Rice husk/poly(propylene‐co‐ethylene) composites: Effect of different coupling agents on mechanical,thermal, and morphological properties

Poly(propylene‐co‐ethylene) composites with rice husk were prepared in a corotating intermeshing twin‐screw extruder using four different coupling agents. While modified maleic anhydrides such as maleated polypropylene (MAPP) and maleated polyethylene (MAPE) are commonly used as compatibilizers to improve interfacial adhesion between lignocellulosic filler and matrix, in this study, polypropylene grafted with acid comonomer (CAPP) and high‐density polyethylene grafted with acid comonomer (CAPE) were also used. The morphologies and the thermal and mechanical properties of the composites were characterized using scanning electron microscopy, thermogravimetric analysis, differential scanning analysis, tensile and impact tests. The results indicate that the base resin of the compatibilizer is an important factor in determining the effectiveness of compatibilizers for composites. Composites with PP‐based compatibilizers are more effective than PE‐based compatibilizers due to the improved wetting of the former compatibilizer in the matrix polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Tensile properties and stress whitening of polypropylene/polyolefin elastomer/magnesium hydroxide flame retardant composites for cable insulating application

Flame retardant polypropylene (PP) composites were prepared by combining random polypropylene with uncoated and surface‐treated forms of magnesium hydroxide filler and elastomeric modifiers, with and without maleic anhydride functionalization. Four types of magnesium hydroxide (MDH) with different surface treatments were compounded at amounts up to 60% by weight to PP/polyolefin elastomer (POE) matrix resin to obtain a series of composites. The tensile strength and elongation at break were measured. MDH coated with polymeric material was found to give a high elongation at break value compared with the values obtained with uncoated and vinyl silane and amino silane coated MDH. Two types of POE, i.e., neat and maleic anhydride grafted POE (POEgMA), were used to investigate the stress whitening of composites in bending deformation. POEgMA used composites showed no stress whitening while neat POE used composites showed whitening when bended. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2311–2318, 2005     

Steam-exploded wheat straw fibers as reinforcing material for polypropylene-based composites. Characterization and properties

Composites of wheat straw fibers with polypropylene (iPP) and maleic anhydride modified polypropylene (iPPMA) were prepared. Before being mixed with polypropylene matrices, the wheat straw fibers were subjected to a steam explosion process that induces morphological and structural changes in lignocellulosic materials. Such changes are able to enhance the interactions with the thermoplastic matrix. Compared with iPP, the modified matrix (iPPMA) has shown higher mechanical performances (tensile and impact behavior) and a remarkable decrease of water absorption, that is one of the main drawbacks of natural fiber composites. Finally, the presence of covalent bonds between maleic anhydride and steam-exploded (STEX) fibers, by means of an esterification reaction, produced during the melt-mixing process, can explain the resulting good interfacial adhesion found in iPPMA-based composities.     

An investigation on the mechanical and dynamic rheological properties of single and hybrid filler/polypropylene composites based on talc and calcium carbonate

Some results of experiments on the mechanical and rheological properties of mineral filled polypropylene were presented. Single filler and hybrid filler composites of talc and calcium carbonate (CaCO₃) were prepared in a co‐rotating twin‐screw extruder. The effect of filler type, filler content, and coupling agent on the mechanical and rheological properties of the polypropylene were studied. The coupling agent was maleic anhydride‐grafted polypropylene (PP‐g‐MA). It was found that the mechanical properties are affected by filler type, filler concentration, and the interaction between filler and matrix. The tensile strength of the composite is more affected by the talc while the impact strength is influenced mostly by CaCO₃ content. The elongation at break of PP/CaCO₃ composites was higher than that of PP/talc composites. The incorporation of coupling agent into PP/mineral filler composites increased the mechanical properties. Rheological properties indicated that the complex viscosity and storage modulus of talc filled samples were higher than those of calcium carbonate filled samples while the tan δ was lower. The rheological properties of hybrid‐filler filled sample were more affected by the talc than calcium carbonate. The PP‐g‐MA increased the complex viscosity and storage modulus of both single and hybrid composites. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Performance of expanded graphite and expanded milled‐graphite fillers in thermosetting resins

