Mechanical and microstructural properties of Nylon-12/carbon black composites: Selective laser sintering versus melt compounding and injection molding

Composites of Nylon-12 reinforced with 4 wt.% carbon black (CB) manufactured by selective laser sintering (SLS) are compared in terms of flexural strength and flexural modulus, tensile strength and tensile modulus, and impact strength to composites made by extrusion and injection molding (Ex-IM). The Nylon-12 system made by SLS had 25% and 35% higher flexural and tensile modulus, respectively, compared to the Nylon-12 system made by Ex-IM and ∼10% higher strength. However, upon addition of CB both the modulus and the strength of the composites made by SLS were significantly lower compared to composites made by Ex-IM. This is due to the poor dispersion of nanoscale CB and due to the higher porosity of the composites made by SLS, which also explains the relatively low impact strength observed. Based on XRD and DSC studies, it is concluded that the composites made by the two processing methods did not differ significantly in their crystallization characteristics such as the degree of crystallinity, crystal type, and lamellar thickness. However, it was found that CB acted as a nucleating agent for Nylon-12 when Ex-IM was used, leading thus to smaller but more numerous polymer crystals.     

Mechanical properties of textile-inserted PP/PP knitted composites using injection–compression molding

This paper concentrates on the experimental investigation of the self-reinforced all-polypropylene composites. There exists an optimum processing condition to produce high quality specimens by injection–compression molding. Tensile and 3-point bending properties of the virgin PP materials were nearly unaffected by the introduction of reinforcing knit layer(s) due to very low fibre content of the knitted fabrics used. 3-point bending properties were also unaffected by the surface of indentation-flexure. The applied impact energy was maintained at 5 J for the homo-PP and 27 J for the block-PP materials, respectively, to cause penetration during drop-weight impact tests. It is interestingly noteworthy that the self-reinforced homo-PP composites exhibited superior energy absorption capability when compared with the virgin matrix materials. The corresponding plate bending performances of the self-reinforced homo-PP composites also revealed consistent improvement as compared to their virgin counterparts. On the other hand, although virgin block-PP material exhibited better impact performances than its composite reinforced by the homo-PP knitted fabric, a notably small increase in the reinforcement fibre content revealed considerable improvement in the impact properties comparable to those of the virgin block-PP matrix materials. These self-reinforced homo-PP/block-PP materials have clearly indicated that they have the potential to out-perform the block-PP materials via modification and/or manipulation of the reinforcement knit structural/geometrical parameters and the content of reinforcement fibres. Both static and dynamic impact properties are likely to be affected by the local area properties of the tested face under indentation, and thereby contributing to the improved performances of the composite specimens with the knit face under the impact.     

反应注射成型纳米CuS/PDCPD复合材料的制备与性能

以钨配合物为主催化剂, AlEt₂Cl为助催化剂, 表面改性CuS纳米粉体为填料, 采用反应注射成型工艺, 原位聚合方法制备了纳米CuS/聚双环戊二烯(CuS/PDCPD)复合材料。利用红外光谱、 扫描电镜、 透射电镜、 三维轮廓测定仪、 高温气氛摩擦磨损试验机等多种手段对表面改性CuS纳米粉体及纳米CuS/PDCPD复合材料的结构、 填料分散性、 磨损形貌、 力学性能以及摩擦磨损性能进行了表征和测试。结果表明, 改性CuS在极低的添加范围内, 即可实现对PDCPD同时起到增强增韧和耐磨的作用; 在CuS添加质量分数为1% 时, 纳米CuS/PDCPD复合材料的综合性能达到最佳; 与PDCPD性能相比, 冲击强度、 拉伸强度和弯曲强度的最大提高量分别为13.2%、 22.0%、 13.8%; 磨损质量和摩擦因数最大降低了31%和36%。表面改性CuS纳米粉体在PDCPD基体中具有良好的界面相容性,是实现纳米CuS/PDCPD复合材料在低添加范围内具有较佳力学性能和耐磨性能的重要原因。     

