Compatibilizing effect of maleated polypropylene on the mechanical properties and morphology of injection molded polyamide 6/polypropylene/organoclay nanocomposites

Polyamide 6/polypropylene (PA6/PP=70/30 parts) blends containing 4 phr (parts per hundred resin) of organophilic modified montmorillonite (organoclay) were prepared using twin screw extruder followed by injection molding. Maleated polypropylene (MAH-g-PP) was used to compatibilize the blend system. The mechanical properties of PA6/PP nanocomposites were studied through tensile and flexural tests. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to assess the fracture surface morphology and the dispersion of the organoclay, respectively. X-ray diffraction (XRD) was used to characterize the formation of nanocomposites. The thermal properties were characterized by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The dynamic mechanical properties of PA6/PP nanocomposites were analyzed by using dynamic mechanical thermal analyzer (DMTA). The strength and stiffness of PA6/PP nanocomposites were improved significantly in the presence of MAH-g-PP. This has been attributed to the synergistic effect of organoclay and MAH-g-PP. The MAH-g-PP compatibilized PA6/PP nanocomposites showed a homogeneous morphology supporting the compatibility improvement between PA6, PP and organoclay. TEM and XRD results revealed the formation of nanocomposites as the organoclay was intercalated and exfoliated. A possible chemical interaction between PA6, PP, organophilic modified montmorillonite and MAH-g-PP was proposed based on the experimental work.     

Interfacial influence on mechanical properties of polypropylene/polypropylene‐grafted silica nanocomposites

Three types of polypropylene‐grafted silica (PGS‐2 K, PGS‐8 K and PGS‐30 K) with different grafting chain lengths were prepared. After melt‐blending PGS with polypropylene (PP), we studied the PP/PGS interface properties and the influence of PP/PGS interfaces on mechanical properties of nanocomposites. The strong matrix/particle interface was observed in PP/PGS‐30 K nanocomposites with 5 wt % particle loading as evidenced by 2.5 °C increased glass transition temperature (T_g) compared with neat PP, whereas the weak matrix/particle interface was observed in PP/PGS‐2 K nanocomposites with decreased T_g. The variations in the matrix/particle interfacial strength lead to a transition in the yield stress of nanocomposites. Compared with the unfilled PP, the yield stress of the PP/PGS‐2 K nanocomposites is decreased by 0.7 MPa, and the yield stress of the PP/PGS‐30 K nanocomposites is enhanced by 1.4 MPa. In addition, benefiting from good dispersion, the PP/PGS‐masterbatch nanocomposites with a strong matrix/particle interface not only exhibit increased Young's modulus and yield stress, but also the strain at break remains in line with the unfilled PP, which is in contrast to the conventional wisdom that the gain in modulus and strength must be at the expense of the decreased break strain. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45887.     

The effect of organoclay on the mechanical properties and morphology of injection‐molded polyamide 6/polypropylene nanocomposites

Nanocomposites containing a thermoplastic blend and organophilic layered clay (organoclay) were produced by melt compounding. The blend composition was kept constant [polyamide 6 (PA6) 70 wt % + polypropylene (PP) 30 wt %], whereas the organoclay content was varied between 0 and 10 wt %. The mechanical properties of the nanocomposites were determined on injection‐molded specimens in both tensile and flexural loading. Highest strength values were observed at an organoclay content of 4 wt % for the blends. The flexural strength was superior to the tensile one, which was traced to the effect of the molding‐induced skin‐core structure. Increasing organoclay amount resulted in severe material embrittlement reflected in a drop of both strength and strain values. The morphology of the nanocomposites was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy‐dispersion X‐ray analysis (EDX), and X‐ray diffraction (XRD). It was established that the organoclay is well dispersed (exfoliated) and preferentially embedded in the PA6 phase. Further, the exfoliation degree of the organoclay decreased with increasing organoclay content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 175–189, 2004     

Effect of crystallization and interface formation mechanism on mechanical properties of film‐insert injection‐molded poly(propylene) (PP) film/PP substrate

A previous study has shown that the adhesion between the film and substrate of film‐insert injection‐molded poly(propylene) (PP) film/PP substrate was evident with the increases in barrel temperature and injection holding pressure. In this second part of the research work, the crystallinity at the interfacial region (i.e., region between the film and the injected substrate) was extensively studied using FTIR imaging, polarized light microscopy, and DSC in an attempt to determine the level of influence that crystallinity has on the interface and bulk mechanical properties. Consequently, a more thorough and clearer picture of the influence of the inserted film on the interfacial crystallinity and subsequently the substrate mechanical properties, such as peel strength and impact strength, has been revealed. The initial proposition that crystallinity could enhance film–substrate interfacial bonding has been confirmed, judging from the higher peel strength with increasing crystallinity at the interfacial region. Nevertheless, the change in crystallinity was not only confined to the interfacial region. With the film acting as heat‐transfer inhibitor between the injected resin and the mold wall, the total crystal structure of the substrate was substantially altered, which subsequently affected the bulk mechanical properties. The lower impact strength of film‐insert injection‐molded samples compared to that of samples without film inserts provided evidence of how the film could impart inferior properties to the substrate. The difference in cooling rate between the substrate and film might also cause other defects such as warpage and/or residual stress build‐up within the product. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 294–301, 2005     

