Comparative impact behaviours of ultra high performance concrete columns reinforced with polypropylene vs steel fibres

Polypropylene(PP) fibres have primarily used to control shrinkage cracks or mitigate explosive spalling in concrete structures exposed to fire or subjected to impact/blast loads, with limited investigations on capacity improvement. This study unveils the possibility of using PP micro-fibres to improve the impact behaviour of fibre-reinforced ultra-high-performance concrete(FRUHPC) columns. Results show that the addition of fibres significantly improves the impact behaviour of FRUHPC columns by shifting the failure mechanism from brittle shear to favourable flexural failure. The addition of steel or PP fibres affected the impact responses differently. Steel fibres considerably increased the peak impact force(up to 18%) while PP micro-fibres slightly increased the peak(3%-4%). FRUHPC significantly reduced the maximum midheight displacement by up to 30%(under 20°impact) and substantially improved the displacement recovery by up to 100%(under 20° impact). FRUHPC with steel fibres significantly improved the energy absorption while those with PP micro-fibres reduced the energy absorption, which is different from the effect of PP-macro fibre reported in the literature. The optimal fibre content for micro-PP fibres is 1% due to its minimal fibre usage and low peak and residual displacement. This study highlights the potential of FRUHPC as a promising material for impact-resistant structures by creating a more favourable flexural failure mechanism, enhancing ductility and toughness under impact loading, and advancing the understanding of the role of fibres in structural performance.

Influence ofβ-nucleating Compound Agents on the Mechanical Properties and Crystallization Behavior of Polypropylene Random Copolymer

A novel polypropylene random(PPR)composite materials with optimized properties was developed by addingβ-nucleating compound agents(rare earth complex WBG-2 and aryl amide derivative TMB-5)and ternary compound modifier(TPE/WBG-2/CaCO_(3)).The effects of differentβ-nucleating agents and ternary compound modifier on the mechanical properties and crystallization behavior of PPR were analyzed.The results show that,compared with pure PPR materials,both WBG-2 and TMB-5 could significantly improve the impact strength of PPR.The crystallization temperature of PPR increased with the addition ofβ-nucleating agent.The modified PPR prepared with ternary compound modifier showed the most excellent comprehensive properties.

CHARACTERISTICS OF STRUCTURE OF IMPACT COPOLYMERS OF POLYPROPYLENE WITH LOW ETHYLENE CONTENTS

In the present work, the structure and impact properties of copolymers of polypropylenewith low ethylene contents have been investigated. Based on the results of ^(13)C--NMR, FTIR,WAXD, DSC, PLM and SEM, the relationship between impact properties and morphology of thecopolymers has been discussed. The high impact properties of copolymer ICP2 may attribute tothe relatively higher ethylene content and homogeneous ethylene unit distribution. The size andits distribution of spherulite in the copolymers and cycloid cavities dispersed in polypropylenecontinue phase may also be two important factors which affect the impact properties of these materials.

Determination and Temperature Dependence of Plateau Modulus for Polymerization of Propylene to Isotactic Polypropylene with Ultra-high Molecular Weight under Catalysis of Ziegler-Natta Catalyst

The viscoelastic behavior of isotactic polypropylene with ultra-high molecular weight(UHPPH) and broad molecular weight distribution(MWD), produced in the presence of Ziegler-Natta catalyst, was investigated by means of oscillatory rheometry at 180 and 200 ℃, whose loss modulus(G″) plots at 180 and 200 ℃ versus the natural logarithm of angular frequency(ω) present a pronounced maximum at 34.35 and 69.21 rad/s, respectively, and do not show a maximum peak at 0.01-100 rad/s for Ziegler-Natta catalyzing ethylene-propylene random copolymerization(PPR) with a conventional molecular weight and broad MWD. The fact indicates that the high molecular weight is responsible for a maximum peak of G″(ω) vs. lnω curves for UHPPH. This makes it possible to determine the plateau modulus(G 0_N) of UHPPH from a certain experimental temperature G″(ω) curve directly. For UHPPH, the G 0_N determined to be 4.28×10 5 and 3.62×10 5 Pa at 180 and 200 ℃, respectively, decreases with the increase of temperature and is independent of the molecular weight, which directly confirms reputation theoretical prediction that the G 0_N has no relation to the molecular weight.

