Effects of thermoplastic elastomer on the morphology and mechanical properties of glass fiber‐reinforced polycarbonate/acrylonitrile–butadiene–styrene

This article investigated the influence of thermoplastic elastomer like acrylonitrile–butadiene–styrene (ABS) high rubber powder (HRP), and ethylene methylacrylate (EMA) on the mechanical performances, flow ability, and morphology of glass fiber‐reinforced polycarbonate (PC)/ABS blends. Blending was carried out through a twin‐screw extruder, and all testing specimens were shaped by an injection molding machine. Experimental results showed that the toughening effect of EMA was more obvious than HRP due to fracture mechanism like crazing, shear yielding occurred in corporation with EMA. About 15 wt% glass‐fiber (GF) reinforcement and 6 wt% EMA toughening can get a balanced behavior among strength, stiffness, and toughness for superior performance of the polymer. POLYM. ENG. SCI., 59:E144–E151, 2019. © 2018 Society of Plastics Engineers     

Novel foaming method to fabricate microcellular injection molded polycarbonate parts using sodium chloride and active carbon as nucleating agents

Microcellular injection molding can fabricate lightweight, dimensionally stable plastic parts while using less material and energy. This article investigates a new process using water vapor as the physical blowing agent and comparing two kinds of nucleating agents, namely, cubic sodium chloride (NaCl) and non‐uniform active carbon (AC). The effects of different nucleating agents on the surface roughness, mechanical properties, and microstructure of solid and foamed parts were characterized. Compared with typical microcellular injection molded parts, water vapor‐foamed polycarbonate (PC)/NaCl had a smooth surface comparable to that of solid parts, whereas foamed PC/AC had desirable specific mechanical properties as well as an attractive average weight reduction of 16.4 wt%. Low density and non‐uniform AC particles, used as a nucleating agent and reinforcement, improved the microcellular structure. Based on PC molecular weight measurement, the melt processing and water vapor‐foaming processes did induce a slight amount of thermal degradation and hydrolytic degradation, respectively. POLYM. ENG. SCI., 55:1634–1642, 2015. © 2014 Society of Plastics Engineers     

Thin‐wall injection molding of polypropylene using molds with different laser‐induced periodic surface structures

In injection molding, high pressure is required to completely replicate the mold geometry, due to the viscosity of thermoplastic polymers, the reduced thickness of the cavity, and the low mold temperature. The reduction of the drag required to fill a thin‐wall injection molding cavity can be promoted by inducing the strong slip of the polymer melt over the mold surface, which occurs within the first monolayer of macromolecules adsorbed at the wall. In this work, the effects of different laser‐induced periodic surface structures (LIPSS) topographies on the reduction of the melt flow resistance of polypropylene were characterized. Ultrafast laser processing of the mold surface was used to manufacture nano‐scale ripples with different orientation and morphology. Moreover, the effects of those injection molding parameters that mostly affect the interaction between the mold surface and the molten polymer were evaluated. The effect of LIPSS on the slip of the polymer melt was modeled to understand the effect of the different treatments on the pressure required to fill the thin‐wall cavity. The results show that LIPPS can be used to treat injection mold surfaces to promote the onset of wall slip, thus reducing the injection pressure up to 13%. POLYM. ENG. SCI., 59:1889–1896, 2019. © 2019 Society of Plastics Engineers     

Analysis of crack phenomenon for injection‐molded screw using moldflow simulation

The screw for ice water filter machine was injection molded with acrylonitrile–butadiene–styrene (ABS)/polycarbonate (PC) [ABS/PC] alloy resin and its crack phenomenon after mechanical stress was analyzed by commercial Moldflow software. The cracked morphology and tensile properties of ABS/PC have been studied by scanning electron microscopy (SEM) and universal test machine (UTM). The injection pressure and the residual stress has been compared with two injection molding conditions as actual manufacturing and reduced injection flow rate. This analysis has found that residual stress is higher at actual manufacturing condition. SEM study reveals that in the micrographs taken on the surface of cracked sample ABS rubber domains tend to extremely align in the direction of mold flow. The combined data suggest that the majority of the crack comes from residual stress in final part originated from higher injection pressure during injection‐molding process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electron‐beam processing of nylon 6 and HNBR blends. Part II: development of high strength,heat‐ and oil‐resistant thermoplastic elastomers