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     

Mechanical properties and morphological behavior of calcium carbonate‐filled polypropylene in dynamic injection molding

A custom‐made electromagnetic dynamic injection molding machine was adopted to study the mechanical properties and morphological behavior of calcium carbonate‐filled polypropylene (PP) in a dynamic injection molding process. The influence of vibration amplitude and frequency on the mechanical properties and morphological behavior of samples was investigated using tensile tests, notched Izod impact tests, differential scanning calorimetry, and scanning electronic microscopy. The tensile stress and the impact stress for all samples investigated were found to increase in a nonlinear manner with increasing vibration amplitude and frequency. The tensile stress reached a maximum value at about 8 Hz and 0.15 mm for neat PP and PP filled with 3, 20, and 30 wt% CaCO₃. For PP filled with 40 wt% CaCO₃, the tensile stress reached a maximum value at about 12 Hz and 0.2 mm. The impact stress reached a maximum value at about 12 Hz. From DSC experiments it was shown that the melting temperature slightly increased, but no new polymeric crystalline peak appeared under the vibration force field. The CaCO₃ particles were diffused easily and distributed evenly in the PP melt under the vibration force field, so it is very useful in improving the quality of injection products. Copyright © 2006 Society of Chemical Industry     

Morphology and mechanical properties of direct injection molded polypropylene/thermotropic copolyester blends

Blends of two grades of polypropylene (PP) with thermotropic copolyester (Rodrun) contents of up to 40% were obtained by direct injection molding at different processing temperatures. In the skin of the molded specimens rather long fibers were seen in blends with low‐viscosity PP, whereas sheets were found when the high‐viscosity PP was the matrix. In the core, the viscosity of the matrix played a more relevant role than the viscosity ratio on the orientation level of the dispersed Rodrun phase. The better mechanical properties of the blends with the low viscosity PP are attributed to the morphology change of the dispersed phase from sheets to fibers when the viscosity of the matrix decreased.     

The stress relaxation behavior and mechanical properties of polypropylene and polypropylene/CaCO3 in mechanical vibration injection molding

The influence of vibration pressure and frequency on the mechanical properties and stress‐relaxation was investigated via stress‐relaxation test and tensile test. First, it had been observed in the tensile test that the tensile fracture elongation reached the maximum at 20 Hz for polypropylene (PP) and 15 Hz for polypropylene/calcium carbonate (PP/CaCO₃), respectively. With the increasing vibration pressure, the tensile fracture elongation would decrease. Second, the dynamic mechanic analysis has been used to test loss angle tangent value of the material. After the dynamic mechanic analysis, the simples have been installed in the universal tensile testing machine which applies the 2% strain on the simples. From these experiments, it has been discovered that the trend of the changes of stress‐relaxation is similar with the trend of the changes of loss angle tangent value. When the vibration frequency reaches the 20 Hz for PP and 15 Hz for PP/CaCO₃, the stress‐relaxation is larger than that of other materials prepared at the same pressure (10 Mpa); meanwhile, the stress‐relaxation of these materials, which has been prepared at the same frequency (10 Hz), decreases with the increasing vibration pressure. According to above tests, it is also very useful to improve the stress relaxation properties via changing the condition of the vibration field. POLYM. ENG. SCI., 2009. © 2008 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     

The impact of polypropylene‐graft‐maleic anhydride on the crystallization and dynamic mechanical properties of isotactic polypropylene

Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to identify the mechanisms that lead to differences in the mechanical behavior of formulations of polypropylene blended with maleated polypropylene (MAPP) copolymers. MAPP lowered the melting temperature of PP indicating that less stable crystals were formed possibly because of cocrystallization of PP and MAPP. Crystallization kinetics revealed that copolymers do not change the rate of crystal growth, but may retard nucleation leading to a more spherulitic morphology. The dynamic storage modulus slightly increased in the glassy region with the small addition amounts of MAPP, while mechanical dampening systematically decreased with MAPP addition. An analysis of the viscoelastic behavior did not reveal any real differences in molecular coupling around the β‐transition of PP with the addition of the MAPP copolymer. At low addition levels, MAPP does not appear to have a significant impact on the viscoelastic properties of the polymer blend. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of orientation on the mechanical properties of injection molded polystyrene