Preparation of Ultra-High Molecular Weight Polypropylene Using Ziegler-Natta Catalyst via Combining Internal Electron Donor and Cocatalyst Loading

Due to the development of the new energy industry,polypropylene with ultra-high molecular weight plays a crucial role for battery isolation membrane.This work investigated the effect of internal electron donor of Ziegler-Natta catalyst system on the molecular weight of the obtained polypropylene.The scanning electron microscope(SEM)and Canon camera were used to characterize the surface morphologies of catalyst particles and polymer particles,respectively.Compared with the polypropylene particles featuring a spherical shape,these study results confirmed that the morphology duplication theory from the catalyst particle to the morphology of polymer particle was exhibited.The gel permeation chromatography(GPC)results revealed that the obtained polypropylene has a much higher average molecular weight than those prepared by conventional method.The Fourier transform infrared spectrometry(FT-IR)and X-ray photoelectron spectroscopy(XPS)revealed that the carbonyl oxygen atom on ester group was preferentially bound to Mg and Ti,as compared to the ether oxygen atom.The XPS results showed that the ratio of Ti^(3+)/Ti^(4+)could be changed by internal electron donors.When Ti3+content was nearly 99%in the Ziegler-Natta catalyst system,isotactic polypropylene with an ultra-high molecular weight of up to 1.42×10^(6)g/mol was obtained by Cat.3.This result implied that internal electron donor ID3 could reduce theβ-hydride elimination reaction to further increase the molecular weight of the obtained polymer.

Effect of maleic anhydride grafted styrene-ethylene-butylene-styrene （MA-SEBS） on impact fracture behavior of polypropylene / wood fiber composites

MA-SEBS as compatibilizer and impact modifier was incorporated into Polypropylene/Wood Fiber （PP/WF） to enhance interface adhesion and impact strength of the composite. The effect of MA-SEBS content on the impact fracture behavior of PP/WF composites was studied. The impact properties of composites with 8% MA-SEBS reached the maximum value. And further increasing of MA-SEBS content to 10% did not improve the fracture toughness, but improved the stiffness of composites by DMA analysis. This was attributed to the improved PP/WF adhesion. As the MA-SEBS content is more than 8%, the molecule interaction of PP and WF was expected to much stronger than lower MA-SEBS. Scanning electron microscopy （SEM） was performed to analyze the impact fracture surface and showed a stronger affinity for the wood surfaces.

Temperature Effect on the Conformation Transition of Ultra-high Molecular Weight Polyethylene/Polypropylene Blends Undergoing Continuous Volume Extensional Flow:A Mesoscopic Simulation

Due to the multiformity and complexity of chain conformation under external flow and the challenge of systematically investigating the transient conformation and dynamic evolution process of polymer chains at the molecular level by means of present experimental techniques,a universal description of both chain conformation and dynamics with respect to continuous volume extensional flow(CVEF)is still absent.Taking into account the temperature effect,we performed dissipative particle dynamics(DPD)simulations with the particles corresponding to the repeat units of polymers over a wide temperature range and analyzed the correlation with the conformational properties of ultra-high molecular weight polyethylene/polypropylene(UHMWPE/PP)blend in response to the CVEF.With time evolution,the polymer chains become highly oriented parallel to the flow direction instead of the initial random coiling and self-aggregation.It is found that a high temperature is necessary for more substantial compactness to take place than low temperature.The low-k plateau and low-k peak in structure factor S(k)curves suggest a low degree of conformational diversity and a high degree of chain stretching.It is also concluded that the intra-molecular C-C bond interaction is the main driving force for the dynamics process of the chain conformations undergoing CVEF,where the motion of the alkyl chains is seriously restricted owing to the increase in bond interaction potential,resulting in a reduction of the difference in diffusion rates among alkyl chains.