The effects of electron‐beam irradiation on morphology, mechanical properties and on the heat and hot oil resistance of the thermoplastic elastomeric blend of 30:70 and 70:30, nylon 6 and hydrogenated nitrile rubber (HNBR) were investigated over the dose range 0–8 Mrad. The insoluble content of blends increased with increase in the radiation dose. The morphology of the blend was studied in scanning electron microscopy, with special reference to the effect of radiation prior to processing via injection molding. Irradiated pellets showed better mechanical properties after injection molding compared with irradiated sheets at low radiation dose. The observed differences in mechanical properties are explained on the basis of morphology of the blend. The blend properties were also found to have a strong dependence on nylon content. It was found that the blends rich in nylon had superior mechanical properties, hot oil and solvent resistance, whereas blends with higher HNBR content had better set and heat resistance. The effect of radiation on interaction in these blends was also evaluated and was found to induce possible inter‐chain crosslinking in the blends. Copyright © 2006 Society of Chemical Industry     

Morphology of gas‐assisted and conventional injection molded polycarbonate/polyethylene blend

The skin‐core structure of the gas‐assisted and conventional injection molded polycarbonate (PC)/polyethylene (PE) blend was investigated. The results indicated that both the size and the shape of the dispersed PC phase depended not only on the nature of PC/PE blend and molding parameters, but also on its location in the parts. Although the gas‐assisted injection molding (GAIM) parts and conventional injection molding (CIM) part have the similar skin‐core structure, the morphology evolution of PC phase in the GAIM moldings and the CIM moldings showed completely different characteristics. In the section perpendicular to the melt flow direction, the morphology of the GAIM moldings included five layers, skin intermediate layer, subskin, core layer, core intermediate layer as well as gas channel intermediate layer, according to the degree of deformation. PC phase changed severely in the core layer of GAIM moldings, as well as in the subskin of CIM moldings. In GAIM parts, PC phase in the core layer of the nongate end changed far more intensely and aligned much orderly than that in the gate end. The morphology of PC phase in the GAIM part molded with higher gas pressure changed more severe than that in the GAIM part molded with lower gas pressure. In a word, PC phase showed more obvious fibrillation in the GAIM moldings than that in the CIM moldings. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3069–3077, 2006     

Influencing hardness and wear during the dynamic tempered microinjection molding process by considering isothermal holding time

For semicrystalline thermoplastic parts it is well known that increasing isothermal holding temperature can affect inner component properties, respectively, crystalline structure (e.g., morphology, degree of crystallization, crystal modification, etc.) and, therefore, resulting global component properties such as hardness and wear. Nevertheless, in literature there is no explicit focus on the effect of isothermal holding time during dynamically tempered injection molding process. In this article, semicrystalline microcomponents have been injection molded by varying isothermal holding time within the material's crystallization temperature area. As materials, POM‐C, as a material with relatively high crystallization kinetic, and PA 12, as a material with medium crystallization kinetic, were used. To evaluate the effects on hardness and wear, nanoindentation measurements as well as pin‐on‐disc wear tests were performed. Results show that for fast crystallizing POM‐C an isothermal holding step has no significant influence on inner component and resulting global component properties. For slower crystallizing PA 12, however, the morphology and the degree of crystallization could be influenced and, as a result, hardness could be increased by 21% while wear could be reduced by 30%. POLYM. ENG. SCI., 57:121–128, 2017. © 2016 Society of Plastics Engineers     

Evaluation of molecular orientation in injection molded parts with microscale features by Raman spectroscopy

Molecular orientation of polycarbonate (PC) in injection‐molded parts with microscale features was characterized by means of polarized Raman spectroscopy, and the relationship between microstructure and replication was discussed. The microscale feature size of continuous v‐groove was 20 μm in depth and 50 μm in width. PC injection‐molded parts were molded with various molding conditions. The molecular orientation distribution along flow direction on the cross‐section of molding parts were evaluated by the intensity ratio of the bands at 635 to 703 cm^?1 (I₆₃₅/I₇₀₃) in the Raman spectra. Molecular orientation along the flow direction inside the v‐groove was higher than that of the core and the opposite surface region. In particular, the highest molecular orientation was at the surface of the v‐groove. Among the injection molding conditions, the mold temperature showed significant effect on the molecular orientation and replication. Higher mold temperature caused high replication and low molecular orientation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Water‐assisted injection molding of thermoplastic materials: Effects of processing parameters

