Properties Of Polypropylene Composites Research Articles

Functionalization, compatibilization and properties of polypropylene composites with Hemp fibres

Composites of isotactic polypropylene (PP) with Hemp fibres ( Cannabis sativa), functionalized by means of melt grafting reactions with glycidyl methacrylate (GMA) and prepared by batch mixing, were examined. Either the modification of fibres (Hemp-GMA) and polyolefin matrix (PP- g-GMA), as well as the addition of various compatibilizers (PP- g-GMA, SEBS, SEBS- g-GMA) were carried out to improve the fibre–matrix interactions. The modified components and their composites were characterised by FT-IR analysis, POM and SEM microscopy, RX, DSC, TGA and mechanical tests. The properties of binary (PP/Hemp, PP/Hemp-GMA, PP- g-GMA/Hemp) and ternary (PP/Hemp/compatibilizer) composites were analysed as a function of the fibre amount and compatibilizer content. All modified composites showed improved fibre dispersion in the polyolefin matrix and higher interfacial adhesion when compared to the unmodified system (PP/Hemp) as a consequence of chemical bonding between fibre and polymer. The thermal stability and phase behaviour of the composites resulted to be largely affected by the fibre and matrix modification. Changes in the spherulitic morphology and crystallisation behaviour of PP were observed in the composites due to the nucleating effect of Hemp fibres. Moreover, a marked increase of PP isothermal crystallisation rate (in the range 120–138 °C) was recorded with increasing the Hemp-GMA content. All composites displayed higher tensile modulus (about 2.9 GPa) and lower elongation at break as compared to plain PP; compatibilization with PP- g-GMA (10 phr) resulted in an increased stiffness of the composites as consequence of an improved fibre–matrix interfacial adhesion.

Polypropylene/organoclay nanocomposites compatibilized with hydroxyl‐functional polypropylenes

AbstractThe properties of polypropylene composites can be tailored through the use of nanoclay fillers. The effectiveness of a metallocene‐catalyzed hydroxyl‐functional polypropylene in the compatibilization of polypropylene layered nanosilicate composites was studied, and the results were compared with those for a commercial maleic anhydride functionalized polypropylene. Polypropylene/organoclay nanocomposites were prepared by melt blending, and two polypropylene/compatibilizer/organoclay ratios, 90/5/5 and 70/20/10, were characterized. The organomodification of the clay was carried out with octadecylamine and N‐methylundecenylamine. The structure of the layered silicate was studied by transmission electron microscopy, wide‐angle X‐ray scattering, and small‐angle X‐ray scattering. The fracture surfaces of the composites and thus the efficiency of the compatibilizers to penetrate the galleries of the organoclays were characterized by scanning electron microscopy, and the melt viscosity was studied by stress‐controlled rotational rheometry. The nanostructure was observed with both alkyl amines used for intercalation. The fillers facilitated the processability of all the composites, consisting of equal amounts of compatibilizer and organoclay filler and, in some of the composites, containing twice as much compatibilizer as organoclay filler. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1892–1903, 2005

Interface Modification and Mechanical Properties of Natural Fiber-Polyolefin Composite Products

Natural fibers are potentially a high-performance and non-abrasive reinforcing fiber source. In this study, mechanical properties of polypropylene (PP) composites with various natural fibers such as old newsprint, kraft pulp and hemp were studied. The effect of a low-molecular weight, maleated type coupling agent, on the mechanical properties of these natural fiber-filled PP composites was also investigated and the results showed that this can be used as a good interface modifier for improving the strength properties of the PP-filled composites and the optimum level of the coupling agent was found to be around 3-4 percentage by weight of the composite. Kraft pulp and hemp fiber-filled composites showed better tensile, flexural and un-notched impact strength compared to the glass fiber-filled composites at the same fiber loading. Hybrid composite produced using 10 wt% of glass fiber and 30 wt% of hemp fiber showed only a marginal improvement in the mechanical properties.

Preparation and enhanced properties of poly(propylene)/ silica‐grafted‐hyperbranched polyester nanocomposites

