Study on mechanical properties and material distribution of sandwich plaques molded by co‐injection

In the sandwich injection molding process (co‐injection), two different polymer melts are sequentially injected into a mold to form a part with a skin/core structure. Sandwich molding can be used for recycling, improving barrier and electrical properties, or producing parts with tailored mechanical properties. In this study the evaluation of flexural modulus and impact strength of co‐injected plaques have been investigated. Virgin and short glass fiber reinforced (10 and 40%) polypropylene were used in six different combinations of sandwiched layers. The skin and core thicknesses were measured by optical microscopy and used to calculate the theoretical flexural modulus, which was compared to the experimentally measured modulus. Fiber orientation states were also observed by scanning electronic microscopy (SEM) at some specific locations and their effect on mechanical properties discussed. The experimental results indicate that an important improvement in transverse modulus, near the gate, is obtained when the virgin polypropylene (PP) is used as a skin and 40% short glass fiber polypropylene (PP40) as core. When both skin and core are made of PP40, the flexural moduli are slightly higher than conventionally injected PP40. POLYM. COMPOS. 26:265–275, 2005. © 2005 Society of Plastics Engineers.     

Assessing the effect of processing variables on the mechanical response of polysytrene molded using vibration‐assisted injection molding process

The present work is focused on the study of vibration‐assisted injection molding (VAIM) process, using polystyrene as a model polymeric system. This recently developed polymer processing operation is based on the concept of using motion of the injection screw to apply mechanical vibration to polymer melt during the injection and packing stages of injection molding process, to control the polymer behavior at a molecular level, which would result in improvements/alterations to the mechanical behavior of molded products. In this study, the afore‐mentioned concept was verified experimentally from monotonic tensile experiments and birefringence measurements of VAIM molded polystyrene in comparison with those of conventional injection molding process. The results of our study indicate that the actual degree of strength improvement depends on at least four parameters, namely, vibration frequency, vibration amplitude, vibration duration, and the delay time between the injection start and the vibration start. Furthermore, when these parameters were optimized, as much as a 28% strength improvement was observed, accompanied by an increase in toughness. Furthermore, birefringence measurements revealed that VAIM processing significantly altered the residual stress distribution throughout final products, but it did not, however, change the material density in the products. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Co‐injection molding of PVC with other thermoplastics: Processing,properties, and applications

Rigid poly(vinyl chloride) (PVC) was co‐injected with glass‐fiber‐reinforced PVC (GFR‐PVC), polypropylene (PP), acrylonitrile‐butadiene‐styrene copolymer (ABS), and polycarbonate (PC) by using the Mono‐sandwich co‐injection process. Up to three through‐thickness skin‐core morphologies were observed along the length of the sample. Near the gate, the core was always a single, continuous layer. In some cases, the core diverged into multiple or discontinuous layers. Farther from the gate, flow of the core ceased, leaving a skin‐only region. The skin and core layers were more uniformly distributed through the test plaque when injection speed was low. Adhesion between PVC and PP was poor. Skin and core layers delaminated, and mechanical properties were poor. The PVC adhered well to GFR‐PVC, ABS, and PC. No layer delamination occurred, and mechanical properties were intermediate between those of the skin and core components alone. Dropped dart impact energy was controlled more by the skin layer than the core. In rigid PVC/GFR‐PVC co‐injected samples, impact energy was 2.5 times greater when GFR‐PVC was the core than when GFR‐PVC was the skin.     

Co‐injection molding of immiscible polymers: Skin‐core structure and adhesion studies

In this article, the microstructure and the adhesion developed in co‐injected specimens obtained with polypropylene (PP; core) and polystyrene (PS; skin) were studied as a function of process conditions and additives used. The study shows that the incorporation of low amounts of fillers such as Nanoclays and styrene‐ethylene‐butadiene‐styrene (SEBS) copolymer to the core material, working as compatibilizers, improves the adhesion at lower and higher polymer melt temperatures, respectively. The authors concluded as well that the use of such fillers, also improves the reproducibility of the process. The adhesion was assessed by shear tests using double lap shear specimens. A data acquisition system was attached to the mold to evaluate the pressure inside the cavity. Results of the in‐mold pressure profiles corresponded well when compared with MoldFlow predictions, and demonstrated that the adhesion of both materials is also related to their behavior and shrinkage inside the mold. POLYM. ENG. SCI., 2011. ©2011 Society of Plastics Engineers.     