Critical Role of Ethylene-Propylene Block Copolymer in Impact Polypropylene Copolymer

Ethylene-propylene block copolymer(EbP) is a vital component in impact polypropylene copolymer(IPC), yet its distribution in the multiphase composite material and how it influences the phase structure and the mechanical properties are not well understood. In this work,four IPCs were investigated by atomic force microscopy-infrared(AFM-IR) to assess the phase compositions in situ, based on which in conjunction with the chain microstructure information obtained ex situ the distributions of the copolymer components were derived for each alloy. For the IPCs whose EbP comprises long P and long E segments, the EbP fraction was found to phase separate from the rubber and the PP matrix to form the cores of the disperse particles with the E-P segmented copolymer(EsP). In contrast, in the IPC with EbP composed of long P and short E segments, the EbP fraction formed an outer shell for the rubber particles with the cores comprising the EsP alone, and this IPC, containing a lower E comonomer content than its counterpart, exhibited both better impact resistance and higher flexural modulus. These results clarify how the chain structure of EbP governs the phase morphology in IPC, which in turn impacts the properties of the composite material.

Reinforcing effects of modified Kevlar~ fiber on the mechanical properties of wood-flour/polypropylene composites

Kevlar fiber （KF） is a synthesized product with strong mechanical properties. We used KF as a reinforcement to improve the mechanical properties of wood-flour/polypropylene （WF/PP） composites. KF was pretreated with NaOH to improve its compatibility with the thermoplastic matrix. Maleated polypropylene （MAPP） was used as a coupling agent to improve the interfacial adhesion between KF, WF, and PP. Incorporation of KF improved the mechanical properties of WF/PP composites. Treatment of KF with NaOH resulted in further improvement in mechanical strength. Addition of 3% MAPP and 2% hydrolyzed KF （HKF） led to an increment of 93.8% in unnotched impact strength, 17.7% in notched impact strength, 86.8% in flexure strength, 50.8% in flexure modulus, and 94.1% in tensile strength compared to traditional WF/PP composites. Scanning electron microscopy of the cryo-fractured section of WF/PP showed that the HKF surface was rougher than the virgin KF, and the KF was randomly distributed in the composites, which might cause a mechanical interlocking between KF and polypropylene molecules in the composites.

Toughening wood/polypropylene composites with polyethylene octene elastomer (POE)

Polyethylene octene elastomer (POE) as impact modifier was incorporated into wood/polypropylene composites (WPC) to enhance the impact strength of the composite. Two extruding routes, i.e. direct extruding route and two-stage extruding route, were adopted to produce Wood Powder/PP/POE ternary composites. The mechanical and dynamic mechanical analysis (DMA) properties of the composites were investigated. The results showed that the addition of POE can increase the impact strength of the composites, and the composites produced via two-stage extruding route showed superior mechanical properties. The results of the DMA confirmed the mechanical tests.

Physico-Mechanical Responses of Polypropylene-CaCO₃Composite

This study examines some physical and mechanical characteristics of polypropylene (PP) and calcium trioxocarbonate IV (CaCO3) composites prepared by melt blending. The mechanical (tensile strength and impact energy resistance) and physical (density and water absorption capacity) properties of the composites were evaluated using 0% - 40% of the filler. The results showed that 20%-CaCO3 addition improved the ultimate tensile stress by 58%, and the UTS is 84% better when 25%-CaCO3 addition is made while the impact resistance decline by 8 and 12% respectively at these two compositions. In addition, the density only differ from that of pure PP at 25% CaCO3 addition by 18% increment, however, water absorption increased by 400% at 10%-CaCO3 addition.

