Talc as nucleating agent of polypropylene: morphology induced by lamellar particles addition and interface mineral-matrix modelization

The efficiency of talc used as nucleating agent (0.5% by weight) in polypropylene (PP) was determined taking into account the particle size d ₅₀, particle morphology and BET specific surface areas. These findings were compared to a mineral with similar properties, pyrophyllite. Talc samples with the finest particle sizes induce a significant increase in the starting crystallization temperature of PP and irrespective of the particle size d ₅₀, pyrophyllite was found to be less efficient than talc. X-Ray results show that PP oriented crystallization due to talc or pyrophyllite addition, corresponds to an epitaxial growth whereby the mineral c*-axis is merged with the PP b*-axis. Microscopic observations revealed that in the presence of talc, nuclei density of PP increased strongly. In addition, a large number of nuclei was observed to appear everywhere on the talc surface. A PP-talc interface model is proposed by matching the (001) talc plane and the (010) PP plane. In this model, 3% of PP cell accommodation on talc is necessary with a 15° angle between PP chains elongation and the crystallographic directions of talc. Hexagonal rings on talc surface are believed to represent hydrogen bonds with PP methyl groupings. This fine structure relation between talc and PP is discussed, and is used to characterize the differences observed between the efficiency of talc and that of pyrophyllite.     

滑石粉/聚丙烯复合材料结晶度与相间形态对其力学性能的影响

用偶联剂改性的滑石粉（Talc）与聚丙烯（PP）共混制备Talc／PP复合材料,测试了复合材料的力学性能。用广角X射线衍射仪对聚丙烯的结晶状况进行了表征,计算了复合材料中聚丙烯的结晶度;用扫描电镜观察了样条的断口形貌,讨论了滑石粉填充量对材料结晶性能与相态结构的影响．以及PP相结晶度和体系的微相结构对复合材料的拉伸、弯曲及冲击性能的影响。实验结果表明,滑石粉的加入对复合材料的结晶行为、相态结构和力学性能有影响。在15％的滑石粉填充量时,聚丙烯相的结晶度达到最大值,材料的拉伸强度、弯曲强度也基本上达到最大值,而冲击强度却降到最低。扫描电镜照片显示,PP基体的结晶形态与复合材料的相态结构随滑石粉含量的改变而变化。     

应力水平和纤维角度对CGF/PP复合材料蠕变行为的影响及其Burgers模型参数的数值预测

采用DMA的Creep模式分别测试了短时间内（15 min）聚丙烯（PP）在不同应力水平和温度下的单向拉伸蠕变行为,长时间内（10 h）连续玻璃纤维增强聚丙烯（CGF/PP）复合材料单层板在不同应力水平和不同纤维角度上的拉伸蠕变行为。利用Burgers黏弹性模型拟合了蠕变测试数据,构建了相关参数与应力水平和纤维角度的依赖性。结果表明:PP和CGF/PP单层板的蠕变柔量均随应力增大而显著增加,稳态蠕变速率也随之增加,蠕变模量保留率明显下降,PP基体的黏弹性主要决定了CGF/PP单层板在低应力水平下的蠕变行为; 30%应力水平下,偏轴拉伸的纤维角度在0°~90°范围内存在拉-剪耦合效应,在45°时最为显著,此时稳态蠕变速率和蠕变变形量最大;利用四元件Burgers黏弹性模型拟合各条件下蠕变曲线得到的数值模型与实验数据具有较好的相关性,相关系数达到0.99,从得到的数值模型可知相关模型参数存在明显的应力和角度依赖关系;利用模型参数的数值拟合公式分别预测10 MPa应力下0°纤维方向的蠕变曲线及45°纤维方向上30%应力水平的偏轴蠕变曲线均与实验曲线一致,表明本文得到的数值模型的可靠性。      

Application of different macrokinetic models to the isothermal crystallization of PP/talc blends

The crystallization kinetics of neat polypropylene (PP) and of PP composites containing 2, 5, 10 and 30 wt% of talc was studied. Various kinetic equations, namely the Avrami, Velisaris–Seferis, Dietz, Khanna, Malkin models, have been applied to describe the kinetics of crystallization from the melt state under isothermal conditions. The results suggested that experimental data of the Avrami’s exponent, “n”, is approximately 2, meaning that the crystallization of PP alone and of its composites with talc is a two-dimensional growth process. Experimental data of PP alone can be best described by the Avrami, Velisaris–Seferis, Dietz and Malkin models; whereas the models that in the case of composites better correlate their behavior are those of Velisaris–Seferis, followed by Avrami’s.     

