An experimental and theoretical investigation of transient melt temperature during injection molding

An in-depth study of the effect of molding parameters on melt temperature was carried out, in which the melt temperature was measured with infrared probes. The effect of screw speed, back pressure, shot size, and polymer viscosity on melt temperature during plastication was determined. The melt temperature was not constant during injection, and was found to be as much as 44°C above the barrel temperature. The temperature rise results from viscous dissipation during plastication and adiabatic compression during injection. Measured temperatures are in qualitative agreement with a first order model of the process.     

Correlations between extrusion and injection molding process variables for PVC dry blends

Although thermoplastic extrusion and injection molding have been extensively studied by a large number of authors, very little is known about the correlations between the extrusion and injection molding process variables. This paper describes the various comparable process variables between extrusion and injection molding of PVC dry blends. The Brabender extruder of 19 mm diameter and 25:1 length to diameter ratio and the Szekeley reciprocating single screw injection molding machine were used. PVC dry blends of industrial importance were prepared using a high speed mixer. The four mix formulations based on a commercial grade of PVC were used. Process variables studied during the injection molding were the melt temperature near the nozzle, injection pressure, injection speed, and energy consumption. Process variables studied during extrusion were the melt pressure at the die, power consumption, and the melt temperature at the die orifice. The correlations between the extrusion and injection molding process variables for PVC dry blends have been established.     

注射成型工艺对PBT结晶和降解行为的影响

通过采用不同的注射条件,分别考察了熔体温度、模具温度、螺杆转速、注射速率、背压、保压压力、保压时间、滞留时间等多个重要的注射参数对聚对苯二甲酸丁二醇酯(PBT)小型制件降解程度、结晶形态和力学性能的影响。利用偏光显微镜、DSC、黏度计等,着重研究了各注射工艺参数对制件皮层厚度、结晶度、相对分子质量以及断裂伸长率的影响,从而为优化注射成型工艺过程提供依据。结果表明:熔体温度对制件各项性能的影响最为显著,而螺杆转速、背压、保压压力等的影响相对较小;随着熔体温度的提高和滞留时间的延长,PBT的降解程度迅速加剧,相对分子质量急剧下降,从而使制件断裂伸长率严重降低,力学性能变差。     

A temperature‐dependent adaptive controller. Part II: Design and implementation

A generic online temperature‐dependent adaptive control procedure to redefine the controller parameters was developed from dynamic models to achieve good tracking of injection‐velocity setpoint profiles during filling of a mold cavity. This adaptive control procedure (ACP) incorporates algorithms for process open‐loop testing and modeling, control simulations, and online controller updating. These functionalities are embedded into a main program that provides overall control of mold‐filling velocity. The controller's dynamic matrix is updated as changes in the setpoint melt temperature occur. It was shown that the ACP can provide an effective and systematic approach for controlling injection mold‐filling velocity for any plastic material over its operating melt temperature range. Polym. Eng. Sci. 44:1934–1940, 2004. © 2004 Society of Plastics Engineers.     

PVC degradation during injection molding: Experimental evaluation

This paper focuses on experimental observations of poly(vinyl chloride) (PVC) degradation during injection molding. Degradation of poly(vinyl chloride) has been extensively studied. These studies have been performed in quiescent systems with very little or no strain applied to the sample. However, during processing, the polymer experiences very large deformations, in particular in the case of injection molding. This work demonstrates that the large shear during injection molding causes a significant increase of degradation as compared to studies in quiescent systems. It was also observed that degradation occurs in less than 1/10 the time required for quiescent systems. Finally, the flow geometry also affects the degradation behavior during processing. Understanding the parameters leading to degradation could lead to schemes to avoid it. J. Vinyl Addit. Technol. 10:17–40, 2004. © 2004 Society of Plastics Engineers.     