反应注射成型纳米CuS/PDCPD复合材料的制备与性能

以钨配合物为主催化剂,AlEt2 Cl为助催化剂,表面改性CuS纳米粉体为填料,采用反应注射成型工艺,原位聚合方法制备了纳米CuS/聚双环戊二烯(CuS/PDCPD)复合材料.利用红外光谱、扫描电镜、透射电镜、三维轮廓测定仪、高温气氛摩擦磨损试验机等多种手段对表面改性CuS纳米粉体及纳米CuS/PDCPD复合材料的结构、填料分散性、磨损形貌、力学性能以及摩擦磨损性能进行了表征和测试.结果表明,改性CuS在极低的添加范围内,即可实现对PDCPD同时起到增强增韧和耐磨的作用;在CuS添加质量分数为1％时,纳米CuS/PDCPD复合材料的综合性能达到最佳;与PDCPD性能相比,冲击强度、拉伸强度和弯曲强度的最大提高量分别为13.2％、22.0％、13.8％;磨损质量和摩擦因数最大降低了31％和36％.表面改性CuS纳米粉体在PDCPD基体中具有良好的界面相容性,是实现纳米CuS/PDCPD复合材料在低添加范围内具有较佳力学性能和耐磨性能的重要原因.     

Investigation on mechanical properties of woven alovera/sisal/kenaf fibres and their hybrid composites

The go-green concept results in multipoint focus towards materials made from nature; easily decomposable and recyclable polymeric materials and their composites along with natural fibres ignited the manufacturing sectors to go for higher altitudes in engineering industries. This is due to the health hazard and environmental problems faced in manufacturing and disposal of synthetic fibres. This study was undertaken to analyse the suitability of new natural fibre as an alternative reinforcement for composite materials. In this paper, tensile, flexural and impact test is made for the woven alovera and kenaf (AK), sisal and kenaf (SK), alovera, sisal and kenaf fibre hybrid epoxy composites (ASK). The composite laminates are made through a hand-layup process. The surface analysis is studied through scanning electron microscopy. From the investigation the SK hybrid composite shows good tensile property, AK hybrid composite shows better flexural property and the best impact strength is observed for ASK hybrid composite. The natural fibres slowly replace the synthetic fibres from its environmental impact, marching towards a revolution in engineering materials.     

PET-MFIAA/ PP原位成纤复合材料的形态结构及力学性能

用钉挂预埋多功能界面活化剂(MFIAA)的PET(PET-MFIAA)与PP共混 - 挤出 - 拉伸,制备了PET-MFIAA/PP原位成纤复合材料,采用扫描电镜、偏光显微镜观察和力学性能测定的方法,研究了PET-MFIAA/PP的PET微纤形态、试样断面形态及力学性能,并与PET/PP、MFIAA/PET/PP两种原位成纤复合材料进行对比。结果表明: PET-MFIAA/PP PET微纤与PP基体间具有强的相互作用,PET微纤呈粗细不均匀、凹凸不平的异形形态及柔性界面等结构特征,形成了强的界面结合,其刚性、韧性均比纯 PP明显提高,含7.00% MFIAA的PET-MFIAA/PP复合材料的拉伸屈服应力、弯曲弹性模量和悬臂梁缺口冲击强度分别达到了纯PP的1.04倍、1.23倍和1.79倍。     

Novel manufacturing process for improving mechanical properties of flax/PP composites

Many attempts have been made in the recent past to improve the mechanical properties of flax/polypropylene (PP) thermoplastic composites. Most of these attempts have not been translated at industrial level due to additional chemical treatment process involved. In the present work, needle-punched nonwoven preforms which can be readily used for composite manufacturing was prepared. To improve the interfacial bonding of the composites, a new modified route for composite preparation is proposed. The modified processing strategy implemented to produce flax with polypropylene composite using compression molding machine. The nonwoven preforms were heated to elevated temperatures followed by quenching. The composite samples were then hot consolidated and their mechanical properties were studied and compared with the samples produced by the conventional method. 154, 75, 37, and 9.6% of improvement have been observed for peel strength, compressive strength, hardness, and impact strength, respectively. The reasons for the improvement are discussed in detail using various analytical tools.     