Physical and mechanical properties of injection-molded wood powder thermoplastic composites

In the last decades, filler-reinforced thermoplastics especially natural filler-reinforced plastics have been frequently used to improve the physical and thermal properties of polymer materials in plastic industry due to their low density, fully degradable, helpful to reduce the CO₂ emission, free from health hazard and low cost. At current study, wood powder/polypropylene composites (wood/PP) with different filler contents were molded by injection molding process to investigate the effect of filler content on the physical and mechanical properties of the composites. Additionally, the comparison of physical and mechanical properties between talc/PP (which has been widely used in the automotive products) and wood/PP has been carried out based on the tensile, bending, Izod impact tests and the scanning electron microscope observation on the fracture surfaces. Results showed that the highest mechanical property of wood/PP was determined at 30?wt.% wood content. More interesting is that, at the same composite density up to 30?wt.%, the mechanical property of wood/PP was much higher than that of talc/PP. Theoretically, Nielsen equation is often used to predict the elastic modulus of filler reinforced plastics, and in this study, the predicted values were in good agreement with experimental values up to 30?wt.%, after that, they were higher to the experimental values of wood/PP composite. It is considered that is due to the discounted of the distribution and orientation of the filler in the matrix in Nielsen equation.     

PP/Talc复合材料的非等温结晶动力学

用差示扫描量热法(DSC)研究聚丙烯(PP)及PP／Talc复合材料的非等温结晶过程,加入滑石粉后,PP／Talc的结晶速率、结晶度得到明显提高。结合Avrami和Ozawa方程得出一个适合于非等温的结晶动力学方程,并由此获得PP／Talc复合材料的非等温结晶动力学参数,计算表明Talc能促进PP材料的结晶。     

PP/POE/滑石粉三元复合材料的研究

研究了弹性体(POE)、滑石粉、偶联剂和填料处理方式对聚丙烯(PP)的力学性能、加工性能、结晶行为以及无机粒子在基体中分散形态的影响。结果表明,PP 2(K 7726)/POE(80/20)二元共混体系的综合性能较好;采用方式C(将两种偶联剂按1∶1的质量比,先加钛酸酯后加硅烷处理滑石粉)制得的PP 2/POE/T a lc(80/20/25)三元复合材料的力学性能比其它两种方式有显著提高。偏光显微镜(PLM)研究表明,方式C处理的滑石粉在体系中分散性最好;扫描电镜(SEM)显示,三元复合体系由PP 2/POE耗能少的空洞化断裂方式向耗能多的剪切屈服方式转变;DSC表明,采用方式C处理的滑石粉对聚丙烯的成核作用减弱。     

Effect of high filling ratio on the weld strength of hot plate welded calcite filled polypropylene and its comparison with talc filling

In this paper, the effect of the hot plate welding parameters on the weld strength of 40 % calcite filled polypropylene were investigated by utilizing design of experiment and compared to talc filled polypropylene. The plate temperature and the heating time were considered as the process parameters. A mathematical predictive model of the weld strength was developed in terms of welding parameters. The results show that the mathematical model correlates well with the experimental results. The optimum welding parameters of calcite filled polypropylene are determined as 260 °C of plate temperature and heating time of 25 s. The welding strength of the joint welded at optimum parameters is found as 18.32 MPa. Hot plate welding efficiency of the 40 % calcite filled polypropylene is observed to be higher than 40 % talc filled polypropylene material.     