Degradation mechanism and mechanical properties of PVC in PVC‐PE melt blends: Effects of molecular architecture,content, and MFI of PE

Thermal degradation mechanism and mechanical properties of poly(vinyl chloride) (PVC) in PVC–polyethylene (PE) mixtures with varying types, contents, and melt flow indexes of the PE were studied. The degradation behavior was investigated in terms of decomposition temperature and glass transition temperature, polyene index, and morphology of the PVC in the mix. The results suggested that adding small amounts of PE (5 phr) in PVC‐PE mixtures could thermally stabilize the PVC, as noted by an increase in its decomposition temperature. At higher PE loading, the PVC encountered more degradation as a result of a consumption of the heat stabilizer by PE radicals and the dehydrochlorination reaction. A radical transfer reaction was proposed to explain the degradation mechanism of the PVC in the PVC‐PE melt, specifically a progressive increase of the glass transition temperature of the PVC in the mix as a result of increasing PE content. The PVC‐PE blend using HDPE with high MFI exhibited more pronounced thermal and structural changes of PVC. The mechanical properties of the PVC‐PE blend were very much dependent on the PE content, but slightly affected by the type and MFI value of the PE. The dispersion level of the PE in the PVC phase was found to play an important role in affecting the mechanical properties of the PVC‐PE mixtures. J. VINYL. ADDIT. TECHNOL. 12:115–123, 2006. © 2006 Society of Plastics Engineers     

Rheological behavior and thermal properties of pitch/poly(vinyl chloride) blends

The effect of adding poly(vinyl chloride) (PVC) and coke filler on the rheological behavior and thermal properties of a coal tar pitch was investigated with a view to developing an appropriate viscoelastic binder for the injection molding of graphite components. Dynamic mechanical analysis revealed that the pitch formed compatible blends with PVC featuring a single glass transition temperature (Tg) intermediate to the two parent Tg’s. Adding PVC to the pitch increased melt viscosity substantially and resulted in strong shear thinning behavior at high PVC addition levels. Adding coke powder as filler increased the melt viscosity even further and enhanced shear thinning trends. Pyrolysis conducted in a nitrogen atmosphere revealed interactions between the PVC and pitch degradation pathways: the blends underwent significant thermal decomposition at lower temperatures but showed enhanced carbon yields at high temperatures. Pyrolytic carbon yield at 1000 °C was further improved by a heat treatment (temperature scanned to 400 °C) in air or oxygen. However, carbon yield decreased with addition of PVC. In addition, the degree of ordering attained following a 1 h heat treatment at 2400 °C also decreased with increasing PVC content.     

硬质PVC挤出发泡材料的塑化性能研究

采用Haake转矩流变仪测定了挤出发泡PVC混合料的恒温、升温熔融塑化性能，结果表明：随着PVC树脂聚合度增加，塑化时间和加工转矩增加；随着ACR加工助剂用量和分子质量的增加，塑化时间缩短，转矩增加；ACR抗冲改性剂具有类似ACR加工助剂的塑化改良行为；添加填充剂碳酸钙促进PVC熔融塑化；ADC发泡剂可延缓PVC混合料的塑化速率、提高熔体粘度，添加发泡剂NaHCO3将大大延缓混合料的塑化速率。     

Morphological development during injection molding of self‐reinforcing composites. II: Numerical simulations and analytical predictions

In this study, combined numerical simulation of injection molding and analytical calculations have been used to determine the velocity and elongational strain in the advancing melt front (AMF) region, during the molding of PET/LCP blends, at various injection molding conditions. A model is proposed that establishes the relationship between the aspect ratio of LCP fibers and elongational strain, based on the assumption of an affine deformation of the LCP domains. This model enables us to predict the processing dependent morphology of injection molded PET/LCP blends. The effect of processing parameters on the morphology development during injection molding were investigated. The studies show that injection speed and mold temperature have significant effects on the morphological development of the blends, compared with the effect of the melt temperature. A good correlation between calculated and scanning electron microscopy results was obtained.     