注塑级聚烯烃塑木复合材料性能研究

制备了注塑级塑木复合材料,研究了木粉添加量对塑木注塑成型复合材料流变性能、弯曲性能和熔融结晶性能的影响。结果表明:随木粉添加量的增加,塑木注塑成型复合材料弯曲强度、弯曲模量和熔融峰温度均出现先增加再降低的现象,当木粉添加量在30份时,复合材料弯曲强度达到30.85MPa,弯曲模量达到3065.21MPa,熔融峰温度也达到最高。     

The mechanical properties of MWNT/PMMA nanocomposites fabricated by modified injection molding

This paper established the procedure to fabricate MWNT/PMMA nanocomposite by using both the injection molding and film casting processes. The combined fabrication process could remove demerits while maintaining the merits of each process. Tensile strength of the MWNT/PMMA nanocomposite increased more than 15% and tensile stiffness also increased about 17.5%, compared to the pure PMMA. It was confirmed that this combined fabrication process efficiently dispersed MWNTs in the PMMA matrix, and also maintained the well-dispersed state more effectively. SEM images of the fractural surface show that the degree of dispersion was improved. In addition, a surfactant was used to disperse MWNTs more efficiently, and its effect on mechanical properties was also investigated.     

Transcrystallisation in PP/flax composites and its effect on interfacial and mechanical properties

The effect of flax fibre reinforcement on the crystallisation behaviour of polypropylene (PP) was investigated using a hot-stage polarising optical microscope. To follow the crystallisation kinetics, crystallisation temperature and time were varied. At crystallisation temperatures between 130 and 138 °C the most uniform and thickest transcrystalline layers were formed. The effect of transcrystallisation on the interfacial shear strength (IFSS) in micro-composites was studied by the fibre pull-out test method. It was found that the IFSS of the PP/flax system is slightly decreased with the presence of a transcrystalline interphase. Finally, the influence of the formation of a transcrystalline zone on the macromechanical properties of compression moulded PP/flax composites was studied.     

The effect of alkaline treatment on mechanical properties of kenaf fibers and their epoxy composites

In this work, kenaf fibers were pre-treated in a NaOH solution (6% in weight) at room temperature for two different periods (48 and 144 h). The chemical treatment of kenaf fibers for 48 h allowed to clean their surface removing each impurity whereas 144 h of immersion time had detrimental effect on the fibers surface and, consequently, on their mechanical properties.Untreated and NaOH treated kenaf fibers (i.e. for 48 h) were also used as reinforcing agent of epoxy resin composites. The effect of the stacking sequence (i.e. using unidirectional long fibers or randomly oriented short fibers) and the chemical treatment on the static mechanical properties was evaluated showing that the composites exhibit higher moduli in comparison to the neat resin. As regards the strength properties, only the composites reinforced with unidirectional layers show higher strength than the neat resin. Moreover, the alkali treatment increased the mechanical properties of the composites, due to the improvement of fiber–matrix compatibility.The dynamic mechanical analysis showed that the storage and the loss moduli are mainly influenced by the alkali treatment above the glass transition temperature. Moreover, the alkali treatment led to a notable reduction of tan δ peaks in addition to significant shifts of tan δ peaks to higher temperatures whereas the stacking sequence did not influence the trends of storage modulus, loss modulus and damping of the composites.     

Effects of extrusion temperature on the rheological,dynamic mechanical and tensile properties of kenaf fiber/HDPE composites

The effects of extrusion processing temperature on the rheological, dynamic mechanical analysis and tensile properties of kenaf fiber/high-density polyethylene (HDPE) composites were investigated for low and high processing temperatures. The rheological data showed that the complex viscosity, storage and loss modulus were higher with high processing temperature. Complex viscosities of pure HDPE and 3.4 wt% composite with zero shear viscosity of ⩽2340 Pa s were shown to exhibit Newtonian behavior while composites of 8.5 and 17.5 wt% with zero shear viscosity ⩾30,970 Pa s displayed non-Newtonian behavior. The Han plots revealed the sensitivity of rheological properties with changes in processing temperature. An increase in storage and loss modulus and a decrease in mechanical loss factor were observed for 17.5 wt% composites at high processing temperature and not observed at low processing temperature. Processing at high temperature was found to improve the tensile modulus of composites but displayed diminished properties when processed at low processing temperature especially at high fiber content. At both low and high processing temperatures, the tensile strength and strain of the composite decreased with increased content of the fiber.     