Epoxy/expanded graphite (EG) and polyester/EG composites were prepared with the aid of sonication, while epoxy/expanded‐milled graphite (epoxy/milled‐EG) and polyester/expanded‐milled graphite (polyester/milled‐EG) composites were prepared on a three‐roll paint mill. The epoxy/EG and polyester/EG composites exhibit a sharp insulator/semiconductor transition at markedly low percolation thresholds, due to the vermicular shape of EG having high aspect ratio and surface area. The morphologies of epoxy and polyester resins incorporated with EG and milled‐EG fillers were observed by scanning electron microscopy (SEM). The results of dynamic mechanical analysis of the composites reveal that both EG and milled‐EG fillers increase the T_g of the epoxy matrix. Milled‐EG increases the G′ of the epoxy matrix, while EG decreases the G′ of the epoxy matrix, due to the existence of abundant pores in EG. The milled‐EG filler has the same effect on the polyester matrix as on the epoxy matrix, but the EG filler has no significant effect on the mechanical properties of polyester matrix. POLYM. COMPOS., 26:526–533, 2005. © 2005 Society of Plastics Engineers     

Disappearance of the filler—An interesting interfacial evolution during the photooxidative aging of polypropylene composites

The interface between the matrix and filler in polyolefin composites plays an important role in their photooxidative aging processes. An interesting phenomenon, the gradual disappearance of filler particles was observed during the early natural aging of polypropylene (PP)/CaCO₃ composites. Similar phenomena were also observed in a PP/SiO₂ composite and PP/poly(methyl methacrylate) blend. The morphological observation and tensile and chemical analyses indicated that the photooxidized groups of the PP chain interacted strongly with the filler particles; this increased the tensile strength during the early aging stage. The PP matrix was entangled in the filler particles. Therefore, the filler particles were embedded in the matrix, and the fracture occurred in the PP matrix instead of at the interface between them. On the basis of these results, a “disappearing” filler mechanism for the PP composites was proposed. This work provides a possible way for improving the mechanical properties of PP composites with appropriate aging. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42546.     

Effect of filler surface treatment on mechanical properties and thermal properties of single and hybrid filler–filled PP composites

The influence of two types of surface treatments (aminosilane and Lica‐12) on the mechanical and thermal properties of polypropylene (PP) filled with single and hybrid filler (silica and mica) was studied. An improvement in tensile properties and impact strength was found for both treatments compared to those of untreated composites. However, the filler with silane coupling agent showed better improvement compared to the filler with Lica‐12 coupling agent. This was due to better adhesion between filler and matrix. Thermal analysis indicates that surface treatments increased the nucleating ability of filler, but decreased the coefficient of thermal expansion of PP composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polypropylene/silica micro‐ and nanocomposites modified with poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene)

The effects of different silica loadings and elastomeric content on interfacial properties, morphology and mechanical properties of polypropylene/silica 96/4 composites modified with 5, 10, 15, and 20 vol % of poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) SEBS added to total composite volume were investigated. Four silica fillers differing in size (nano‐ vs. micro‐) and in surface properties (untreated vs. treated) were chosen as fillers. Elastomer SEBS was added as impact modifier and compatibilizer at the same time. The morphology of ternary polymer composites revealed by light and scanning electron microscopies was compared with morphology predicted models based on interfacial properties. The results indicated that general morphology of composite systems was determined primarily by interfacial properties, whereas the spherulitic morphology of polypropylene matrix was a result of two competitive effects: nucleation effect of filler and solidification effect of elastomer. Tensile and impact strength properties were mainly influenced by combined competetive effects of stiff filler and tough SEBS elastomer. Spherulitic morphology of polypropylene matrix might affect some mechanical properties additionally. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41486.     

Improvement of the physico‐mechanical properties and stability of waste polypropylene in the presence of wood flour and (maleic anhydride)‐grafted polypropylene

This paper deals with (maleic anhydride)‐grafted polypropylene (MAH‐g‐PP) and wood flour reinforcement and their effects on the dynamic, mechanical, morphological, and rheological properties of waste polypropylene (PP) composites. MAH‐g‐PP was used as a compatibilizer to improve the physical interaction between the filler and matrix. The composites were prepared by using a twin‐screw extruder followed by injection molding. Thermal stability and mechanical properties of the compatibilized system increased as compared to their values for the uncompatibilized system. Also, nearly 60% and 30% loss was found for mechanical properties and weight loss, respectively, in a biodegradability study. J. VINYL ADDIT. TECHNOL., 20:24–30, 2014. © 2014 Society of Plastics Engineers     

Influence of stearic acid treatment of filler particles on the structure and properties of ternary‐phase polypropylene composites