Influence of crystallinity in the curing mechanism of PVC plastisols

The influence of the crystalline areas observed in poly(vinyl chloride) (PVC) the mechanical and thermal properties of PVC plastisols was studied. Several industrial‐degree PVC resins were used to obtain a broad range of molecular weights and processing conditions for PVC plastisols. The gelation process was fully studied at different temperatures and was related to the existence of crystalline areas at high temperatures, even near the glass transition. A simple explanation of the phenomena observed during the gelation of plasticized PVC is proposed, according to the variation in the mechanical and thermal properties at different temperatures. The final gelation was obtained at 140–150°C, which was a lower temperature than those at the beginning of the thermal degradation process. The thermodynamic aspects of the gelation of plasticized PVC were mainly controlled by the PVC resin properties, whereas the plasticizer only influenced the diffusion and stability of the material. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 538–544, 2004     

Pressure and temperature behavior of thermoplastic polymer melts during high‐pressure expansion injection molding

The development of expansion injection molding as new technology for producing thin plastic parts has raised questions about polymer melt behavior in the process of rapid high pressure compression and expansion. To investigate those phenomena, the new in‐line injection molding machine mounted measurement system has been developed. Measuring nozzle equipped with hydraulically driven closing bolts and contact fast response pressure and infrared temperature sensors enabled us to measure the compression and expansion of polymer melts at different starting conditions. Results presented for high impact polystyrene and polyamide show that polymer melt temperature rise is linearly dependent on compression pressure as well as it is dependent on compression speed. Comparable effect of temperature fall has been recorded during the polymer expansion, resulting in no noticeable loss of dissipation energy during this reversible process. Measurements have been compared with modified 2‐domain Tait equation of state. Curve fitting analysis to manufacturer's material data show that measurements fit well with the model, even at very high compression speeds. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Effect of degree of polymerization on gelation and flow processability of poly(vinyl chloride)

The effect of degree of polymerization (DP) on the gelation and flow processability of poly(vinyl chloride) (PVC) was studied. Sheets with adjusted degree of gelation were prepared by rolling rigid pipe formulation suspension PVC compounds with DPs of 800, 1050 and 1300 by changing the milling temperature. Their degrees of gelation were measured with DSC and their capillary flow properties were measured with a capillary rheometer at 150, 170 and 190°C and the effect of DP on the relation between gelation and flow processabilities was studied. Because of the higher shearing heat during milling, the sample with the higher DP had a higher history temperature and thus tended to show a higher degree of gelation. The viscosity increased as the gelation increased. The dependency of viscosity on DP was higher at higher milling and extrusion temperatures and thus at a higher degree of gelation and a lower shear rate. This was assumed to be attributed to the more prominent uniform molecular flow as against the particle flow. The die swell increased with increasing the milling and extrusion temperatures and hence with increasing the gelation. A sample with a lower DP tended to show a larger die swell and this tendency was even more pronounced at the higher extrusion temperature. The melt fracture easily occurred when a sample with advanced gelation was extruded at low temperature. Whereas at low milling temperatures a sample with the lower DP showed a lower critical shear rate at onset of melt fracture, and thus easily generating melt fracture, at high milling temperatures it showed a higher critical shear rate and hence scarcely generated melt fracture. These experimental results were explained by the fact and concept that a sample with a lower DP shows a higher increase in the gelation during extrusion and/or the slighter feature of particle flow as against the uniform molecular flow at the same gelation level. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1915–1938, 2004     

Analysis of low‐density polyethylene‐g‐poly(vinyl chloride) copolymers formed in poly(vinyl chloride)/low‐density polyethylene melt blends with gel permeation chromatography and solid‐state 13C‐NMR

Gel permeation chromatography (GPC) and solid‐state ¹³C‐NMR techniques were used to analyze the structural changes of poly(vinyl chloride) (PVC) in blends of a low‐density polyethylene (LDPE) and PVC during melt blending. The GPC results showed that the weight‐average molecular weight (M_w) of PVC increased with LDPE content up to 13.0 wt % and then decreased at a LDPE content of 16.7 wt %, whereas the number‐average molecular weight remained unchanged for all of LDPE contents used. The ¹³C‐NMR results suggest that the increase in M_w was associated with the formation of a LDPE‐g‐PVC structure, resulting from a PVC and LDPE macroradical cross‐recombination reaction during melt blending. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3167–3172, 2004     