The deformation and fracture behavior of injection molded plaques have been determined, and the results interpreted in terms of the effect of molecular orientation on the crazing and shear yielding behavior. The molecular orientation was characterized by optical birefringence. A range of injection molding conditions and two mold thicknesses were Used and this resulted in a large variation in the molecular orientation, particularly through the sheet thickness. Tensile tests were made on samples cut at different angles to the injection molding direction. The moldings are considered to consist of a composite of layers of material with different orientation, and the properties of the samples cut from the molding are analyzed in terms of the properties of each layer. Results from material oriented unidirectionally by hot drawing have been used to predict the composite properties, and good agreement has been obtained.     

Co‐injection molding: Effect of processing on material distribution and mechanical properties of a sandwich molded plate

The effect of molding parameters on material distribution and mechanical properties of co‐injection molded plates has been studied using experimental design. The plates were molded with a polyamide 6 (PA 6) as skin and a 20% glass fiber‐reinforced polybutyleneterephtalate (PBTP) as core. Five molding parameters—injection velocity, mold temperature, skin and core temperature, and core content—were varied in two levels. The statistical analysis of the results showed that three parameters—Injection velocity, core temperature, and core content—were the most significant in affecting skin/core distribution. A high core temperature was the most significant variable promoting a constant core thickness, while core content was the most significant factor influencing a breakthrough of the core. Mechanical properties, such as flexural and impact strength showed a high correlation with the skin/core distribution. The slight increase in falling weight impact strength of the sandwich molded plates, compared to similar plates molded from PBTP only, could be explained from the failure process, which initiates in the brittle core and propagates through the ductile skins.     

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     

Electrical and morphological properties of microinjection molded polypropylene/carbon nanocomposites

A series of different carbon (carbon black, carbon nanotubes, and graphite nanoplatelets) filled polypropylene nanocomposites were prepared by melt blending, then followed by compression molding or microinjection molding (µIM). Direct current electrical conductivity measurements and melt rheology tests were utilized to detect the percolated structure for compression molded polypropylene/carbon nanocomposites. For µIM, a rectangular mold insert which has a three‐step decrease in thickness along the flow direction was adopted to study the effect of abrupt changes in mold geometry on the electrical and morphological properties of subsequent micromoldings (µ‐moldings). Results indicated that the µ‐moldings exhibited a higher percolation threshold when compared with their compression molded counterparts. This is largely due to the severe shearing conditions that prevail in the µIM process. The morphology of µ‐moldings containing different carbon fillers was examined using scanning electron microscopy. The development of corresponding microstructure is found to be strongly dependent on the types of carbon fillers used in µIM, which is crucial to the enhancement of electrical conductivity for the resulting µ‐moldings. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45462.     

热压成型和注塑成型CF/PP复合材料的力学性能对比

通过热压成型和注塑成型2种不同加工方法制备了碳纤维(CF)/聚丙烯(PP)导电复合材料,对比了2种复合材料的力学性能,结果表明注塑成型的CF/PP具有较高的拉伸强度和弹性模量。结合扫描电子显微镜观察,分析了这2种加工方法对CF/PP复合材料的微观结构和力学性能的影响。     

Shrinkage behavior and mechanical performances of injection molded polypropylene/talc composites

In this research, the influences of adding talc mineral particles of 10 μm particle size on the shrinkage and the mechanical properties of injection molded polypropylene (PP)/talc composites were investigated. PP has a crystalline molecular structure and hence it possesses nonisotropic shrinkage along and across the flow directions. Addition of the talc mineral filler to PP induced an isotropic shrinkage in the molded part because of the nonisotropic shape of talc particles. The results of experiments indicated that the maximum flexural strength, maximum impact strength, and isotropic shrinkage were achieved by adding 10, 20, and 30 by weight percent of talc respectively. By incorporating of 10 wt% of talc particles into the PP matrix, the tensile strength was hardly affected but the occurrence of cold drawing phenomena in the tensile test was hindered considerably. The flake‐shape structure of talc filler played an important role in determining the molded part shrinkage and mechanical properties. POLYM. ENG. SCI., 47:2124–2128, 2007. © 2007 Society of Plastics Engineers     

The effect of annealing at 135° on the mechanical properties of injection molded high density polyethylene-polypropylene blends