Effect of interfacial interaction on morphology and mechanical properties of PP/POE/BaSO4 ternary composites

Ternary composites of Polypropylene (PP)/ethylene-octene copolymer (POE)/Barium Sulfate (BaSO₄)(PP/POE/BaSO₄) were prepared through a two-step process: BaSO₄ master-batches were first prepared through blending of BaSO₄ and POE, then blending with PP. Two families of phase structure were confirmed through SEM and DSC, depending on their interfacial interaction. Separation of POE and BaSO₄ filler was found when untreated or titanate coupling agent treated BaSO₄ filler were used. Encapsulation of BaSO₄ particles by POE elastomer was achieved by using BaSO₄ master-batch prepared through reactive blending of BaSO₄ with POE in the presence of maleic anhydride (MAH) and dicumyl peroxide (DCP). The mechanical properties of the composites greatly rely on the morphology. The yield strength and the impact toughness of a composite with core-shell morphology are higher than those of composites with separated morphologies, but the former has lower flexural modulus and elongation at break than the latter. The interfacial interaction was evaluated by semi-empirical equations developed previously. The deformation and toughening mechanisms of the composites were also investigated.     

橡纤混杂型PP/PET/MFC/HET原位成纤复合材料的形态结构和力学性能

采用扫描电镜观察、透射电镜观察、偏光显微镜观察、力学性能测试等方法,研究了橡纤混杂型PP/PET/MFC/HET原位成纤复合材料的微纤结构、断面形态和力学性能.结果表明:多功能增容剂MFC对体系起着反应性增容和橡胶增韧的双重功效,加入"适量"MFC,有利于形成精细化程度更高、承载能力更强的PET微纤;MFC、HET对复合材料断面形态的影响显著,断裂机理由典型的脆性断裂转变为韧性断裂;提高基体PP的熔体流动速率,复合材料力学性能的绝对值和相对于基体提高的幅度都增大,HFPP/PET/MFC/HET的NIIS、TYS和FM分别达到原料HFPP的3.49倍、99%和1.73倍,实现了PET微纤、MFC、HET的协同增强.     

PLA/algae composites: Morphology and mechanical properties

Bio-composites with poly(lactic) acid as matrix and various algae (red, brown and green) as filler were prepared via melt mixing. Algae initial size (below 50 μm and between 200 and 400 μm) and concentration (from 2 to 40 wt%) were varied. First, algae morphology, composition and surface properties are analysed for each algae type. Second, an example of algae particle size decrease during processing is given. Finally, tensile properties of composites are analysed. The surface of algae flakes was covered with inorganic salts affecting filler–matrix interactions. The Young’s modulus of composites increased at 40 wt% load of algae as compared with neat PLA although the strain at break and tensile strength decreased. In most cases the influence of algae type was minor. Larger flakes led to better mechanical properties compared to the smaller ones.     

机械合金化后注射成形制备Cu/Al2O3复合材料的显微组织与力学性能

采用机械合金化后注射成形制备10%(体积分数,下同)Cu/Al_2O_3复合材料,研究机械合金化时间、烧结温度对复合材料显微组织和性能的影响,并分析复合材料的增韧机理。结果表明:通过机械合金化10h后注射成形、脱脂、1550℃烧结工艺制备的10%Cu/Al_2O_3复合材料具有良好的抗弯强度和断裂韧度,分别为532MPa和4.97MPa·m^1/2;烧结温度低于1550℃导致原子在固态下扩散能力不足,烧结温度高于1550℃则使颗粒边界移动速率大于孔隙逸出速率,二者都造成复合材料孔隙率增加,而导致材料的强度和韧度下降;机械合金化时间延长使复合材料晶粒细化、Cu与Al_2O_3之间的结合强度提高,材料强度和硬度提高,但断裂韧度下降;Cu粉末弥散分布于Al_2O_3基体中,抑制烧结过程中Al_2O_3晶粒粗化,且使裂纹在扩展过程中遇到延性的Cu产生裂纹桥联和偏转,提高材料的韧度。     