In this study, ternary‐phase polypropylene (PP) composites containing an ethylene–octene copolymer (EOR) and calcium carbonate (CaCO₃) were investigated. Particular consideration was given to the influence of stearic acid treatment of the filler on the phase morphology and mechanical properties of the composites. In composites containing an uncoated filler, a separate dispersion of the elastomer and filler particles in the PP matrix was observed. The use of filler treated with stearic acid had no effect either on the dispersion or the interaction of the filler and the polymer components. However, the surface‐treated filler was found to promote the β‐hexagonal crystallization of PP and gave a composite with lower T_{c onset} and T_c values. As a consequence, differences in mechanical properties, in particular, impact strength, were exhibited in which calcium carbonate with stearic acid treatment was apparently more effective in increasing the impact strength of the composites in comparison with the composites containing the uncoated filler. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3445–3454, 1999     

Evaluation of dynamic elastic properties of wood‐filled polypropylene composites

Dynamic modulus of elasticity (MoE) and shear modulus of wood‐filled polypropylene composite at various filler contents ranging from 10% to 50% was determined from the vibration frequencies of disc‐shaped specimens. Wood filler was used in both fiber form (pulp) and powder form (wood flour). A novel compatibilizer, m‐isopropenyl‐α,α‐dimethylbenzyl‐isocyanate(m‐TMI) grafted polypropylene with isocyanate functional group was used to prepare the composites. A linear increase in dynamic MoE, shear modulus, and density of the composite was observed with the increasing filler content. Between the two fillers, wood fiber filled composites exhibited slightly better properties. At 50% filler loading, dynamic MoE of the wood fiber filled composite was 97% higher than that of unfilled polypropylene. Halpin‐Tsai model equation was used to describe the changes in the composite modulus with the increasing filler content. The continuous improvement in elastic properties of the composites with the increasing wood filler is attributed to the effective reinforcement of low‐modulus polypropylene matrix with the high‐modulus wood filler. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1706–1711, 2006     

Production and characterization of natural fiber‐reinforced thermoplastic composites using wheat straw modified with the fungus Pleurotus ostreatus

Wheat straw is an abundantly available and potentially valuable biomass that is currently under‐exploited. In this study, the feasibility of using wheat straw as a filler in high‐density polyethylene (HDPE)‐based composites was explored. Straw was treated with the white‐rot fungus Pleurotus ostreatus with the aim of improving adhesion between straw and plastic, and thereby the mechanical properties of the composite. Results indicate that the use of sterilized straw is necessary to inhibit the growth of indigenous organisms that preclude, likely through competition, removal of lignin, and hence, improved bonding between straw and plastic. Light and transmission electron microscopy revealed cell wall modification in sterilized, inoculated straw. Reduced thermal stability of treated straw did not negatively affect the production of injection‐molded straw–plastic composites (SPC). Comparable interfacial adhesion, based on activation energies obtained in dynamic mechanical analysis, was observed in untreated and treated straw‐ and pine‐based thermoplastic composites. The results of this study indicate that wheat straw represents a promising alternative to wood fillers in the production of thermoplastic composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5191–5201, 2006     

Upgrading brewer's spent grain as functional filler in polypropylene matrix

Brewer's spent grain (BSG) is a by‐product of the brewing industry that contributes to a large volume of wastes. The lignocellulosic nature of this waste, together with presence of functional components such as antioxidants, represents an attractive for the composite's industry. In this work, BSG has been used as functional filler for polypropylene matrix to give an additional use to this industrial waste. Addition of BSG filler improves the overall environmental efficiency of the polypropylene matrix thus leading to high environmentally friendly materials. BSG can be loaded in the 10–40 wt% range with easy manufacturing, balanced mechanical properties, and additionally, excellent antioxidant properties are achieved with increasing BSG loading due to natural antioxidants that have not been removed during the brewing process. In particular, the onset of the thermo‐oxidative degradation of polypropylene is improved by 15–20°C for different compositions. Due to the lignocellulosic nature of BSG, water uptake is a clear drawback of PP–BSG composites but formulations containing 10‐30 wt% BSG hold the water uptake at very low values. POLYM. COMPOS., 38:40–47, 2017. © 2015 Society of Plastics Engineers     

聚丙烯/麦秸秆木塑复合材料的力学性能

采用转矩流变仪混合造粒,通过注射成型方法制备了聚丙烯(PP)/麦秸秆木塑复合材料,研究了NaOH浓度、增容剂的含量和麦秸秆含量对PP/麦秸秆木塑复合材料力学性能的影响,采用扫描电子显微镜对麦秸秆表面及复合材料的断面形貌进行分析。结果表明:8%NaOH溶液处理麦秸秆时,PP/麦秸秆木塑复合材料的拉伸强度、弯曲强度和冲击强度达到最大;马来酸酐接枝PP增容剂的加入使得麦秸秆与PP的界面相容性提高,复合材料的力学性能增加;在一定范围内麦秸秆的添加降低了PP材料的拉伸强度和冲击强度,而提高了其弯曲强度,并且PP/麦秸秆复合材料的弯曲强度随着麦秸秆含量的增加而增加,在麦秸秆含量为30%时弯曲强度达到最大值为43.4 MPa。     

