost,suitable for mass production of heterogeneous gradient structure materials and parts,with extremely bright industrial application prospects. |
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