Three‐dimensional simulation of multi‐material injection molding: Application to gas‐assisted and co‐injection molding

This paper presents an overview of the results obtained at the Industrial Materials Institute (IMI) on the numerical simulation of the gas‐assisted injection molding and co‐injection molding. For this work, the IMI's three‐dimensional (3D) finite element flow analysis code was used. Non‐Newtonian, non‐isothermal flow solutions are obtained by solving the momentum, mass and energy equations. Two additional transport equations are solved to track polymer/air and skin/core materials interfaces. Solutions are shown for different thin parts and then for thick three‐dimensional geometries. Different operating conditions are considered and the influence of various processing parameters is analyzed.     

Warpage of a large‐sized orthogonal stiffened plate produced by injection molding and injection compression molding

Rectangular plates of the size of 1800 × 600 × 12 mm³ and 1200 × 600 × 12 mm³ were selected for injection molding and injection compression molding, respectively, in order to investigate warpage characteristics of the large‐sized polymer plates with orthogonal stiffener. To determine the mold system and to reduce warpage of the specimen, numerical analyses for injection molding and injection compression molding were performed by using a commercial simulation code. Experiments were performed to verify the suggested mold system and warpage of the specimen. Relatively large warpage of the injection molded product was observed and small warpage of the injection compression molded product was generated. Compression force of the injection compression molding was only 6% of the clamp force of the injection molding. Warpage of the product was reduced significantly by using the injection compression molding. The injection compression molding will be used to substitute expensive and disused wood forms with inexpensive and recyclable polymer plates for concrete casting. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

退火对聚碳酸酯注塑制品力学及动态力学性能的影响

本文研究了聚碳酸酯（Lexan OQ2720）注塑制品退火后的力学及动态力学性能的变化。结果表明,制品的应力集中情况有明显改善,力学性能除断裂伸长率外都产生了较高提升,拉伸强度提高了14.86%,弯曲强度提高了12.7%,弯曲模量提高了21.27%,冲击强度提高了17.93%;动态力学分析结果表明,,注塑制品的内部存在应力。经退火后,注塑制品内部取向、缠结的分子链得到充分松弛,制品储能模量随温度的变化呈线性规律,内部链段的状态稳定,热变形温度得到了提高。而未退火试样的储能模量随温度变化起伏不定,内部链段的状态比较活跃。动态频率对制品中应力有一定响应能力,响应频率范围约为30-60Hz,随着频率扫描温度的升高,由于应力集中降低,频率对应力响应能力不断降低。     

The effect of molding conditions on mechanical and morphological properties at the interface of film insert injection molded polypropylene‐film/polypropylene matrix

An extensive study on the peel strength between a polypropylene (PP) film and PP substrate fabricated using film insert injection molding technique was carried out through a 180° peel test. Injection molding conditions such as barrel temperature, injection speed and holding pressure were varied to gauge their effects on the mechanical and morphological properties. Morphological observations were made at the film‐substrate interfacial regions by means of transmission electron microscopy (TEM). The injection molded products, with the films still attached, were subjected to bending and impact tests to determine if there is any relationship between film‐substrate adhesion and bulk properties. Observation of the load‐displacement curves during the peel test revealed three unique and interesting curves, corresponding to different peeling and film fracture mechanisms. Increases in injection speed, barrel temperature and holding pressure lead to increased bonding between the film and substrate surfaces. The enhancement of bonding between these two polymer surfaces could be attributed to polymer‐polymer interdiffusion. Substantiating evidence from TEM, which shows the fading of the interface as the bond strengthens, further boosts the accuracy of this assumption. The hope that the films could contribute to enhancing bulk properties has been diminished since the bending properties appeared to be similar with or without the film attached. Polym. Eng. Sci. 44:2327–2334, 2004. © 2004 Society of Plastics Engineers.     

Relationship between processing,microstructure, and mechanical properties of injection molded thermotropic LCP

A commercial thermotropic liquid crystalline polymer (LCP), Vectra A950, was injection molded into rectangular sheets of thickness ranging from 1 to 4 mm. By changing the thickness of the mold, the shear rate experienced by the TLCP melt in the mold could be varied. The 1‐mm test sample was highly anisotropic while that with larger thickness (4 mm) was less anisotropic. X‐ray diffraction profile at various depths for each of the test sample corresponded to the degree in the fiber orientation present in the test samples. The anisotropy can be described macroscopically by measuring the tensile strength and modulus in the longitudinal and transverse direction. The ratio between the longitudinal and transverse property decreases proportionally to the thickness of the test sample. This reduction corresponded to the reduction in the shear field as the thickness of the mold was increased. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1713–1718, 2003     

Effect of molding condition and pellets material on the weld property of injection molded jute/polylactic acid

