Improved mechanical properties and structure of PP/nano‐CaCO3 blends prepared by low‐frequency vibration injection molding

BACKGROUD: Melt vibration technology was used to prepare injection samples of polypropylene (PP)/nano‐CaCO₃ blends. It is well known that nano‐CaCO₃ particles are easy to agglomerate owing to their large surface energy. Improving the distribution of nano‐CaCO₃ particles in PP/nano‐CaCO₃ blends is very important for enhancing the mechanical properties. In this work, low‐frequency vibration was imposed on the process of injection molding of PP/nano‐CaCO₃ blends. The aim of importing a vibration field was to change the crystal structure of PP as we studied previously and improve the distribution of nano‐CaCO₃ particles. Furthermore, the mechanical properties were improved. RESULTS: Through melt vibration, the mechanical properties of PP/nano‐CaCO₃ samples were improved significantly. Compared with conventional injection molding, the enhancement of the tensile strength and impact strength of the samples molded by vibration injection molding was 17.68 and 175.96%, respectively. According to scanning electron microscopy, wide‐angle X‐ray diffraction and differential scanning calorimetry measurements, it was found that a much better dispersion of nano‐CaCO₃ in samples was achieved by vibration injection molding. Moreover, the crystal structure of PP in PP/CaCO₃ vibration samples changed. The γ crystal form was achieved at the shear layer of vibration samples. Moreover, the degree of crystallinity of PP in vibration samples increased 6% compared with conventional samples. CONCLUSION: Concerning the microstructure, melt vibration could effectively change the crystal structure and increase the degree of crystallinity of PP besides improving the distribution of nano‐CaCO₃ particles. Concerning the macrostructure, melt vibration could enhance the mechanical properties. The improvement of mechanical properties of PP/nano‐CaCO₃ blends prepared by low‐frequency vibration injection molding should be attributed to the even distribution of nano‐CaCO₃ particles and the formation of γ‐PP and the increase of the degree of cystallinity. Copyright © 2007 Society of Chemical Industry     

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     

The study on the creep of calcium carbonate-filled polypropylene (PP/CaCO<Subscript>3</Subscript>) prepared at different vibration condition

A vibration force field had been introduced during the polymer injection processing in the article, which caused some physical properties of the articles were significantly improved. The creep behavior of calcium carbonate-filled polypropylene (PP/CaCO₃) prepared at different vibration condition was studied in order to reveal the influence of vibration conditions on the creep behavior. First, the tensile creep behavior of the PP/CaCO₃ prepared at different vibration conditions has been investigated with a tensile creep apparatus, and it had been observed that with the vibration frequency increasing, the tensile strain would be maximum value at 0.72 Hz. While the tensile strain of the PP/CaCO₃ prepared at different vibration pressure would be decreasing with the vibration pressure increasing. Then the wide-angle X diffraction (WAXD) and the differential scanning calorimeter (DSC) were used to explore the microstructure of the PP/CaCO₃ article prepared at different vibration condition. According to the WAXD and DSC data, the number of the crystal grain may play an important role on the change of the creep behaviors of PP/CaCO₃ article prepared at different vibration conditions. Finally, the inner reason why the different vibration condition would cause different creep behavior could be found that if the number of the crystal grain is larger, then there would be stronger physical cross-linking structure, which causes stronger anti-creep ability.     

振动注塑PP/CaCO3的拉伸蠕变研究

采用自制的机械振动注塑机,在不同振动频率和振动压力下成型PP/CaCO3试样.考察了试样的拉伸蠕变.结果表明,当振动压力一定时,PP/CaCO3的拉伸应变随着振动频率的增加先增大后减小,当振动频率为15 Hz时达最大;而当振动频率一定时,材料的拉伸应变随着振动压力的增大而减小.通过对不同成型条件下注塑的PP/CaCO3材料进行了短时拉伸实验和动态力学性能测试,从材料柔性和刚性分析其蠕变原因.     