A temperature‐dependent adaptive controller. Part I: Controller methodology and open‐loop testing

Currently, the controllers for achieving a desired injection velocity setpoint profile are independent of processing conditions in plastic injection molding. The dynamics of the reciprocating screw during injection mold filling is complex and temperature‐dependent. This complexity is based on process parameters that are nonlinear, which can vary spatially in time. Open‐loop tests were performed on two polymers at three melt temperatures and three mold‐fill velocity regimes: low, medium, and high. These tests were based on close‐loop injection mold‐fill setpoints and a derived voltage velocity relationship for the injection velocity hydraulic valve. The results of the open‐loop tests show that mold‐filling injection velocity is polymer‐ and melt temperature‐dependent. Polym. Eng. Sci. 44:1925–1933, 2004. © 2004 Society of Plastics Engineers.     

New developments in melt rheology aid formulating rigid vinyl compounds with improved extrusion processing

This paper describes a new approach to the rheological characterization of PVC compounds using a capillary rheometer. Since the control of the thermal degradation rate of rigid PVC is very critical in extrusion, a new quantitative method of measuring the true degradation rate of PVC is proposed for formulating rigid vinyl compounds. The usefulness of this new technique is demonstrated in formulating PVC compounds with the lowest rate of degradation measured on the Kayeness capillary rheometer. This study shows a very good correlation between the capillary rheometer data and the extrusion melt temperature, melt viscosity, and the rate of degradation of PVC. The ideal melt temperature for extrusion is determined from the rheology data of each PVC compound to attain the longest run time. The study also shows how to measure the true melt temperature in extrusion, an important variable, to control the rate of degradation in processing. The results of this study show how the new rheology technique can be used as a practical tool for product development, quality control of the PVC compounds, and the development of optimum extrusion parameters.     

Synthesis of a novel polyester plasticizer based on glyceryl monooleate and its application in poly(vinyl chloride)

The use of bio‐based polymeric plasticizers could expand the application range of plasticized poly(vinyl chloride) (PVC) materials. In this study, a novel bio‐based polyester plasticizer, poly(glutaric acid‐glyceryl monooleate) (PGAGMO), was synthesized from glutaric acid and glyceryl monooleate via a direct esterification and polycondensation route. The polyester plasticizer was characterized by gel permeation chromatography, ¹H‐nuclear magnetic resonance, and Fourier‐transform infrared spectroscopy. The plasticizing effect of PGAGMO on PVC was investigated. The melting behavior, thermal properties, and mechanical properties of PVC blends were studied. The results showed that the PGAGMO could improve the thermal stability and reduce the glass transition temperature of PVC blends; when phthalates were substituted by PGAGMO in PVC blends, the thermal degradation temperature of PVC blends increased from 251.1°C to 262.7°C, the glass transaction temperature decreased from 49.1°C to 40.2°C, the plasticized PVC blends demonstrated good compatibility, and the decrement of the torque and the melt viscosity of PVC blends were conducive to processing. All results demonstrated that the PGAGMO could partially substitute for phthalates as a potential plasticizer of PVC. J. VINYL ADDIT. TECHNOL., 22:514–519, 2016. © 2015 Society of Plastics Engineers     

Processing thermal stability and degradation kinetics of poly(vinyl chloride)/montmorillonite composites

Thermal stability of polyvinyl chloride (PVC) based montmorillonite composites with either sodium montmorillonite (MMT) or alkyl ammonium ion modified montmorillonite (OMMT) were investigated by thermogravimetric analysis. The apparent activation energies associated with the first thermal degradation stage were calculated by the methods of Flynn–Wall–Ozawa and Kissinger in nitrogen atmosphere at several different heating rates. The processing thermal stability of PVC and PVC/MMT(OMMT) composites was also discussed. Increase of mixing torque did not result in a larger intercalation extent of PVC on MMT; instead, it unexpectedly induced discoloration of PVC and then deteriorated the processing stability, especially in the presence of OMMT. The apparent activation energies in the first thermal degradation stage exhibited little difference among PVC, PVC/MMT, and PVC/OMMT composites, and the kinetic compensation effect of S_p^* kept a constant value, indicating that the thermal stability and thermal degradation mechanism of PVC were not affected by the presence of either MMT or OMMT, although the processing discoloration of PVC is observed for PVC/OMMT composite. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1521–1526, 2004     