The objective of this study was to experimentally investigate the effects of various processing parameters on the water‐assisted injection molding of thermoplastic materials. Experiments were carried out on a lab‐developed water‐assisted injection molding system, which included a water pump, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. Two types of water injection pins designs were proposed to mold the parts. After molding, the lengths of water penetration in molded parts were measured. The effects of different processing parameters on the lengths of water penetration were determined. It was found that the shrinkage rate and the viscosity of the polymeric materials, and the void shapes of the hollowed cores mainly determined the water‐penetration lengths in molded products. In addition, a comparison has been made between the parts molded by water assisted injection molding and gas‐assisted injection molding. It was found that water‐assisted injection molded parts exhibit less uniform void sizes along the water channel. The cycle time for water‐assisted injection molded parts was shorter than that of conventional injection molded parts and gas‐assisted injection molded parts.     

The occurrence of surface roughness in gas assist injection molded nylon composites

Gas assist injection molding has increasingly become an important industrial process because of its tremendous flexibility in the design and manufacture of plastic parts. However, there are some unsolved problems that limit the overall success of this technique. The purpose of this report was to study the surface roughness phenomenon occurring in gas assist injection molded thermoplastic composities. The materials used were 15 % and 35% glass‐fiber filled nylon‐6 composites. Experiments were carried out on an 80‐ton injection molding machine equipped with a high‐pressure nitrogen‐gas injection unit. Two “float‐shape” axisymmetric cavities were used. After molding, the surface quality of molded parts was measured by a roughness meter. Various processing variables were studied in terms of their influence on formation of surface roughness: melt temperature, mold temperature, melt filling speed, short‐shot size, gas pressure, and gas injection delay time. Scanning electronic microscopy was also employed to characterize the composites. It was found that the surface roughness results mainly from the exposure of glass fiber in the matrix. The jetting and irregular flows of the polymer melt during the filling process might be factors causing the fiber exposure.     

Rheological and mechanical behavior of long‐polymer‐fiber reinforced thermoplastic pellets

Polymer–polymer materials consist of a thermoplastic matrix and a thermoplastic reinforcement. Recent research activities concentrate on the manufacturing of semi‐finished polymer–polymer materials in other shapes than the commercially available tapes and sheets. In particular, a pellet‐like form provides the possibility of processing the polymer–polymer material by injection and compression molding. Nevertheless, the thermoplastic reinforcement is vulnerable to excessive heat and the processing usually needs special attention. The current study investigates the processing of long‐polymer‐fiber reinforced thermoplastic pellets, namely polypropylene‐polyethylene terephthalate and a single‐polymer polyethylene terephthalate, by extrusion for subsequent compression molding applications. The flow characteristics of the material as well as the preservation of the polymer reinforcement can be handled by accurate temperature control. The tensile and impact properties decrease with increasing process temperature though. Moreover, the results prove that the use of a common long‐fiber reinforced thermoplastic process chain is applicable to the newly developed polymer–polymer material. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39716.     

Fluid–structure interaction analysis on the film wrinkling problem of a film insert molded part

Back‐injection of polymeric liquid to preformed films, also known as film insert molding (FIM), provides the surface quality of polymeric parts. The back‐injection material is responsible for mechanical and thermal properties of the part, especially such as stiffness and thermal expansion. In the back‐injection molding it is important to ensure that the inserted films are not wrinkled by the injection of molten polymers. In this study, FIM was carried out with utilizing polycarbonate/acrylonitrile butadiene styrene (PC/ABS) alloy and polymethyl methacrylate/acrylonitrile butadiene styrene (PMMA/ABS) film. The wrinkling of films was observed by the atomic force microscope (AFM). Numerical simulations were performed to understand the mechanism of the film wrinkling and optimize the processing conditions of FIM for high precision parts by using commercial packages including Hypermesh?, Moldflow?, and COMSOL?. A critical shear rate for the film wrinkling of a center garnish part was determined based on the deformation energy of plate. It was found that the critical shear rate calculated numerically was in good agreement with that of the film insert molded parts. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Electrical resistivity of polycarbonate/multiwalled carbon nanotube composites under varying injection molding conditions

