SAXS investigation of structure–property relationship of polypropylene/montmorillonite composites during load cycling

Polypropylene (PP) can hardly be reinforced by the layered silicate montmorillonite (MMT), but the material fatigue appears somewhat reduced. The probable reason is amplified competitive nucleation of the PP by MMT component. Utilizing small‐angle X‐ray scattering (SAXS) from synchrotron, we investigate the nanostructure evolution of the PP in straining experiments from neat PP and compatibilized composite materials. The compatibilizer is a styrene–ethylene/butylene–styrene copolymer (SEBS). Oriented injection‐molded test bars are studied. The discrete SAXS probes variations of sizes and distances among those crystalline domains that are not placed at random. Crystallite dimensions and distances are documented for modeling purposes. The nanoscopic strain is computed from the distance variation and compared with the macroscopic strain. Differences between macroscopic and nanoscopic strain are observed. They require postulating regions with statistical placement of crystallites (poorly arranged region, PAR) in addition to the SAXS‐probed well‐arranged semi‐crystalline entities (WAE). The extensibility of WAEs must be different from that of the PARs. In neat PP, the observed WAEs are well developed and stronger than the PARs. In the composites, the WAEs are made from thin and less extended crystalline domains. They are weaker than the PARs that appear reinforced. Thus, enclosing each MMT layer a PAR is formed, and the WAEs generated farther away remain imperfect. Consequently, in the composites, the narrow crystalline domains from the WAEs do not break into even smaller pieces, and the fatigue of the composites is lower than that of the neat PP. Copyright © 2013 John Wiley & Sons, Ltd.     

双功能催化体系制备聚丙烯/蒙脱土复合材料

为了制备聚丙烯/蒙脱土纳米复合材料,将Brookhart型的乙烯齐聚催化剂负载于有机蒙脱土片层间,进一步与丙烯聚合茂金属催化剂进行复配得到双功能催化体系。采用这种双功能催化剂体系通过催化乙烯齐聚得到α-烯烃/蒙脱土的齐聚产物,进一步将丙烯与这种齐聚产物共聚,合成了一系列结构不同的聚丙烯/蒙脱土纳米复合材料。通过气相色谱、X射线衍射(XRD)分析得出蒙脱土负载的铁系催化剂催化乙烯齐聚产物是以C_4~C_(16)为主的α-烯烃,蒙脱土以片层形式分散于齐聚产物的甲苯溶液中。研究了蒙脱土负载的铁系催化剂与共聚催化剂复配催化乙烯齐聚以及丙烯与齐聚产物共聚合的情况。通过XRD、透射电镜、差示量热分析、凝胶渗透色谱分析表征可知,蒙脱土以纳米片层剥离的形式均匀分散于聚丙烯基体中,聚丙烯/复合材料的结晶温度比纯聚丙烯有所下降,所得聚丙烯基体分子量在8.1×10~4~17.1×10~4g/mo L。     

Thermophysical properties of polypropylene/aluminum composites

This article is dedicated to the study of the thermal parameters of composite materials. A nonlinear least‐squares criterion is used on experimental transfer functions to identify the thermal conductivity and the diffusivity of aluminum‐polymer composite materials. The density measurements were achieved to deduce the specific heat and thereafter they were compared to values given by differential scanning calorimetry measurement. The thermal parameters of the composite material polypropylene/aluminum were investigated for the two different types of aluminum filler sizes. The experimental data were compared with several theoretical thermal conductivity prediction models. It was found that both the Agari and Bruggeman models provide a good estimation for thermal conductivity. The experimental values of both thermal conductivity and diffusivity have shown a better heat transport for the composite filled with large particles. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 722–732, 2004     

Thermal characterization of polypropylene/vermiculite composites

Vermiculite clay (VMT) was organically modified with a quaternary organic salt and added to polypropylene (PP). The compounds were prepared by melt intercalation using a twin extruder. The morphology of the composites was investigated through wide-angle X-ray diffraction (WAXD). The WAXD results suggested that exfoliation phenomena were found for the composites with modified clay. The thermal properties of the obtained composites were studied by means differential scanning calorimetry (DSC) and thermogravimetry (TG) measurements. A variation in the crystallinity of PP was found. A significant increase of the thermal stability of PP was achieved in the presence of the modified VMT.     