电磁动态注射机振动参数对PP力学性能的影响

采用电磁动态注射机注塑成型PP试样,并对其进行拉伸强度、冲击强度和DSC测试,探讨振动频率和振幅对制品力学性能的影响。结果表明:施加振动后,拉伸强度和冲击强度提高;熔点向高温漂移,有利于结晶完善程度的提高。对PP注塑料,电磁动态注塑成型时最佳的振动参数范围为f=3～9Hz,A=0 10mm～0 40mm。     

Mechanical properties and morphology of polypropylene‐calcium carbonate nanocomposites prepared by dynamic packing injection molding

In this article, dynamic packing injection molding (DPIM) technology was used to prepare injection samples of Polypropylene‐Calcium Carbonate (PP/CaCO₃) nanocomposites. Through DPIM, the mechanical properties of PP/nano‐CaCO₃ samples were improved significantly. Compared with conventional injection molding (CIM), the enhancement of the tensile strength and impact strength of the samples molded by DPIM was 39 and 144%, respectively. In addition, the tensile strength and impact strength of the PP/nano‐CaCO₃ composites molded by DPIM increase by 21 and 514%, respectively compared with those of pure PP through CIM. According to the SEM, WAXD, DSC measurement, it could be found that a much better dispersion of nano‐CaCO₃ in samples was achieved by DPIM. Moreover, γcrystal is found in the shear layer of the DPIM samples. The crystallinity of PP matrix in DPIM sample increases by 22.76% compared with that of conventional sample. The improvement of mechanical properties of PP/nano‐CaCO₃ composites prepared by DPIM attributes to the even distribution of nano‐CaCO₃ particles and the morphology change of PP matrix under the influence of dynamic shear stress. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermomechanical properties of virgin and recycled polypropylene impact copolymer/CaCO3 nanocomposites

The effect of successive injection moldings on the thermal, rheological, and mechanical properties of a polypropylene impact copolymer (PP) was investigated. The crystal content decreased as the molecular weight decreased due to chain scission with repeated injection molding. The Young modulus and the yield stress remained constant, despite a drop in the strain to break. Virgin and recycled PP matrix were filled with nanosized calcium carbonate (CaCO₃) particles. The effect of morphology on the thermal and mechanical properties of nanocomposites of virgin and recycled PP filled with nanosized CaCO₃ particles was also studied. The mechanical properties of the nanocomposites were strongly influenced by the intrinsic toughness of the matrix and the concentration and dispersion of the filler. The yield strength and strain of virgin PP decreased gradually, while its Young's modulus increased slightly with increasing CaCO₃ loading. These phenomena were less pronounced for the recycled matrix. Incorporation of nanoparticles to virgin matrix produced an increase in tensile stiffness and ductility, when good dispersion of the filler was achieved. However, the impact strength dropped dramatically for high filler contents. A significant increase in impact strength was observed for the recycled PP. POLYM. ENG. SCI., 50:1904–1913, 2010. © 2010 Society of Plastics Engineers     

Effect of vibration parameters of electromagnetic dynamic plastics injection molding machine on mechanical properties of polypropylene samples

Dynamic injection processing experiments have been carried out on polypropylene using the self‐made electromagnetic dynamic plastics injection molding machine, and the effects of the vibration force field on mechanical properties of molding samples are studied, namely, the influence of vibration frequency and vibration amplitude on the mechanical properties of samples are researched by using tensile testing, impact testing, differential scanning calorimeter (DSC) and scanning electronic micrograph (SEM) techniques. The results show that the tensile strength and impact strength are both enhanced and the melting point shifts toward the higher temperature, which facilitates the perfection of crystal. The best vibration parameters for processing polypropylene using electromagnetic dynamic plastics injection molding machine are that frequency is from 3 to 9 Hz and amplitude is from 0.1 to 0.4 mm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 972–976, 2006     