聚丙烯/尼龙1010的失效强度预报

在定义了聚丙烯最小体积分数基础上由聚丙烯(PP)和尼龙1010(PA1010)性能预报了共混物的极限失效强度。试验结果表明,V(PP)／V(PA1010)=40／60时材料强度最低,利用简化力学模型计算的PP最小体积分数约为32％,接近于由共混物微观形貌观察到的发生相转接区域体积分数值,说明材料在相反转区力学性能也有相应的转变。在PP／PA1010中添加增容剂PP—g—MAH使转折点位置发生了变化,失效强度较未加增容剂有所提高．在PA1010含量＞40％时与预报结果符合更好。     

Damage evolution and energy absorption of E-glass/polypropylene laminates subjected to ballistic impact

High-velocity transverse impact of laminated fiber reinforced composites is of interest in military, marine and structural applications. The overall objective of this work was to investigate the behavior of laminated thermoplastic composites of varying thicknesses under high-velocity impact from an experimental and modeling viewpoint. In order to analyze this problem, a series of ballistic impact tests have been performed on plain weave E-glass/polypropylene (E-glass/PP) composites of different thicknesses using 0.30 and 0.50 caliber right-cylinder shaped projectiles. A gas gun with a sabot stripper mechanism was employed to impact the panels. In order to analyze the perforation mechanisms, ballistic limit and damage evaluation, an explicit three-dimensional finite element code LS-DYNA was used. Material model 162, a progressive failure model based on modified Hashin’s criteria, has been assigned to analyze failure of the laminate. The projectile was modeled using Material model 3 (MAT_PLASTIC_KINEMATIC). The laminates and the projectile were meshed using brick elements with single integration points. The impact velocity ranged from 187 to 332 m s⁻¹. Good agreement between the numerical and experimental results was attained in terms of predicting ballistic limit, delamination and energy absorption of E-glass/PP laminate.     

聚丙烯/滑石粉平板状梯度材料的研究--(Ⅰ)制备及表征

将传统的聚合物挤出及复合层压工艺有机地结合起来．采用一种简便易行的加工方法制备了平板状聚丙烯／滑石粉梯度材料．并用TGA、SEM和光学显微镜等分析手段对材料内部的组成和组分分布进行了表征。结果表明．所制材料的组成和组分分布在设定方向上均实现了梯度化．表明本论文所提出的方法是一种制备有机／无机复合梯度材料的有效方法。     

A combined experimental and numerical approach to study ballistic impact response of S2-glass fiber/toughened epoxy composite beams

A combined experimental and 3D dynamic nonlinear finite element (FE) approach was adopted to study damage in composite beams subject to ballistic impact using a high-speed gas gun. The time-histories of dynamic strains induced during impact were recorded using strain gages mounted on the front of the composite beam specimen. During ballistic impact tests, the impact velocity was also measured. The commercially available 3D dynamic nonlinear FE code, LS-DYNA, modified with a proposed user-defined nonlinear-orthotropic damage model, was then used to simulate the experimental results. In addition, LS-DYNA with the Chang–Chang linear-orthotropic damage model was also used for comparison. Good agreement between experimental and FE results was found from the comparisons of dynamic strain and damage patterns. Once the proposed nonlinear-orthotropic damage model was verified by experimental results, further FE simulations were conducted to predict the ballistic limit velocity (V₅₀) using either the number of damaged layer approach or a numerically established relation between the projectile impact velocity versus residual velocity or energy similar to the classical Lambert–Jonas equation for metals.     

非均质秸秆纤维复合材料保险杠蒙皮刚度分析

目的 研究非均质秸秆纤维复合材料保险杠蒙皮的刚度性能.方法 采用试验与模拟分析的方法,通过共混挤出与化学发泡注塑工艺制备微发泡秸秆纤维/聚丙烯(SF/PP)复合材料试样,通过试验测试非均质结构试样的力学性能与微观结构,通过有限元分析手段建立非均质微发泡秸秆纤维/PP复合材料结构分析模型,并分析非均质材料保险杠蒙皮的刚度...     