Influence of feeding conditions in twin-screw extrusion of PP/MWCNT composites on electrical and mechanical properties

The influence of feeding conditions of multiwalled carbon nanotube (MWCNT) materials, namely Baytubes® C150P and Nanocyl™ NC7000, into polypropylene (PP) was investigated with respect to achieving suitable nanotube dispersion, high electrical conductivity, and good mechanical properties. Both MWCNT materials were fed at selected concentrations either in the hopper of the twin-screw extruder or using a side feeder under otherwise identical extrusion conditions (rotation speed, throughput, temperature profile) using a Berstorff ZE 25 twin-screw extruder. Afterwards, injection molding was performed under identical conditions. The results indicate that the more compact Baytubes® C150P agglomerates should be added into the hopper, as the dispersion assessed by light microscopy is better, electrical resistivities measured on compression and injection molded samples are lower, and elastic modulus, yield strength and impact strength are higher as compared to side feeding. On the other hand, for the more loosely packed Nanocyl™ NC7000 agglomerates, addition using the side feeder leads to better dispersion, lower electrical resistivity, and higher mechanical properties.     

The effect of molecular weight on the interfacial properties of GF/PP injection molded composites

It is well established that the molecular weight of recycled PP decreases significantly as compared to the virgin material. Hence this study involved 2 PP grades of different molecular weights in order to simulate the recycling process. The effect of weight–average molecular weight on interfacial adhesion between GF and PP was investigated. Tensile test was done and the fiber length distribution around the fracture zone in both composites was compared with the distributions from similar locations of unstressed composites. The effect of PP-grafted maleic anhydride coupling agent was also studied. It was found that a decrease in weight–average molecular weight of PP improved interfacial adhesive strength between GF/PP. The lower molecular weight matrix has a lower viscosity that enables its molecules to penetrate easily into the silane interphase. In that case, the interfacial area that is available for coupling is higher, leading to a more effective coupling. The higher interfacial shear strength between the glass fiber and the lower molecular weight matrix induced more breakage of the glass fiber during tensile test.     

Damage of the cell wall during extrusion and injection molding of wood plastic composites

To study material damage in wood cells during any transformation process, one must consider the molecular architecture of natural cellulosic fibers, which may eventually impact the overall mechanical behavior of wood fibers. In particular wood species, anatomical features and mechanical properties of the cell wall may determine the potential for stress transfer in hybrid materials. In this study, we quantified wood cell damage in terms of the stiffness reduction of the S2 layer for the cell wall by measuring Young’s modulus with nanoindentations of the cell wall before and after processing. We then propose and validate a modified rule of mixtures based on a damage parameter affected by the latewood proportion and cell wall properties.     

Effect of removing polypropylene fibre surface finishes on mechanical performance of kenaf/polypropylene composites

Natural fibre/polypropylene thermoplastic composites are often produced by compression moulding of a blended preform of polypropylene fibre and natural fibre treated by chemicals or enzymes. Two preform processing routes may be adopted: (1) treating the natural fibre first and then blending it with the polypropylene fibre (the pre-treatment route), and (2) forming a blended preform of the natural fibre and polypropylene fibre first and then carrying out the chemical/enzyme treatment on the blended preform (the post-treatment route). The kenaf/polypropylene composites produced according to the post-treatment route show up to 36% higher flexural strength and up to 63% higher flexural modulus than the composites produced according to the corresponding pre-treatment route. These differences were attributed to the chemical surface finishes of the polypropylene fibre, which have been removed in the post-treatment processing route, but persisted into the final composites in the pre-treatment processing route.