塑料动态注射充模过程工艺参数的优化研究

运用了Taguchi方法研究了PP动态注射成型工艺参数对制品性能的影响。研究结果表明，在注射速度、保压压力、振动频率与振幅这四个工艺参数中，在所设定的工艺范围内，对制品性能影响比较明显的是振动频率与振幅。PP试样的冲击强度随振动频率改变而改变，且在10Hz左右存在一个最佳状态，冲击强度可以增加42％。拉伸性能随着振幅的增加基本上呈上升的趋势，极限拉伸应力最大增加8％，弹性模量最大可增加18．7％。在优化的振动工艺参数下，即在1～5Hz的频率段振幅对制品的拉伸性能的影响较之明显，在7～15Hz的频率段振动频率对制品的冲击性能的影响较显著。     

Polystyrene/CaCO3 composites with different CaCO3 radius and different nano‐CaCO3 content—structure and properties

The Archimedes' principle and physical theory are attempted to analysis the densification and structure of the polystyrene (PS) composites by melt compounding with CaCO₃ having different particle size. The difference between the measured specific volume (ν) andthe theoretically calculated specific volume (ν_mix), Δν = ν−ν_mix, can reflect the densification of the composites. It is clearly demonstrated that the PS composites become more condensed with the reduction of the CaCO₃ particle size. Especially, when the content for nano‐CaCO₃ achieves 2 wt%, the Δν value of the composites reaches the least, which shows the best densification. Meanwhile, the glass transition temperature (T_g) reaches the maximum value of about 100°C by differential scanning calorimetry (DSC) and thermal mechanical analysis (TMA), which indirectly reveals the composites microstructure more condensed. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that 2 wt% nano‐CaCO₃ uniformly disperses in PS composites. The CaCO₃ selected in this experiment has certain toughening effect on PS. The impact and tensile strength increase with addition of nano‐CaCO₃, but the elongation at break decreases. When nano‐CaCO₃ content achieved 2 wt%, the impact and tensile strength present the maximum value of 1.63 KJ/m² and 44.5 MPa, which is higher than the pure PS and the composites filled with the same content of micro‐CaCO₃. POLYM. COMPOS., 31:1258–1264, 2010. © 2009 Society of Plastics Engineers     

全程振动注塑对PP力学性能影响的研究

以实际生产条件为前提,在频率0～12Hz、振幅0～0．28mm范围内研究了振动对聚丙烯(PP)力学性能和冲击断面形态结构的影响。结果表明,PP的力学性能对振动参数的响应并不完全是一个单调趋势,而是存在一个最佳的响应范围;全程振动注塑能够同时提高PP的拉伸强度和冲击强度,最大增幅分别为17％和27％。     

Study of rheological behavior of calcium carbonate‐filled polypropylene in dynamic extrusion process

A novel rheological measuring apparatus was designed, which introduced an additional sinusoidal vibration in parallel on the extruding direction of melt polymer in this article. Melt rheology of polypropylene filled uncoated CaCO₃ particles in 3 and 20 %wt amounts of filler during capillary melt‐extrusion was investigated, respectively. A mathematical model of melt polymer under the action of vibration was set up. The effects of vibration parameters on rheological behaviors were studied. The apparent viscosity of filled system decreased remarkably with the increasing vibration frequency and amplitude. The apparent viscosity reached to minimum value when the vibration frequency was 8 Hz. POLYM. COMPOS., 36:630–634, 2015. © 2014 Society of Plastics Engineers     

动态塑化过程振动参数对聚丙烯性能的影响

采用新型液压脉振式注射机成型聚丙烯(PP)试样,探讨了塑化过程中振幅和频率对PP物理力学性能和成型过程整机能耗的影响。结果表明:保持其他工艺参数不变,在塑化过程中施加振动后,PP试样的拉伸强度提高9.8%,冲击强度提高13.8%,密度提高0.3%,整机加工能耗降低6.6%。     