Tensile modulus of carbon nanotube/polypropylene composites – A computational study based on experimental characterization

Micromechanical and computational models significantly over-predict the tensile modulus of composites, as they ignore many experimentally observed factors. Computational models that capture the effect of polymer-filler contact, the presence of carbon nanotube (CNT) agglomerates and the alignment of CNTs with respect to the applied load on the tensile modulus of CNT-reinforced polypropylene (PP) are proposed and discussed in detail in this study. The CNT/PP composites are made by melt mixing and injection molding. The CNT/PP contact area is characterized in terms of width and modulus using Atomic Force Microscope (AFM). The presence, including the size and distribution of CNT agglomerates, is characterized using Scanning Electron Microscope (SEM). The tensile modulus of CNT/PP composites, measured as a function of CNT content according to ASTM D638, is compared to predictions made using numerical methods based on Finite Element Analysis (FEA) within the composite’s elastic regime. The model over-predicts the modulus of the CNT/PP composites by 85% for 5 wt.% CNT/PP composites assuming perfect filler–polymer interfacial contact. When imperfect CNT/PP contact, CNT agglomerates and alignment are accounted for in the model the effective composite modulus predicted is in good agreement with the experimental data. The computational design tools proposed in this study by systematically incorporating experimentally observed characteristics, in combination with the manufacturing method used to make the CNT/PP composites, can lead to composites with engineered properties made by a scalable and cost effective method.     

Investigation on chloride penetration into unsaturated concrete under short-term sustained tensile loading

Knowledge of the transport properties of chloride in unsaturated concrete subjected to sustained tensile loading is essential for evaluating the durability and predicting the service life of reinforced concrete structures. The objective of this study is to fill this gap by correlating the change in water/chloride diffusivity and penetration profiles with an increasing tensile stress level on unsaturated concrete. A theoretical framework for predicting the one-dimensional movement of chloride into unsaturated concrete under tensile stress state, which is closely associated with capillary absorption of water, is presented. An improved test apparatus aimed for the coupled effect of sustained loading and chloride penetration was designed to real-timely measure the amount of water solution absorbed by the cylindrical hollow concrete specimen. A series of chloride transport experiments were conducted on the saturated, half-saturated and fully dried concrete (i.e. ST, HST and DT) respectively subjected to several tensile stress levels (i.e. 10, 20, 30, 40 and 50% of peak tensile strength). Quantitative data on the profiles of chloride penetration into concrete were acquired to validate the proposed theoretical model. The experimental results indicated that the water/chloride diffusivity and the chloride content increase with the increase of tensile stress level in the range of 0–50%. The quantitative relationship between the water/chloride diffusivity and tensile stress level was obtained. On the basis of above analysis, the numerical results of chloride profiles obtained by the proposed model were in good agreement with those of experimental measurement under various tensile stress levels.     

Dispersion,thermal and mechanical properties of polypropylene/magnesium hydroxide nanocomposites compatibilized by SEBS-g-MA

Isotactic polypropylene (PP)/nano-magnesium hydroxide (nano-MH) composites with 10 wt.% maleic anhydride grafted styrene–ethylene-butylene–styrene tri-block copolymer (SEBS-g-MA) as a compatilizer were prepared by melt extrusion compounding and injection molding. The effects of SEBS-g-MA on dispersion of nano-MHs in PP matrix and interfacial adhesion were studied in order to prepare highly filled PP/MH nanocomposites. The results showed that SEBS-g-MA improved both dispersion of nano-MHs and interfacial adhesion in PP/MH nanocomposites with up to 40 wt.% nano-MHs. The elastic moduli of PP/SEBS-g-MA /MH nanocomposites increased marginally and tensile yield strengths were almost invariant with nano-MH loading. Significant impact toughening of these ternary nanocomposites was, however, achieved due to the cavitation of SEBS-g-MA/MH particles and expansion of voids as well as plastic deformation of the PP matrix.     