PVC/montmorillonite nanocomposites based on a thermally stable,rigid‐rod aromatic amine modifier

Two kinds of polyvinyl chloride (PVC)/montmorillonite (MMT) nanocomposites were prepared by the melt intercalation method based on a thermally stable, rigid‐rod aromatic amine modifier and a commonly used 1‐hexadecylamine. The information on morphological structure of PVC/MMT nanocomposites was obtained using XRD and TEM. The mechanical, thermal, and flame retardant properties of the nanocomposites were characterized by universal tester, DMA, TGA, and cone calorimeter. The degree of degradation of PVC was studied by ¹H‐NMR. MMT treated by the aromatic amine exhibited better dispersibility than that treated by 1‐hexadecylamine. The nanocomposites, based on this MMT, consequently exhibited better mechanical, thermal, and flame retardant properties and lower degradation degree than those based on 1‐hexadecylamine‐treated MMT. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 567–575, 2004     

Effect of process conditions on birefringence development in injection-molded parts. I. Numerical analysis

Analysis of the injection-molding process based on Leonov viscoelastic fluid model has been employed to study the effects of process conditions on the residual stress and birefringence development in injection-molded parts during the entire molding process. An integrated formulation was derived and numerically implemented to solve the nonisothermal, compressible, and viscoelastic nature of polymer melt flow. Simulations under process conditions of different melt temperatures, mold temperatures, filling speeds, and packing pressures are performed to predict the birefringence variation in both gapwise and planar direction. It has been found that melt temperature and the associated frozen layer thickness are the dominant factors that determine the birefringence development within the molded part. For a higher mold temperature, melt temperature, and injection speed, the averaged birefringence along gapwise direction is lower. The birefringence also increases significantly with the increased packing pressure especially along gate area. The simulated results show good consistency with those measured experimentally. © 1995 John Wiley & Sons, Inc.     

Research on a New Variotherm Injection Molding Technology and its Application on the Molding of a Large LCD Panel

The polymer injection products produced by using the current injection molding method usually have many defects, such as short shot, jetting, sink mark, flow mark, weld mark, and floating fibers. These defects have to be eliminated by using post-processing processes such as spraying and coating, which will cause environment pollution and waste in time, materials, energy and labor. These problems can be solved effectively by using a new injection method, named as variotherm injection molding or rapid heat cycle molding (RHCM). In this paper, a new type of dynamic mold temperature control system using steam as heating medium and cooling water as coolant was developed for variotherm injection molding. The injection mold is heated to a temperature higher than the glass transition temperature of the resin, and keeps this temperature in the polymer melt filling stage. To evaluate the efficiency of steam heating and coolant cooling, the mold surface temperature response during the heating stage and the polymer melt temperature response during the cooling stage were investigated by numerical thermal analysis. During heating, the mold surface temperature can be raised up rapidly with an average heating speed of 5.4°C/s and finally reaches an equilibrium temperature after an effective heating time of 40 s. It takes about 34.5 s to cool down the shaped polymer melt to the ejection temperature for demolding. The effect of main parameters such as mold structure, material of mold insert on heating/cooling efficiency and surface temperature uniformity were also discussed based on simulation results. Finally, a variotherm injection production line for 46-inch LCD panel was constructed. The test production results demonstrate that the mold temperature control system developed in this study can dynamically and efficiently control mold surface temperature without increasing molding cycle time. With this new variotherm injection molding technology, the defects on LCD panel surface occurring in conventional injection molding process, such as short shot, jetting, sink mark, flow mark, weld mark, and floating fibers were eliminated effectively. The surface gloss of the panel was improved and the secondary operations, such as sanding and coating, are not needed anymore.