Effects of titanate coupling agents on the rheological and mechanical properties of filled polyolefins

An experimental study was carried out to investigate the effects of titanate coupling agents on the rheological properties of p articulate-filled polyolefin melts. Inorganic fillers used were CaCO₃, talc, and fiberglass, and polyolefins used were high-density polyethylene (HOPE) and polypropylene (PP). It was found that the addition of the coupling agent TTS to the PP-CaCO₃ and PP-fiberglass systems reduced the melt viscosity considerably, whereas the addition of the coupling agent ETDS-201 to the PP-talc and HDPE-talc systems affected the melt viscosity very little. Also carried out was an injection molding study to investigate the effects of different inorganic fillers and the titanate coupling agents used on the mechanical properties of the injection molded specimens. It was found that addition of titanate coupling agents generally resulted in reduced modulus and tensile strength, and increased elongation and impact strength of the filled systems. The PP-CaCO₃-TTS and HDPE-talc-ETDS 201 systems were found to have impact strength improved by approximately 100 percent with the addition of a titanate coupling agent. The PP-CaCO₃-TTS samples have ultimate tensile elongation approaching that of virgin PP.     

Polypropylene/calcium carbonate nanocomposites

Polypropylene (PP) and calcium carbonate nanocomposites were prepared by melt mixing in a Haake mixer. The average primary particle size of the CaCO₃ nanoparticles was measured to be about 44 nm. The dispersion of the CaCO₃ nanoparticles in PP was good for filler content below 9.2 vol%. Differential scanning calorimetry (DSC) results indicated that the CaCO₃ nanoparticles are a very effective nucleating agent for PP. Tensile tests showed that the modulus of the nanocomposites increased by approximately 85%, while the ultimate stress and strain, as well as yield stress and strain were not much affected by the presence of CaCO₃ nanoparticles. The results of the tensile test can be explained by the presence of the two-counter balancing forces—the reinforcing effect of the CaCO₃ nanoparticles and the decrease in spherulite size of the PP. Izod impact tests suggested that the incorporation of CaCO₃ nanoparticles in PP has significantly increased its impact strength by approximately 300%. J-integral tests showed a dramatic 500% increase in the notched fracture toughness. Micrographs of scanning electron microscopy revealed the absence of spherulitic structure for the PP matrix. In addition, DSC results indicated the presence of a small amount of β phase PP after the addition of the calcium carbonate nanoparticles. We believe that the large number of CaCO₃ nanoparticles can act as stress concentration sites, which can promote cavitation at the particle-polymer boundaries during loading. The cavitation can release the plastic constraints and trigger mass plastic deformation of the matrix, leading to much improved fracture toughness.     

Performance evaluation of synthesized acrylic acid grafted polypropylene within CaCO3/polypropylene composites

A polymeric coupling agent acrylic acid grafted polypropylene (AAgPP) was synthesized and its efficiency in CaCO₃/PP composite was investigated. The grafting of acrylic acid monomer (AA) onto polypropylene was performed using an internal mixer. The effect of peroxyde, acrylic acid monomer content, temperature and RPM was studied. A grafting reaction between the polypropylene and the acrylic acid was evidenced through FTIR, UV, DSC and MFI testing. The highest grafting yield was obtained at 0.85 phr peroxide and 5 phr acrylic acid. The selected mixing temperature was 200°C, the rotor speed 150 rpm and the residence time 5 min. The obtained coupling agent (AAgPP) was used with 30 wt% CaCO₃ filled polypropylene. Strong interactions with the composite were observed. The effect of increasing the coupling agent content on Izod impact and tensile properties was investigated. A maximum in the above properties is attained at 15 wt% AAgPP. The most important effect is clearly shown in the Izod test. In fact, a threefold increase has been observed for either notched and untoched specimen. The 15 wt% AAgPP is considered to be a critical concentration for the composite considered. This corresonds to maximum interactions occurring between the matrix and the filler. SEM analysis clearly shows strong interactions between the filler and the matrix in the presence of acrylic acid grafted polypropylene. This is another proof of the efficiency of the synthesized AAgPP as a potential coupling agent for CaCO₃ filled PP.     