Natural fibers such as jute fiber and biodegradable poly(lactic acid) (PLA) polymer are very good choices for environmental friendly material. Multi‐gate injection is often used to meet the demand of mass production of injection moldings, therefore weld line is inevitable. The presence of weld lines not only detracts from the surface quality but also significantly reduces the mechanical strength of injection‐molded parts. Although it is not always easy to completely eliminate weld lines, the weld strength could be improved through suitable adjustment of molding conditions such as melt temperature, mold temperature, hold pressure, injection speed, and so on. In this study, three kinds of pellets materials were prepared: long fiber pellets (LFT), the re‐compounding pellets (RP), and LFT50:RP50 hybrid mixtures (LFT/RP). Tensile test was carried out to investigate the effect of different pellets and holding pressures on the mechanical property of welded jute/PLA specimens. And the interfacial shear strength of non‐welded jute/PLA specimens was calculated with Kelly‐Tyson Formula. Fiber separation and fiber dispersion in RP became better than that of LFT which resulted in a better interfacial property. Weld strength of RP and hybrid LFT/RP specimens was improved by 43.34% and 16.46% than that of LFT specimen, respectively. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Physical–mechanical properties and morphological study on nylon‐6 recycling by injection molding

The effect of the multiple recycling of nylon‐6 by injection molding on its physical–mechanical properties and morphology was studied after each cycle of injection. These studies were made in order to know how many times it is possible to recycle the nylon‐6 without significant loss of the physical–mechanical properties. Optical and electronic microscopy were used to evaluated the morphology. Molecular weight changes were determinated by gel permeation chromatography (GPC). The nylon‐6 was recycled 10 times, until the eighth cycle the properties of the material did not suffered any change. Changes of 10–15% in the properties between nylon‐6 with 10 cycles of injection and virgin material were observed. An exception was the percentage of elongation that decreased 70% gradually until in the tenth cycle of injection. The results from GPC show that the molecular weight of nylon‐6 increased with recycling (M_w = 17% and M_n = 14%). With the reprocess was also observed the presence of gels. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 851–858, 2000     

Effect of the impact conditions on the mechanical properties of injection‐molded parts

This work focused on the study of the impact event on molded parts in the framework of automotive components. The influence of the impact conditions and processing parameters on the mechanical behavior of talc‐filled polypropylene specimens was analyzed. The specimens were lateral‐gate discs produced by injection molding, and the mechanical characterization was performed through instrumented falling weight impact tests concomitantly assisted with high‐speed videography. Results analyzed using the analysis of variance (ANOVA) method have shown that from the considered parameters, only the dart diameter and test temperature have significant influence on the falling weight impact properties. Higher dart diameter leads to higher peak force and peak energy results. Conversely, higher levels of test temperatures lead to lower values of peak force and peak energy. By means of high‐speed videography, a more brittle fracture was observed for experiments with higher levels of test velocity and dart diameter and lower levels of test temperature. The injection‐molding process conditions assessed in this study have an influence on the impact response of moldings, mainly on the deformation capabilities of the moldings. POLYM. ENG. SCI., 52:1845–1853, 2012. © 2012 Society of Plastics Engineers     

Thermoset injection molding dynamics and the distribution of cure in thermoset molded parts

A detailed characterization of a commercial-filled unsaturated polyester molding compound has been carried out to determine the kinetics of cure and the rheological behavior of the material at various temperatures and shear rates. Molding experiments were conducted in a 2 1/3 oz, 68 ton reciprocating screw injection molding machine, in conjunction with a simple rectangular cavity. The cavity and nozzle were equipped with pressure transducers to determine, the variation of pressure with position throughout the injection molding cycle. The injection speed was determined with the help of a position transducer. Finally, the moldings were analyzed to determine the distribution of cure states and tensile properties in the molding at various cure times. Significant differences have been observed. It is expected that studies of this type should be helpful in obtaining a better understanding of the thermoset injection molding process and the development of mathematical models to simulate this process.     

The mechanical properties of insert‐molded bimaterial composites

Bimaterial composite samples were constructed by injecting various polymers into a mold containing a fraction of a pre‐molded specimen. The resulting series composites were tested in tension. Breaking stresses were independent of fractional length. Conversely, both elongation to break and apparent stiffness varied with Although samples broke at or near the interface, adhesion was reasonably good, as indicated by transfer of material across interfaces.     