Multiwalled carbon nanotube (MWCNT)‐filled polycarbonate composites were prepared by a corotating intermeshing twin‐screw extruder. The surface resistivities of compression‐ and injection‐molded specimens were quite different, the difference ranging from 10³ to 10⁷ Ω/sq at varying MWCNT concentrations. The surface resistivity of the injection‐molded specimen at 2 wt % loading varied up to 10⁵ Ω/sq in the specimen thickness direction and up 10⁴ Ω/sq in the polymer flow direction with respect to the gate. The difference in surface resistivity with the positions of injection‐molded specimen was confirmed with the morphology, which showed the difference in MWCNT number density (numbers/surface area). There was no significant effect on surface resistivity with injection pressure, holding pressure, and molding temperature. The specimens prepared at the injection speed of 13 mm/s showed surface resistivities 10³–10⁴ Ω/sq depending on the positions, which was comparable with the compression‐molded specimens, which had a surface resistivity of 10³ Ω/sq. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Gold nanoparticle layers from multi‐step adsorption immobilised on a polymer surface during injection molding

Functional nanoparticles exhibit, e.g., a chemical functionality. For their use, a reliable immobilisation is often required. Here, a method is described, how those nanoparticles can be immobilised on a thermoplastic surface using melt processing. Gold nanoparticles (AuNP) are assembled in a layer on a substrate by adsorption. The degree of coverage can be controlled by repeating the adsorption process. During each adsorption step, the particles were arranged on the surface as chain‐like aggregates with close particle–particle contacts, rather than as isolated particles. The degree of area coverage on the substrate surface was up to 70%. The AuNP layers were transferred onto the surfaces of polycarbonate (PC) sheets by injection molding. The AuNP were partly embedded by the thermoplastic polymer and in this way permanently immobilised on the part surface. The reduction of methyl orange demonstrated the accessibility of the gold surface for small molecules. Furthermore, the fabrication of bactericide surfaces, sensor surfaces, all using AuNP immobilised on a thermoplastic part surface may become possible. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43608.     

Linear viscoelastic and morphological description of multiphase systems affected by processing parameters

Influence of processing methods, in terms of comparing compression and injection moldings, on the rheological behavior of polycarbonate (PC)/acrylonitrile‐butadiene‐styrene (ABS) blends and PC/ABS/glass fibers composites is presented. Blend compositions and fiber content are considered as material variables. For blends, the effect of the processing route on the viscoelastic functions is evident only for low shearing frequencies. Injection molding created morphology with cocontinuous character, while compression molded blends have “relaxed” structure, where dispersed phase domains are several times larger than in injection molded ones. The glass fiber reinforcement led to the significant differences in viscoelastic properties of composites processed by injection and compression molding. Injected composites have both moduli always higher than compression molded. Also, fiber lengths are reduced more for compressing molding. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Properties enhancement of short glass fiber‐reinforced thermoplastics via sandwich injection molding

This article demonstrates using sandwich injection molding in order to improve the mechanical properties of short glass fiber‐reinforced thermoplastic parts by investigating the effect of fiber orientation, phase separation, and fiber attrition compared to conventional injection molding. In the present case, the effect of short glass fiber content (varying from 0–40 wt%) within the skin and core materials were studied. The results show that the mechanical properties strongly depend not only on the fiber concentration, but also on the fiber orientation and the fiber length distribution inside the injection‐molded part. Slight discrepancies in the findings can be assumed to be due to fiber breakage occurring during the mode of processing. POLYM. COMPOS., 26:823–831, 2005. © 2005 Society of Plastics Engineers     

The property of polycarbonate/acrylonitrile butadiene styrene‐based conductive composites filled by nickel‐coated carbon fiber and nickel–graphite powder