Investigation on β‐polypropylene/PP‐g‐MAH/ surface‐treated calcium carbonate composites

β‐Polypropylene composites containing calcium carbonate treated by titanate coupling agent (T‐CaCO₃) and maleic anhydride grafted PP (PP‐g‐MAH) were prepared by melt compounding. The crystallization, morphology and mechanical properties of the composites were investigated by means of differential scanning calorimetry, wide‐angle X‐ray diffraction, polarized light microscopy, scanning electron microscopy and mechanical tests. It is found that both T‐CaCO₃ and NT‐C are able to induce the formation of β‐phase, and NT‐C greatly increases the β content and decreases the spherulitic size of PP. PP‐g‐MAH facilitates the formation of β‐form PP and improves the compatibility between T‐CaCO₃ and PP. Izod notched impact strength of β‐PP/T‐CaCO₃ composite is higher than that of PP/T‐CaCO₃ composite, indicating the synergistic toughening effect of T‐CaCO₃ and β‐PP. Incorporation of PP‐g‐MAH into β‐PP/T‐CaCO₃ composite further increases the content of β‐crystal PP and improves the impact strength and tensile strength when T‐CaCO₃ concentration is below 5 wt%. The nonisothermal crystallization kinetics of β‐PP composites is well described by Jeziorny's and Mo's methods. It is found that NT‐C and T‐CaCO₃ accelerate the crystallization rate of PP but the influence of PP‐g‐MAH on crystallization rate of β‐PP composite is marginal. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Optimization of mechanical properties of PP/Nanoclay/CaCO3 ternary nanocomposite using response surface methodology

Response surface method of experimental design was applied to optimize the mechanical properties of polypropylene (PP)/nanoclay/CaCO₃ hybrid ternary nanocomposite using three different levels of melt flow index (MFI) of PP, nanoclay, and CaCO₃ contents. The samples were prepared by melt mixing in a lab scale corotating twin screw extruder. The main effect of each parameter on the tensile modulus, tensile strength, and impact strength was extensively discussed. The structure of obtained nanocomposite was studied using X‐ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) techniques. Tensile modulus and impact resistance of prepared ternary nanocomposite were correlated to considered parameters using a second‐order polynomial model. Also, the optimum values of studied variables were determined using contour plots. The obtained results show that increasing the nanoclay and CaCO₃ contents improve the tensile modulus up to 45%, whereas the optimum value of impact strength, about 54%, is achieved at low concentrations of nanoclay (2 wt %) and CaCO₃ (8 wt %). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Melt strength of calcium carbonate filled polypropylene melts

This paper investigates the extensional rheology (through melt strength measurement) of calcium carbonate (CaCO₃) filled polypropylene (PP) melts. Different concentrations of CaCO₃ filled PP were produced by mixing two master batches of pure PP and 70 wt% CaCO₃ filled PP in required proportions in a counter‐rotating twin‐screw extruder. It was found that the melt strength of the CaCO₃–PP melts was independent of CaCO₃ concentrations up to 25 vol%. Further increase in CaCO₃ concentration led to a severe reduction of melt strength. © 2002 Society of Chemical Industry     

振动力场对聚丙烯/纳米碳酸钙复合材料性能的影响

采用自行研制的振动注射装置在注射保压过程中对聚合物熔体施加低频振动,成型了聚丙烯/纳米碳酸钙复合材料。对样品进行了力学性能测试并采用SEM对它的冲击断面进行研究。结果表明,采用振动注射成型装置可以使碳酸钙粒子在基体中的分散性得到改善。与常规注射相比,经振动注射后,复合材料的拉伸强度提高了17.6%,冲击强度提高了179.6%。