AbstractA series of poly(propylene) silica‐grafted‐hyperbranched polyester nanocomposites by grafting the modified hyperbranched polyester (Boltorn™ H20), possessing theoretically 50% end carboxylic groups and 50% end hydroxyl groups, which endcapped with octadecyl isocyanate (C19), onto the surface of SiO2 particles (30 nm) through 3‐glycidoxy‐propyltrimethoxysilane (GPTS) was prepared. The effect of silica‐grafted‐modified Boltorn™ H20 on the mechanical properties of polypropylene (PP) was investigated by tensile and impact tests. The morphological structure of impact fracture surface and thermal behavior of the composites were determined by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), respectively. The melt viscosity of composites was investigated by melt flow index (MFI). The obtained results showed that: (1) the modified Boltorn™ H20 was successfully grafted onto the SiO2 surface confirmed by FT‐IR and X‐ray photoelectron spectroscopy (XPS) analysis; (2) the incorporation of silica‐grafted‐modified Boltorn™ H20 (3–5 wt% SiO2) greatly enhanced the notched impact strength as well the tensile strength of the composites; (3) the incorporation of silica‐grafted‐modified Boltorn™ H20 had no influence on the melting temperature and crystallinity of PP phase; (4) the MFI of PP composites increased when the silica‐grafted‐modified Boltorn™ H20 particles were added compared with PP/SiO2 or PP/SiO2‐GPTS composites. Copyright © 2004 John Wiley & Sons, Ltd.

Effect of nano‐Mg(OH)2 on the mechanical and flame‐retarding properties of polypropylene composites

AbstractNano‐Mg(OH)2 was synthesized with an in situ deposition technique, and its size was confirmed by X‐ray diffraction. A polypropylene–Mg(OH)2 composite was prepared by melt‐extrusion processing. The addition of a small quantity of a nanofiller (up to 10 wt %) increased Young's modulus up to 433% with respect to the modulus of virgin polypropylene. The addition of up to 4 wt % Mg(OH)2 produced the maximum increase, and a further decrease in the tensile strength was observed with an increase in the concentration of nano‐Mg(OH)2. Increases in the hardness and other properties were due to higher nucleation and the intercalation of polymer chains in the nanolayer galleries. The flame‐retarding property was demonstrated by the rate of burning. The time required to burn the nanofilled composite was greater than the time required for virgin polypropylene. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 116–122, 2004

Mechanical properties of polypropylene composites reinforced with long glass fibres and mineral fillers

The mechanical behaviour of long discontinuous glass fibre (LGF) reinforced polypropylene (PP) composites filled with talc or calcium carbonate fillers was studied. Sample specimens were processed by injection moulding, after which tensile and impact properties were analysed. In addition, scanning electron microscopy was used to analyse the morphology of the fracture surfaces. The results showed that the use of talc as a hybrid filler in LGF reinforced PP leads to a better tensile strength and toughness than in a corresponding hybrid composite based on calcium carbonate. Furthermore, it was observed that the matrix had a dominant role at low fibre content, whereas at high fibre loading, the effect of fibres was more evident.

The effect of interfacial interactions on the mechanical properties of polypropylene/natural zeolite composites

Abstract The effect of interfacial interactions on the mechanical properties of polypropylene (PP)/natural zeolite composites was investigated under dry and wet conditions. Interfacial interactions were modified to improve filler compatibility and mechanical properties of the composites by surface treatment of natural zeolite with a non-ionic surface modifier; 3 wt% polyethylene glycol (PEG) and three different types of silane coupling agents; 3-aminopropyltriethoxysilane (AMPTES), methyltriethoxysilane (MTES) and 3-mercaptopropyltrimethoxysilane (MPTMS), at four different concentrations (0.5–2 wt%). PP composites containing (2–6 wt%) zeolite were prepared by an extrusion technique. The tensile properties of the composites determined as a function of the filler loading and the concentration of the coupling agents were found to vary with surface treatment of zeolite. Silane treatment indicated significant improvements in the mechanical properties of the composites. According to the dry and wet tensile test results, the maximum improvement in the mechanical properties was obtained for the PP composites containing 1 wt% AMPTES treated zeolite. The improvement in the interfacial interaction was confirmed using a semi-empirical equation developed by Pukanszky. Good agreement was obtained between experimental data and the Pukanszky model prediction. Scanning electron microscopy studies also revealed better dispersion of silane treated filler particles in the PP matrix.

Correlation of the material properties of calcium carbonate filled polypropylene with the filler surface energies

AbstractThe physical and mechanical properties of polypropylene (PP) were measured and compared with those of PP composites filled with calcium carbonate modified with sodium polyacrylate, stearic acid, or both. The variations in the mechanical properties showed a high degree of correlation with the surface energies of the fillers, as determined by inverse gas chromatography. The results confirmed the usefulness of inverse gas chromatography for characterizing the compatibility of polymer–filler combinations. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1951–1955, 2003

Effect of surface modification of glass wool on the mechanical and electrical properties of polypropylene/modified glass‐wool composites