抗冲共聚聚丙烯性能优化与结构分析

对工艺优化前后的两批抗冲共聚聚丙烯EPS30R产品进行了性能与结构组成研究。对比研究结果表明:优化后的EPS30R冲击强度和弯曲模量均有提高,从结构组成上看,两批EPS30R产品的分子质量及分布基本一致;与EPS30R-1相比,刚韧平衡性更好的EPS30R-2乙烯含量高、橡胶相尺寸更小、分散更均匀,同时其二甲苯可溶物(XS)含量更高且可溶部分特性黏数更高,这些结构特点是使产品冲击性能更高的主要因素;序列结构rr含量低对保持聚丙烯产品刚性有利。

SEBS与β-NAs对PP的协同增韧作用及增韧机理研究

本研究以聚丙烯(PP)为基体、氢化苯乙烯-丁二烯嵌段共聚物(SEBS)和β成核剂(β-NAs)为增韧剂,采用熔融共混法制备了PP/SEBS/β-NAs共混物,研究了SEBS和β-NAs对PP的协同增韧作用并探究了增韧机理。结果表明:当添加20%SEBS和0.05%β-NAs时,得到的PP/SEBS/β-NAs共混物样品的冲击强度达到了76.1 kJ/m2,较纯PP(3.9 kJ/m2)提高了1851.3%。SEBS和β-NAs的协同效应不仅能够增韧PP,还能够提高其加工性能。β-NAs的加入会诱导所得样品的脆-韧转变行为在低SEBS含量下提前发生。增韧机理为,由于β-NAs的加入,PP/SEBS/β-NAs共混物体系中大部分α晶转化为β晶,致使PP晶粒细化,SEBS相尺寸变小、分散更均匀。在外力作用下样品中的SEBS相充当应力集中点,不仅SEBS相内部及SEBS相和PP的界面层会发生空穴化,还会诱导样品中的PP基体发生大量的剪切屈服形变,这些过程会吸收大量能量,赋予PP/SEBS/β-NAs共混物良好的韧性。

iPP/nano-CaCO3/PP-g-GMA复合材料的制备与性能

以等规聚丙烯(iPP)、纳米碳酸钙(nano-CaCO_(3))和甲基丙烯酸缩水甘油酯接枝改性抗冲共聚聚丙烯(PP-g-GMA)为原料,通过熔融共混法制备了iPP/nano-CaCO_(3)/PP-g-GMA复合材料。研究了PP-g-GMA对iPP/nano-CaCO_(3)/PP-g-GMA复合材料力学性能、结晶行为和微观结构的影响,并分析了其增韧机理。结果表明:PP-g-GMA和nano-CaCO_(3)具有协同增韧作用,当两者用量均为40.0质量份时,iPP/nano-CaCO_(3)/PP-g-GMA复合材料23℃时的冲击强度约为纯iPP的6.9倍。PP-g-GMA和nano-CaCO_(3)均具有成核作用,促使基体球晶细化。PP-g-GMA中的橡胶相以球形海岛形式分散在iPP中,起到增韧作用。

注塑条件对抗冲聚丙烯力学性能影响研究

不同的注塑工艺条件会影响聚丙烯微观结构及力学性能,主要研究了注射速率(v)、注射压力(P_(1))、保压压力(P_(2))、保压时间(t)和熔体温度(T)五个参数对高流动抗冲共聚聚丙烯SP531冲击强度和弯曲模量的影响,并分析了注塑条件与力学性能的关系,结果表明:对于高流动SP531,最佳的注塑条件为注射速率30%,注射压力2 MPa,保压压力4 MPa,保压时间40 s,熔体温度200℃。

高流动抗冲聚丙烯EP533N质量优化

根据高流动抗冲共聚聚丙烯EP533N市场质量反馈信息,采取使用新型催化剂-给电子体体系,优化聚合、汽蒸、干燥、挤压等单元的工艺参数,优选复合助剂体系等措施提升产品质量。结果表明,采用新型催化剂体系,工艺参数优化为:流化床反应器中乙烯与乙烯和丙烯混合气的摩尔比降至0.33~0.36,气相反应器内温度升至79~81℃,汽蒸器中蒸汽量升至2000~2200 kg/h,挤压机筒体温度降至200~210℃。优化后,EP533N的弯曲模量达到1327 MPa,冲击强度稳定在9.50 kJ/m2以上,气味等级降至2.85级;产品质量优于市场同类产品,满足市场需求。