Toughness mechanism of polypropylene/elastomer/filler composites

The toughening mechanisms of polypropylene filled with elastomer and calcium carbonate (CaCO₃) particles were studied. Polypropylene/elastomer/CaCO₃ composites were prepared on a twin‐screw extruder with a particle concentration of 0–32 vol %. The experiments included tensile tests, notched Izod impact tests, scanning electron microscopy, and dynamic mechanical analysis. Scanning electron microscopy showed that the elastomer and CaCO₃ particles dispersed separately in the matrix. The modulus of the composites increased, whereas the yield stress decreased with the filler concentration. The impact resistance showed a large improvement with the CaCO₃ concentration. At the same composition (80/10/10 w/w/w), three types of CaCO₃ particles with average diameters of 0.05, 0.6, and 1.0 μm improved the impact fracture energies comparatively. The encapsulation structure of the filler by the grafting elastomer had a detrimental effect on the impact properties because of the strong adhesion between the elastomer and filler and the increasing ligament thickness. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1113–1123, 2005     

Isothermal crystallization kinetics of polypropylene/POSS composites

Polypropylene (PP)/octavinyl polyhedral oligomeric silsesquioxane (POSS) composites were prepared by two different processing methods: reactive blending and physical blending, and the crystallization behavior of PP and PP/POSS composites was studied by means of differential scanning calorimetry and polarized optical microscope. The results showed that the crystallization of PP in PP/POSS composites was strongly influenced by the different processing methods. POSS particles can act as effective nucleating agent, accelerating the crystallization of PP. The crystallization rate increased more dramatically for the reactive blending composite due to the stronger nucleating effect of PP grafted POSS. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1762–1772, 2008     

Accelerated weathering of polypropylene/wood flour composites

Wood-plastic composites (WPCs) have received increasing attention during the last decades, because of many advantages related to their use. Some of their main applications are represented by outdoor furnishing and decking; therefore, it is important to assess their behaviour under UV exposure. In this work, polypropylene/wood flour composites were prepared and their resistance to photooxidation investigated. The composites were prepared by extrusion and compression moulding, and were subjected to mechanical tests, FTIR analysis and molecular weight measurements. The results showed that the composites retained a higher fraction of the original mechanical properties after accelerated weathering; the wood flour did not significantly degrade throughout the irradiation time slot of the investigation and the composites kept a higher percentage of the original molecular weight.     

Effect of silane‐grafted polypropylene on the morphology of polypropylene and nylon 6/clay composites

Polypropylene (PP)/nylon 6/clay composites were prepared by compounding of PP, which had previously been treated with two kinds of silane compounds, with a master batch composed of 90 wt % of nylon 6 and 10 wt % of octadecyl amine‐modified sodium montmorillonite (NM10). The morphology of the composites was investigated by means of SEM, TEM, XRD, and energy‐dispersive X‐ray analysis. All of the composites exhibited a phase‐separated morphology, irrespective of whether the PP was modified with the silane compounds or not. However, adhesive strength between the modified PP and NM10 was stronger than that between neat PP and NM10. Moreover, the PP grafted with 3‐(trimethoxysilyl)propyl methacrylate (PP2) reacted with the silanol groups of the clay to form PP‐clay hybrid during the compounding, which acted as a compatibilizer for the PP/nylon 6/clay composite. PP2NM composite (PP2/NM10 80/20 on weight basis) exhibited a peculiar morphology, in that the PP‐rich phase formed island domains within the nylon 6‐rich domains, which were in turn dispersed in the PP‐rich continuous matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 607–615, 2007.     

Ethylene–acrylic acid copolymer induced electrical conductivity improvements and dynamic rheological behavior changes of polypropylene/carbon black composites

The experimental data reveal that the addition of ethylene–acrylic acid copolymer (EAA) into carbon black (CB)/polypropylene (PP) composites can improve the electrical conductivity of CB/PP composites by two to six orders of magnitude at a comparatively low CB content (φ), and when φ = 2.5 vol %, 60/40 of PP/EAA is an optimum for electrical conductivity improvement. The dynamic rheological data show that with increasing φ there are apparent rheological percolations for CB/PP composites. A modified Kerner–Nielson equation can be used to describe the correlation between electrical percolation and dynamic viscoelastic percolation. The addition of EAA into CB/PP composites leads to apparent changes in dynamic rheological behaviors. When φ = 2.5 vol %, a rheological percolation appears in CB/PP/EAA (CPE) composites with increasing EAA content. The similar rheological behaviors correspond to the similar morphological structures for CPE composites with φ = 5.0 vol %. The appearance of bumps in the van‐Gurp–Palmen plots corresponds to the formation of network structure in CB/PP and CPE composites, and the more perfect the networks, the higher the amplitude of the bumps. All data indicate that the van‐Gurp–Palmen plot is sensitive to the formation of filler particle networks or cocontinuous phase which spans the whole composite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1762–1771, 2009     

Emission of possible odourous low molecular weight compounds in recycled biofibre/polypropylene composites monitored by head-space SPME-GC–MS