The filled conductive composites were prepared with a polycarbonate/acrylonitrile butadiene styrene matrix and both nickel‐coated carbon fiber (NiCF) and nickel–graphite powder (NCG) as fillers by using injection molding and injection‐compression molding. The effect of the NiCF content, NCG content, coupling agent, and molding methods on the properties of composites was studied. The results showed that the conductivity of the composites increased with raising the NiCF content and NCG content. NiCF treated with silane coupling agent could further improve the conductivity of the composites without any significant change in mechanical properties. Furthermore, compared with injection molding, the composites prepared by injection‐compression molding possessed better conductivity. POLYM. COMPOS., 38:157–163, 2017. © 2015 Society of Plastics Engineers     

The effect of γ‐Irradiation and reactive extrusion on the structure and properties of polycarbonate and starch blends: A work oriented to the recycling of thermoplastic wastes

Polymer materials with improved properties can be obtained through polymer blends. As a polymer mixture is generally immiscible and incompatible, it is necessary to develop new methods to improve the interfacial adhesion. In this study, polycarbonate‐based extruded thermoplastic were developed by blending polycarbonate with thermoplastic starch using extensive process engineering based on structure–property correlations. Starch was destructurized and plasticized followed by melt‐blending with polycarbonate. The optimal conditions for processing of the thermoplastics blends were found to be 230°C, 2 min of processing time, and 3–6 wt % of glycerol. The effect of γ‐irradiation on the fabrication of the blend was studied. Changes in structure, morphology, and properties resulting from γ‐exposure in the range 0–150 kGy were investigated. Electron spin resonance results revealed that numerous radicals remained trapped in the materials after irradiation even after a long time enabling reactions between starch and polycarbonate. Results obtained from tensile test, differential scanning calorimetry, and dynamic mechanical analysis revealed the relatively good affinity between the two components after blending in a micro‐extruder. Irradiated blends are thermally more stable than those non‐irradiated. Mechanical tests also showed that the efficiency of the irradiation depended greatly on the dose applied to the initial materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A new microcellular injection molding process for polycarbonate using water as the physical blowing agent

This article presents a new process for producing microcellular injection molded plastic parts using water as the physical blowing agent and micro‐scaled particles as the cell nucleating agents. Distilled water with dissolved salt were fed through the hopper of an injection molding machine at a preset rate and mixed with polycarbonate (PC) in the machine barrel. Microcellular PC tensile bars were then injection molded with different shot volumes, water/salt solution feed rates, and salt concentrations. Tiny salt crystals of 10–20 μm recrystallized during molding acted as nucleating agents in the PC foamed parts. The surface roughness, mechanical properties, and microstructure of the solid and foamed parts were measured and compared with microcellular injection molded parts using supercritical fluid (SCF) nitrogen as the physical blowing agent. At a similar weight reduction of about 10%, the water foamed PC parts have a smooth surface comparable to that of solid injection molded parts. They also possess similar, if not better, mechanical properties compared to SCF nitrogen foamed PC parts. Without the nucleating agent, PC/water foamed parts exhibit much larger and fewer bubbles within the molded parts. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Processing and physical properties of native grass-reinforced biocomposites

Big blue stem grass fiber-reinforced high density polyethylene powder biocomposites were fabricated using two separate processing schemes: (1) by compounding biofiber with the thermoplastic powder in an extruder and subsequently injection molding the extrusion pellets and (2) by combining biofiber and the powder thermoplastic powder using a modified sheet molding compounding (SMC) line and subsequently compression molding the sheet material. The physical properties including storage modulus, heat deflection temperature (HDT), notched Izod impact strength, and morphology were evaluated with dynamic mechanical analysis, Izod impact strength measurement, and microscopy observation. It was found that compression-molded specimens achieved similar modulus values to injection molded specimens for grass-reinforced high density polyethylene (HDPE) composites. The stiffness of the compression-molded specimens is related to the consolidation state of the samples, which depends on compression molding conditions such as temperature, pressure, and mold type. Compression-molded specimens exhibited a higher HDT and notched Izod impact strength compared to injection-molded samples. Grass fiber-reinforced cellulose acetate butyrate (CAB) biocomposites made with SMC processing had similar physical properties with grass fiber-reinforced HDPE composites, which indicates that natural fiber-reinforced CAB biocomposites have the potential to replace polyolefin-based composites for automotive applications. POLYM. ENG. SCI. 47:969–976, 2007. © 2007 Society of Plastics Engineers.