无规共聚聚丙烯研究进展

综述了用于生产无规共聚聚丙烯的Ziegler-Natta催化剂和茂金属催化剂的性能及由两种催化剂制备的无规共聚聚丙烯的特点,并总结了近年来关于乙烯-丙烯无规共聚物、丙烯-1-丁烯无规共聚物和其他几种典型的无规共聚聚丙烯产品的聚合机理、聚合工艺及共聚物物理性能的研究进展。

微交联抗冲击间规聚丙烯复合材料制备及其性能研究

利用己内酯与木质素反应制备了改性木质素,将改性木质素、交联剂、硫磺与间规聚丙烯(s PP)共混,通过双螺杆挤出制备了微交联抗冲s PP复合材料。测试了微交联抗冲s PP复合材料的力学性能、流动性和热稳定性等。实验结果表明:当间规聚丙烯、交联剂、改性木质素、硫磺添加份数比例为100/0.2/1.0/0.3时,复合材料的力学性能较好,弯曲最大强度和冲击强度相对纯间规聚丙烯分别提高了11%和116%。

Ballistic Penetration Damage of Hybrid Thermoplastic Composites Reinforced with Kevlar and UHMWPE Fabrics

Polymer matrix types of fiber hybrid composites are key factors to improve ballistic impact damage tolerances.Here we report ballistic penetration damages of Kevlar/ultra-high molecular weight polyethylene(UHMWPE)hybrid composites with thermoplastic polyurethane(PU)matrix.The hybrid composites were penetrated by fragment-simulating projectiles(FSPs)using an air gun impact system.The effects of stacking sequences on the ballistic performance of hybrid composites were analyzed.Two types of specific energy absorption(the energy absorption per unit area density and the energy absorption per unit thickness)were investigated.It was found that the main damage modes of PU hybrid composites were fiber breakage,matrix damage,fiber pullout and interlayer delamination.The instantaneous deformation could not be used as a reference index for evaluating the ballistic performance of the target plate.The energy absorption process of the PU hybrid composites showed a nonlinear pattern.The hybrid structure affected the specific energy absorption of the materials.

高熔体流动速率抗冲共聚聚丙烯的结构与性能研究

为提升高熔融抗冲共聚聚丙烯(IPC⁃J)的刚韧平衡性能,结合抗冲共聚聚丙烯(IPC⁃H)工艺,将IPC⁃J的乙烯含量和乙丙橡胶(EPR)中乙烯含量提高到了12.4%(质量分数,下同)和54%。对IPC⁃J、IPC⁃H、IPC⁃1和IPC⁃2等分别进行了分子链段结构和聚集态表征,结果显示,对比IPC⁃H的微观结构,IPC⁃J的EPR含量从19.4%增至22.8%,重均分子量(Mw)从2.0×10^(5)g/mol减至1.9×10^(5)g/mol,特性黏度(IV)从1.80 dL/g增到1.86 dL/g,分子量分布指数(MWD)从8.9增至10.7,EPR的最大分子量从1.1×10^(6)g/mol增至1.2×10^(6)g/mol;更多的、相对较长的长乙烯结晶链段有助于改善分散颗粒粒径,占比最大的粒径范围从0.3~0.6μm升至0.6~0.9μm;常温和低温冲击强度分别提升至11.0 kJ/m^(2)和5.7 kJ/m^(2)。以300 kt/年聚丙烯生产工艺为基础,在不改变齐格勒⁃纳塔(DQ)型催化剂体系的条件下,通过提高乙烯含量和EPR中乙烯含量实现了高熔融抗冲聚丙烯性能最大优化。