A disadvantage of the use of natural fibres to reinforce polypropylene is their poor thermal stability, which results in their degradation at processing temperatures of the composites. As a result of this, there is a formation of low molecular weight compounds that are responsible for undesirable odours. Head-space-solid phase microextraction (HS-SPME) was used as a sample preparation technique and gas chromatography–mass spectrometry (GC–MS) was used to identify the low molecular weight compounds in natural polypropylene/polypropylene composites after simulating degradation. Among the compounds found in the samples, there are fragments of PP chains as heptadecane, compounds from antioxidants such as 2,4-bis(1,1-dimethylethyl)-phenol, and p-tert-butylphenol, and compounds from biofibres ageing, such as ethylparaben and vanillin. Numerous carboxylic acids were also identified, being these most probably the source of the undesirable odours.     

Effect of the interfacial interaction on the phase structure and rheological behavior of polypropylene/ethylene– octene copolymer/BaSO4 ternary composites

In polypropylene (PP)/ethylene–octene copolymer (POE)/BaSO₄ ternary composites, two different kinds of phase structures are assumed:(1) POE and BaSO₄ filler are separately dispersed in the PP matrix and (2) POE‐encapsulated filler particles (core–shell structure) are dispersed in the matrix. This depends on the interfacial interaction of the composites. For the design of composites with different interfacial interactions, three routes for the preparation of BaSO₄ master batches were developed. First, a mixture of BaSO₄, POE, and maleic anhydride (MAH) in a certain ratio was extruded in the presence of dicumyl peroxide and then pelletized. In extrusion, MAH‐functionalized POE was in situ formed to enhance the interfacial interaction between POE and BaSO₄. Second, a mixture of POE and BaSO₄ was directly extruded and then pelletized. Third, after BaSO₄ was treated with an organic titanate coupling agent, the treated BaSO₄ and POE were blended in extrusion and then pelletized. Scanning electron microscopy observations showed that the core–shell structure in which POE encapsulates BaSO₄ particles is formed through route 1, whereas POE and BaSO₄ are separately dispersed into the PP matrix through routes 2 and 3. The rheological behavior of PP/POE/BaSO₄ ternary composites was studied with a controlled stress rheometer. The results showed that the interfacial interaction in composites with core–shell morphology is the strongest. Interparticle interactions give rise to the formation of interparticle networks; the stronger the network is, the larger the shear yield stress is and the smaller the thixotropic loop area is. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1804–1812, 2002     

Influence of fabric geometry on yarn pull‐out property and wear performance of hybrid S‐glass/PTFE fabric‐reinforced composites

The friction states between yarns affect the stress transferred in fabric and the fabric structure significantly affects the tribological properties of composites. In this aricle, the effects of fabric structure on yarn pull‐out property and tribological performance of composite were thoroughly studied. Four different fabrics with same tissue cycles number and thread count (2/2 double twills, 1/3 twill, 4‐shaft satin, and 4‐shaft reinforced satin) were used to evaluate the yarn pull‐out property in fabric and the tribological performance of corresponding composites. The results indicate that fabric structure has a significant effect on the yarn pull‐out property in fabric. In particular, the yarn pull‐out property of 4‐shaft reinforced satin was best in the four fabrics structure used in this article owing to the excellent integrity of the 4‐shaft reinforced satin fabric structure and the distribution characteristics of the fabric intersection points. The tribological performance of the 4‐shaft reinforced satin fabric enhanced composites were positively correlated with yarn pull‐out property because the yarn pull‐out property in fabric played an important role in energy dissipation and load carry capacity.     

The processing and properties of conductive polypropylene/polypyrrole composites

Polypropylene (PP) particles were chemically coated with polypyrrole (PPy). The content of polypyrrole varied from 0.8 to 7.6 wt.-%. Electrical conductivity of compression moulded samples depends on the concentration of polypyrrole and reached values from 4×10⁻¹⁰ to 5×10⁻³ S/cm, which is about 7 orders of magnitude higher than the conductivity in the blends prepared by mechanical mixing of PP and PPy in the same PPy concentration range. Highly conductive composites were also obtained from a mixture of coated and non-coated PP particles. The PP/PPy composites were characterized by elemental analysis, SEM and mechanical testing. The antistatic properties of PP/PPy composites were demonstrated. The electrical and mechanical properties depend on processing of composites.     