AbstractThe surface of glass wool (GW) was modified by two different methods, either by grafting methyl acrylate (MA) onto GW in the presence of potassium persulfate (PPS) as initiator, or by adsorbing stearic acid (AS) as surface active agent onto the GW surface. It was found that conversion and grafting yield of poly(methyl acrylate) (PMA) onto the GW surface increased with increasing initiator concentration, whereas by modifying the GW surface by adsorption of SA, the adsorption of SA was found to be high at small values of equilibrium concentrations and two distinct plateau regions were observed. Mechanical and electrical properties of polypropylene (PP) sheets loaded with modified GW were measured. The obtained data showed that the presence of PMA as grafted polymer onto the GW surface has a plasticizing effect on the prepared PP composites. On the other hand, SA, as a surface modifier for GW, acts as a reinforcing agent for the formed PP composites, which have very good dielectric properties. From the obtained results, one can deduce that the prepared PP/GW composites have promising dielectric properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1061–1069, 2002

Processing and properties of polypropylene composites with high filler content

The effects of repetitive injection molding cycles at different temperatures and shear rates on the structure and mechanical properties of unfilled and talc-filled polypropylene were studied. The main effect of reprocessing in both materials is a decrease in molecular weight of the polymeric matrix, which is more marked and concomitant with breaking of particles at high shear levels. The chemical structure, however, remains unchanged.The observed degradation processes only slightly affect the crystalline behaviour and the small strain properties of the materials studied. However, the break properties are affected, their decrease depends on the filler content and they appear more sensitive to high shear level than to high processing temperatures.

Processing and Properties of Polypropylene Composites with High Filler Content

Highly filled polypropylene composites have been prepared with filler contents up to 43.8 vol.% (70 wt.%) after surface treatment of the fillers with titanate or silicone. The fillers used were calcium carbonate, talc and barium sulfate. Surface modification of the fillers facilitated extrusion and reduced brittleness while providing hard composites with high density. The high density and hardness provide a texture which is not characteristic of polypropylenes, but more like thermoset composites or ceramics; yet the composites can be extruded using typical thermoplastic processing equipment. The composition has been measured by thermogravimetry, and morphology observed with scanning electron microscopy. The tensile properties were measured and related to the composition, filler type and surface treatment.

THERMAL CONDUCTIVITY OF THERMOPLASTIC COMPOSITES WITH SUBMICROMETER CARBON FIBERS

This is an experimental study of the thermal properties of polypropylene composites reinforced with aligned Pyrograf III™ vapor-grown carbon fiber. The fiber reinforcement was uniaxially aligned in the composite samples by an extrusion process, thereby producing improved properties along the preferred direction. The density, specific heat, and thermal diffusivity were determined experimentally and used to calculate the thermal conductivity in both the longitudinal and transverse directions of the test specimens. The experimental thermal conductivity results were then compared with those predicted by the Lewis and Nielsen semitheoretical model to evaluate the axial thermal conductivity of the Pyrograf III fiber.

Structure development and properties of PET fibre filled PP composites

The structure development and mechanical properties of polypropylene (PP) composite containing polyethylene terephthalate (PET) fibres were studied both in the presence and absence of a compatibilizer such as maleic anhydride (MA). The structural and morphological studies were carried out by WAXD, optical microscopy and SEM techniques. In the absence of MA, the PET fibres in PP showed transcrystalline morphology and thus proved to be a strong nucleating agent for PP spherulites. On the other hand, in the presence of MA, no transcrystalline growth of PP was observed on the surface of PET fibres. The fibre to matrix bonding was better in presence of MA than without it, as was revealed by SEM of fractured surfaces. The mechanical properties viz. impact strength and tensile modulus showed enhancement for these composites as compared to pure PP. However, pronounced increase in the properties was seen for PET fibres filled PP composite without MA. The above findings could be understood in terms of high aspect ratio for PET fibres, transcrystalline morphology, good fibre–matrix adhesion and nucleating ability of PET fibres in PP matrix.

Flammability of Composites Based on Polypropylene and Flax Fibers

Biodegradability and interesting physical and mechanical properties of polypropylene (PP)/cellulose composites are the essential motive for undertaking fundamental studies of various properties of such materials. An addition of lignocellulosic particles to polymers results in a change in properties of the product obtained which is a resultant of properties of lignocellulosic material and those of polymer and depends on the proportion of both materials. It is also reflected in the flammability characteristics of the composites. In this study we have analyzed flammability of PP composites with long flax fibers obtained by compressing. The amounts of natural fibers were 12.5%, 20%, 30% and 40%. The thickness of the investigated samples was 5 mm. The samples were tested in accordance with ISO 5660 (Cone Calorimeter) at heat flux of 35 kW/m2. Heat release rate (HRR) and mass loss rate (MLR) curves show that thermal decomposition and combustion of the mentioned samples occur in a different way. When flax fiber content was 12.5%, a reduction in maximum heat released (HRR peak) by about 35% was observed. However, time to sustained ignition of composites was shorter than that of PP. The characteristics of the composite are closer to those of lignocellulosic material. The addition of 12.5% fibers resulted in an increase in fire retardancy of the composite compared to polypropylene alone. The addition of fibers in the amount exceeding 20% made the composite material characteristics similar to those of lignocellulosic materials.