The effect of annealing at 135°C for 5 hours on the tensile properties of mechanically mixed and then injection molded high density polyethylene (HDPE) and polypropylene (PP) blends has been investigated. Both the tangent elastic modulus and the tensile strength at yield exhibit a non-linear behavior versus blend composition with a minimum of properties typical for incompatible blends. Annealing substantially improves mechanical properties of pure components and blends (20 percent increase in the yield strength of pure components and blends and the modulus of pure components, and ～40 percent increase in the modulus of 50/50 blends) but the property behavior versus composition is still nonlinear. Scanning electron microscopy studies of fracture surfaces of blends seems to indicate some improvement in bonding between phases as a result of annealing, Both the elastic modulus and yield strength fit extremely well to the modified “rule of mixtures” equation in the general form: M_b = M_PEφ_PE + M_PPφ_PP + ΔM_PE/PPφ_PEφ_PP where M_b is the blend property, M_PE and M_PP are properties of pure PE and PP components, φ_PE and φ_PP are weight fractions of PE and PP, and ΔM_PE/PP is the interaction term being a measure of the deviation from simple additivity.     

Shear‐induced fibrillation and resultant mechanical properties of injection‐molded polyamide 1010/isotactic polypropylene blends

It is feasible to control the phase morphology and orientation for immiscible polymer blends to manipulate their properties. In this paper, the blend of polyamide 1010 (PA1010) and isotactic polypropylene (iPP) (mainly at a fixed ratio of PA1010/iPP = 80/20) was used as an example to demonstrate the effect of shear on the morphology and resultant mechanical properties. After being melt blended, the injection‐molded bars were prepared via a dynamic packing equipment to impose a prolonged shearing on the melts during the solidification stage. By controlling the shear time, the structure evolution and morphological development of the blends can be well controlled. Mechanical measurement of the molded bar showed a dramatically improved tensile property and impact strength with increasing shear time. Morphological examination revealed that the iPP droplets are elongated and become thin fibrils along the shear direction with increasing shear time. The shear‐induced fibrillation, instead of orientation, is believed to be responsible for the largely improved properties of the blend, particularly for the impact strength. The toughening mechanism is discussed based on the combined effect of hindrance of crack propagation and the transferring and bearing of the load due to the existence of the fibrils. This was further proved by changing the blending ratio and using low molecular weight iPP. Finally, we propose a concept for designing blending materials with good comprehensive properties. Copyright © 2011 Society of Chemical Industry     

Compounding and injection molding of polybutene‐1/polypropylene blends

The effect of shear‐controlled orientation injection molding (SCORIM) was investigated for polybutene‐1/polypropylene blends. This article reports on the methods and processing conditions used for blending and injection molding. The properties of SCORIM moldings are compared with those of conventional moldings. SCORIM is based on the application of specific macroscopic shears to a solidifying melt. The multiple shear action enhances molecular alignment. The moldings were investigated with mechanical tests, differential scanning calorimetry studies, and polarized light microscopy. The application of SCORIM improved Young's modulus and the ultimate tensile strength. The gain in stiffness was greater for higher polybutene‐1 content blends. A drastic decrease in the strain at break and toughness was observed in SCORIM moldings. The enhanced molecular orientation of SCORIM moldings resulted in a featureless appearance of the morphology. Interfacial features due to segregation were visible in the micrographs of SCORIM moldings. Both conventional and SCORIM moldings exhibited form I′ in polybutene‐1. This article explains the relationship between the mechanical properties and micromorphologies. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 806–813, 2003     

Tailoring microstructure and mechanical properties of injection molded isotactic–polypropylene via high temperature preshear

In this work, isotactic–polypropylene (iPP) specimens were prepared by a modified injection molding machine, in which high temperature preshear (HTPS) can be imposed on the molten polymer during the plasticizing stage. The effect of HTPS on the microstructure and mechanical property of iPP was investigated. It was found that spherulite size in core region of iPP part decreased steadily with the increasing HTPS duration, indicating that HTPS could substantially enhance iPP nucleation. Moreover, β ‐iPP formation correlated strongly with HTPS duration. That is, in the absence of HTPS, β ‐iPP existed only in intermediate region; with moderate HTPS duration, β ‐iPP could be unexpectedly formed in core region; however, long HTPS duration inhibited β ‐iPP formation in both intermediate region and core region. Based on the relationship between β ‐iPP formation and HTPS duration, metastable nuclei, instead of α ‐row nuclei, were proposed to be responsible for the development of β ‐iPP. Notched Izod impact test showed that moderate HTPS duration enhance the impact strength of injection molded iPP by decreasing the thickness of shear region and elevating β ‐iPP crystallinity in core region. Dynamic mechanical test indicated that with the increase of HTPS duration, the storage modulus of injection‐molded iPP improves drastically. POLYM. ENG. SCI., 55:2714–2721, 2015. © 2015 Society of Plastics Engineers