Effect of injection speed on the mechanical properties of isotactic polypropylene micro injection molded parts based on a nanoindentation test

Isotactic polypropylene micro parts were molded at different injection speeds by microinjection molding. The morphology and micro structure were characterized by a polarizing microscope, and the mechanical properties of differently structured layers were characterized by nanoindentation experiments. The influence of injection speed on the nanoindentation mechanical properties of each structural layer of the micro parts was analyzed. The results showed that the mechanical properties of different layers were different, the modulus and hardness of the position near the core layer were largest, and the modulus and hardness of the position near the skin were smallest. It is compelling that the modulus and hardness of each layer decreased first and then increased as the injection speed increased under a higher melt temperature (240 °C). Meanwhile, the opposite trend was observed at a lower melt temperature (220 °C). This phenomenon can be attributed to the competitive mechanism of the shear heat effect and the disorientation effect. In addition, injection speed had a greater influence on the nanoindentation mechanical properties in the perpendicular direction than in the flow direction. This work systematically explored the relationship between the microstructure and the local mechanical properties, which can provide new insights for microinjection molding design in the future. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47329.     

Morphology and mechanical properties of injection molded articles with weld-lines

The effect of weld-lines on the morphology and mechanical properties of injection molded articles made of neat poly(butylene terephthalate) (PBT) and glass fiber-reinforced PBT was investigated. The weld-line was introduced to a molded article by using a rectangularly shaped insert inside a mold cavity, and tensile specimens were prepared at various positions through the entire molded article. The weld-line position was further checked by a short-shot experiment. Although the maximum tensile stress for specimens of neat PBT with a weld-line is almost the same as that without a weld-line, the maximum tensile stress and the elongation at break for fiber-reinforced PBT with a weld-line were found to be about half of those without the weld-line. This is attributed to the fact that the fibers near the weld-lines are oriented parallel to the weld-line direction (or perpendicular to the tensile force direction) due to stretching flow. Finally, we compared experimental results of flow pattern and fiber orientations with numerical simulations. We found that the predictions of flow fronts and fiber orientations are in good agreement with experimental results.     

注压法和模压法对液体硅橡胶物理机械性能影响之比较

液体硅橡胶具有可成型形状复杂的制品、加工便捷高效、成本低效益好的特点研究发现,不同的成型方法对硫化胶性能几乎没有影响。     

Morphology and mechanical properties of injection‐molded ultrahigh molecular weight polyethylene/polypropylene blends and comparison with compression molding

The mechanical properties and morphology of UHMWPE/PP(80/20) blend molded by injection and compression‐molding were investigated comparatively. The results showed that the injection‐molded part had obviously higher Young's modulus and yield strength, and much lower elongation at break and impact strength, than compression‐molded one. A skin‐core structure was formed during injection molding in which UHMWPE particles elongated highly in the skin and the orientation was much weakened in the core. In the compression‐molded part, the phase morphology was isotropic from the skin to the core section. The difference in consolidation degree between two molded parts that the compression molded part consolidated better than the injection one was also clearly shown. In addition, compositional analysis revealed that there was more PP in the skin than core for the injection‐molded part, whereas opposite case occurred to the compression‐molded one. All these factors together accounted for the different behavior in mechanical properties for two molded parts. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of processing condition and carbon nanotube on mechanical properties of injection molded multi‐walled carbon nanotube/poly(methyl methacrylate) nanocomposites

In this work, multi‐walled carbon nanotubes (MWCNT) and poly(methyl methacrylate) (PMMA) pellets were compounded via corotating twin‐screw extruder. The produced MWCNT/PMMA nanocomposite pellets were injection molded. The effect of MWCNT concentration, injection melt temperature and holding pressure on mechanical properties of the nanocomposites were investigated. To examine the mechanical properties of the MWCNT/PMMA nanocomposites, tensile test, charpy impact test, and Rockwell hardness are considered as the outputs. Design of experiments (DoE) is done by full factorial method. The morphology of the nanocomposites was performed using scanning electron microscopy (SEM). The results revealed when MWCNT concentration are increased from 0 to 1.5 wt %, tensile strength and elongation at break were reduced about 30 and 40%, respectively, but a slight increase in hardness was observed. In addition, highest impact strength belongs to the nanocomposite with 1 wt % MWCNT. This study also shows that processing condition significantly influence on mechanical behavior of the injection molded nanocomposite. In maximum holding pressure (100 bar), the nanocomposites show highest tensile strength, elongation, impact strength and hardness. According to findings, melt temperature has a trifle effect on elongation, but it has a remarkable influence on tensile strength. In the case of impact strength, higher melt temperature is favorable. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43738.     

Effect of processing conditions on shrinkage in injection molding

A systematic study on the effect of processing conditions on mold shrinkage was undertaken for seven common thermoplastic polymers. It turned out that the holding pressure was always the key parameter. The effect of the melt temperature is slightly less important. Injection velocity and mold temperature do not show a general trend for all polymers. It was shown that at least for amorphous polymers a simple thermoelastic model could describe all experimental results. For semi-crystalline materials the model overpredicts shrinkage.