相对冲击位置和补片层数对胶接修理CFRP复合材料层合板抗冲击性能的影响

本文针对碳纤维增强聚合物（CFRP）复合材料修补结构,基于连续损伤力学和粘结单元模型,在ABAQUS软件中对低速冲击载荷下不同冲击位置和补片层数的CFRP复合材料层合板内部和层间损伤进行了数值分析,并与试验结果进行了对比。选择相对冲击位置为0 mm、10 mm、20 mm、30 mm和40 mm时对应的五种修补结构,通过数值计算和试验,获得了修补结构在低速冲击过程中的冲击力、冲击能量等数据。在保持补片单层厚度不变的前提下,使补片层数从1层增加到5层,计算获得了修补结构的低速冲击响应。研究结果表明:冲头接触修补结构时会对补片造成较大的损伤,补片可以提高含孔损伤母板的抗冲击性能;冲击点离修补结构损伤孔越近,结构受冲击所产生的分层损伤越严重;增加补片的层数可以提高修补结构的抗冲击性能;通过对补片层数进行优化,得到优化层数为2,其对应的修补结构与无修补结构相比分层损伤面积减少了19.9%,较好地提升了母板的抗冲击性能。      

Effects of filler treatments on the mechanical and morphological behavior of PP+wood flour and PP+sisal fiber

Composites were prepared from waste wood flour, sisal fiber and polypropylene (PP). The surface of the filler was modified to enhance the chemical affinity between hydrophilic cellulosic and hydrophobic polymer. The treatments studied were: a) The addition of a coupling agent; b) chemical treatment with NaOH; and c) the addition of functionalized polypropylene (Polybond 3150 and 3200). After treatment, mixtures of PP with 40% and 20% of the filler, wood flour and sisal fiber respectively, were extruded and injection molded. In the case of wood flour, a mixture of two particle sizes (mesh 20 and 40, 50% each) was used, and in the case of sisal, 10 mm long fibers were selected. Results showed that, regardless of the treatment to which the filler was previously submitted, Young’s modulus was always higher for mixtures prepared with wood flour, with values varying between 2839 and 3150 MPa. Whereas for mixtures with sisal fiber, the modulus’ values varied between 1704 and 2220 MPa. Values of breaking strength, elongation at break and impact strength for PP mixtures with treated sisal fiber were always higher than those for mixtures of PP with wood flour. Based on these results, we can conclude that sisal fiber is an organic filler which, due to its mechanical and morphological characteristics, has a reinforcing effect higher than that of wood flour. Received: 9 October 2000 / Reviewed and accepted: 10 October 2000     

Eggshell, a new bio-filler for polypropylene composites

Chicken eggshell (ES) is an industrial byproduct containing 95% calcium carbonate, and its disposal constitutes a serious environmental hazard. Different proportions of chicken eggshell as bio-filler for polypropylene (PP) composite were compared with different particle sizes and proportions of commercial talc and calcium carbonate fillers by tensile test. The Young's modulus (E) was improved with the increment of ES content, and this bio-filler was better than all types of carbonate fillers with different particle sizes used in this study. Although ES composites showed lower E values than talc composites, talc filler could be replaced by up to 75% with ES while maintaining a similar stiffness and E compared to the talc composites. Scanning electron microscopy showed an improved interfacial bonding on the tensile fractured surface. The improvement in the mechanical properties was attributed to a better ES/matrix interface related to the geometric ratio of the ES particles similar to talc particles.     

Experimental and Numerical Investigation on the Size of Damage Process Zone of a Concrete Specimen under Mixed-Mode Loading Conditions

The characteristic length of a gradient-dependent damage model is a key parameter, which is usually regarded as the length of damage process zone (DPZ). Value and evolution of the size of DPZ were investigated by both a numerical method and an experimental manner. In the numerical study, the geometrical model adopted was a set of four-point shearing beams; the numerical tool used was the Abaqus/Explicit software. The distance between the front and end of a complete DPZ was obtained. Values of strain components at these points were given out at given time points. The experimental study of the evolution process of a damage process zone was investigated with a set of concrete specimens under mixed-mode loading conditions by using a white-light speckle method. The geometrical parameters of the damage process zone were measured. Double-notched specimens under four-point shear loading conditions were adopted. A series of displacement fields for points on the surface of the specimen were measured and further transferred into a strain field of these points during loading process. With reference to the strain values that occurred at both the front and end of a numerically-obtained DPZ, the length of the DPZ was determined with the experimental results. These results provide an experimental basis for the determination of the value of an internal length parameter for a gradient-enhanced and/or area-averaged non-local model.