Influence of the physical structure of flax fibres on the mechanical properties of flax fibre reinforced polypropylene composites

This study investigates the influence of the physical structure of flax fibres on the mechanical properties of polypropylene (PP) composites. Due to their composite-like structure, flax fibres have relatively weak lateral bonds which are in particular present in flax fibres that are often used in natural fibre mat reinforced thermoplastics (NMT). These weak bonds can be partly removed by combing the fibres. In order to study the influence of the physical structure of flax fibres on NMT tensile and flexural properties, uncombed and combed flax fibre reinforced PP composites were manufactured via a wet laid process. The influence of improved fibre-matrix adhesion was studied using maleic-anhydride grafted PP. Results indicated that the flax physical structure has a significant effect on flax-PP composite properties and that the flax fibre reinforced PP properties are similar to values predicted with existing micromechanical models. The tensile modulus of flax-PP composites can fairly compete with commercial glass mat reinforced thermoplastic (GMT) modulus, the strength, however, both tensile and flexural, can not. In order to rise the strength of flax fibre reinforced PP composites to the level of GMT strength, the flax fibres have to be further isolated to elementary flax fibres.

Effect of glass filler surface treatment on flexural properties of polypropylene composites

The effect of glass particle surface treatment on the flexural properties of glass particle reinforced polypropylene composites was investigated. The glass particles used were glass beads, glass milled fibers (average length 26 μm), and glass cut fibers (average length 100 μm). The glass particles were treated with six kinds of silane coupling agents with different organic functional groups. The wettability of glass plates treated with these coupling agents was also estimated by measurement of contact angles using thirteen liquids. It was found that composite flexural properties correlated with wettability of the glass plate when both the glass particles and glass plate were treated with the same coupling agent. For the case where the organic functional group comprised an alkyl group, the composite flexural rigidity and strength decreased with increasing critical surface tension calculated from the contact angles of halogen-containing liquids.

Influence of molding conditions and talc content on the properties of polypropylene composites

Abstract Polypropylene composites with several talc contents were injection molded under different processing conditions. DSC, density and SEM were used to characterize the materials. Melt flow index, DSC and tensile tests were carried out to study the properties of the composites. Both the nucleation effect of talc and most of the thermal properties, except the MFI, did not depend greatly on the talc content or the processing conditions. The adhesion level was poor as often seen in unmodified composites. The variation of the tensile properties with filler content was compared with that predicted by the most characteristic models. Among the processing conditions, both the mold and the melt temperature were found to be the most important parameters in the ranges studied. The former through densification of the amorphous PP phase at high mold temperature, and the latter probably through improved homogenization at high melt temperature.

Processing and Properties of Polypropylene Composites*This paper was presented at the National Research Council, Canada, Composites '96 and Oriented Polymers Symposium Proceedings

Processing and Properties of Polypropylene Composites*This paper was presented at the National Research Council, Canada, Composites '96 and Oriented Polymers Symposium Proceedings

High TC superconductor polymer composite based on YBa2Cu3O7−x. II. Conduction mechanisms and temperature effect on conductive and dielectric properties of polypropylene composites

AbstractTo improve the connectivity of YBaCuO particles in a polypropylene matrix, different amounts of carbon black (N) or copper (C) were incorporated into the binary base system. In this research the effects of these conductor fillers on the conduction mechanism of the experimental composites were studied using complex impedance spectroscopy as the analytical technique. In addition the effects of temperature on certain electrical properties were examined in the synthesized materials. © 1995 John Wiley & Sons, Inc.

Multistage wet grinding of talc: relation between physico-chemical parameters of the filler and mechanical properties of filled polypropylenes

Three talc samples of different mineralogical composition were wet-ground with an increasing number of grinding cycles. On each sample the particle size analysis, X-ray diffraction spectra, infrared spectra and nitrogen adsorption isotherms were carried out. In parallel, three mechanical properties of talc-filled polypropylenes were determined. A statistical analysis based on normalized principal component analysis and multiple partial linear regression was then carried out in order to determine correlations between the physico-chemical parameters of the fillers and the mechanical properties of polypropylene composites. The results show that this approach is valid only if the samples are separated according to their mineralogical composition. On the basis of this first analysis, an “industrial” model based on easily obtainable parameters is proposed. It is very satisfactory for talc-rich samples. For more chloritic ores, some other parameters have to be measured to enhance the quality of the models. The approach proposed in the present study seems then very promising.