Rheological behavior of polypropylene/octavinyl polyhedral oligomeric silsesquioxane composites

The reactive blending composites of isotactic polypropylene (PP)/octavinyl polyhedral oligomeric silsesquioxane (POSS) were prepared in the presence of dicumyl peroxide. Comparison of the rheological behavior of physical and reactive blending composites was made by oscillatory rheological measurements. It was found that the viscosity of physical blending composites drops at lower POSS content (0.5–1 wt %) and thereafter increases with increasing POSS content; that of reactive blending composites increases with increasing POSS content and displays a solid‐like rheological behavior at low frequency region when POSS content is higher than 1 wt %. The deviation of reactive blending composites from the scaling log G′–log G″ of linear polymer in Han plot, upturning at high viscosity in Cole–Cole plot, and from van Gurp–Palmen plot are related to the gelation behavior reactively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 526–533, 2008     

Rigidity analysis of polypropylene/vegetal fibre composites after recycling

Polypropylene/hemp or sisal fibre composites exhibit interesting recyclability [Bourmaud A, Baley C. Investigations on the recycling of hemp and sisal fibre-reinforced polypropylene composites. Polymer Degradation and Stability 2007;92(6):1034-45]. The obtained results prove that the tensile modulus of these polypropylene/vegetal fibre composites is well conserved with the number of reprocessing cycles. In this work, we investigated the relationship between the mechanical properties of the fibres and those of the composites by taking the influence of the recycling into account.In the first part of this study we carried out nanoindentation and tensile tests on vegetal fibres to obtain transversal and longitudinal Young's moduli. The experimental values were then introduced into micromechanical models, taking the aspect ratio changes into account, to estimate the stiffness of the PP/vegetal fibre injected composites before and after recycling. The first results show an interesting correlation between experimental results and model predictions; however a general underestimation of tensile stiffness of composites can be noticed.     

Brittle–ductile transition of polypropylene/ethylene–propylene–diene monomer blends induced by size,temperature, and time

To study the brittle–ductile transition (BDT) of polypropylene (PP)/ethylene–propylene–diene monomer (EPDM) blends induced by size, temperature, and time, the toughness of the PP/EPDM blends was investigated over wide ranges of EPDM content, temperature, and strain rate. The toughness of the blends was determined from the tensile fracture energy of the side‐edge notched samples. The concept of interparticle distance (ID) was introduced into this study to probe the size effect on the BDT of PP/EPDM blends, whereas the effect of time corresponded to that of strain rate. The BDT induced by size, temperature, and time was observed in the fracture energy versus ID, temperature, and strain rate. The critical BDT temperatures for various EPDM contents at different initial strain rates were obtained from these transitions. The critical interparticle distance (ID_c) increased nonlinearly with increasing temperature, and when the initial strain rate was lower, the ID_c was larger. Moreover, the variation of the reciprocal of the initial strain rate with the reciprocal of temperature followed different straight lines for various EPDM contents. These straight lines were with the same slope. Furthermore, a diagram at critical BDT points in three dimensions (ID, T, and initial strain rate) was given for the PP/EPDM blends. The brittle and ductile zones are clearly shown in this diagram. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1433–1440, 2004     

Annealing induced electrical conductivity jump of multi‐walled carbon nanotube/polypropylene composites and influence of molecular weight of polypropylene

Multi‐walled carbon nanotube (MWCNT)/polypropylene (PP) composites were prepared by a micro melt mixing process. As‐prepared composites had relatively low electrical conductivity due to the disruption of MWCNT network by strong shear. The electrical conductivity jumped to high values throughout an annealing process above the melting temperature of PP. The significant enhancement of electrical conductivity was influenced by annealing time, temperature, and content of MWCNTs. In particular, molecular weight of PP played an important role in affecting the conductivity enhancement. The molecular weight of PP was varied from 190,000 to 340,000 to examine its effect on the electrical conductivity. By comparing the conductivity enhancement behavior of composites with different molecular weight PPs and observing the morphology evolution during annealing, it was found that reaggregation of MWCNTs and the subsequent formation of MWCNT network during annealing are the main reasons for the jump of electrical conductivity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Natural source compatibilizers for olive waste/recycled polypropylene matrix composites

A simple, environmentally friendly process was developed for surface hydrophobization of cellulose-rich waste to improve their compatibility with recycled polypropylene (rPP), helping reduce costs while recycling environmentally problematic waste such as solid olive waste (also called olive pomace). In this study, an improvement of the interfacial bonding strength between the hydrophilic waste particles and the hydrophobic matrix was achieved by surface hydrophobization of the waste using a ring-opening polymerization reaction of epoxidized soy-bean oil (ESBO) with SnCl₂ as a catalyst. The treatment on cellulose based filter paper led to a contact angle of 128°. The composite containing treated olive pomace has shown an increase in the elongation of 92% and an increase in the stress at yield of 15%, indicating improved compatibility.