Effects of wheat straw fiber content and characteristics,and coupling agent concentration on the mechanical properties of wheat straw fiber‐polypropylene composites

Wheat straw fiber‐polypropylene (PP) composites were prepared to investigate the effects of wheat straw fiber content (10, 20, 30, 40, and 50 wt %), fiber size (9, 28, and 35 mesh), and maleic anhydride grafted polypropylene (MAPP) concentration (1, 2, 5, and 10 wt %) on the static and dynamic mechanical properties of the wheat straw fiber‐PP composites in this study. The tensile modulus and strength of the composites increased linearly with increasing wheat straw fiber content up to 40%, whereas the elongation at break decreased dramatically to 3.78%. Compared with the composites made of the longer wheat straw fiber, the composites made of the fines (>35 mesh) had a slightly higher tensile strength of 31.2 MPa and tensile elongation of 5.39% at break. With increasing MAPP concentration, the composites showed an increase in tensile strength, and the highest tensile strength of 34.0 MPa occurred when the MAPP concentration reached 10 wt %. As wheat straw fiber content increased from 0 to 40%, the flexural modulus of the composites increased gradually from 1335 to 3437 MPa. The MAPP concentration and wheat straw fiber size distribution had no appreciable effect on the static flexural modulus of the composites. The storage flexural modulus of the composites increased with increasing wheat straw fiber content. The scanning electron microscopy (SEM) observation on the fracture surface of the composites indicated that a high wheat straw fiber content (>30 wt %) resulted in fiber agglomeration and a reduction in interfacial bonding strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of functionalized polyolefin on interfacial adhesion of glass fiber‐reinforced polypropylene

Several types of functionalized polyolefins, grafted with maleic anhydride, were synthesized and used to modify the surface of fiberglass in reinforced polypropylene composites. The influence of maleated polyolefin, matrix, and compounding conditions on the interfacial bonding strength of composite were studied by measuring interfacial shear strength. The results showed that strong interactions, e.g., chemical bonding, were formed between maleated polyolefin and fiber surface. When the modified fibers were compounded with polypropylene, firm entanglements of molecular chain were formed due to the segmental interdiffusion between maleated polyolefin and matrix polypropylene. As a result, the degree of fiber‐matrix adhesion was improved. The extent of such improvement depended on the grafting degree, chain length of maleated polyolefin, and the compatibility between maleated polyolefin and matrix resin. At the same time, the compounding temperature and the cooling procedure affected the interfacial adhesion too. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1359–1365, 2000     

All‐straw‐fiber composites: Benzylated straw as matrix and additional straw fiber reinforced composites

With the aim to utilize the waste biomass of wheat straw, all‐straw‐fiber composites were elaborately manufactured though producing plastic benzylated wheat straw (BWS) as matrix and reinforced by additional straw fibers (ASF). The extent of benzylation for wheat straw was greatly improved with the aid of ball milling pretreatment for 4 h. BWS yielded higher weight percent gain (WPG) under the same reaction conditions with the benzylation of wood flour, lower glass transition temperature (T_g) as well as better flowability upon heating compared to benzylated mulberry branches (BMB) with comparable WPG. All‐straw‐fiber composites performed higher ASF loading capacity and better mechanical properties with optimum ASF content than BMB based composites and by benzylation decreased water absorption significantly. SEM provided evidence for strong adhesion in the interface between BWS and ASF. From the overall performance, the All‐straw‐fiber composites can be regarded as a potential alternative to wood plastic composites. POLYM. COMPOS., 35:419–426, 2014. © 2013 Society of Plastics Engineers     

Recycling of lignocellulosics filled polypropylene composites. I. Analysis of thermal properties,morphology, and amount of free radicals

Composites of isotactic polypropylene filled with comminuted rapeseed straw are studied. Improvement in interfacial adhesion is achieved by chemical modification of the lignocellulose filler. Composites were subjected to recycling by extrusion. The effect of multiple recycling of the composites on the process of nucleation and crystallization of polypropylene matrix, surface topography, and free radical generation was checked. On the basis of differential scanning calorimetry data, a significant influence of the recycling on nucleation activity of the lignocellulose filler was evidenced. A relation between the filler particle size and multiple recycling was established by observations under a polarization microscope, while scanning electron microscope analyses confirmed the positive effect of chemical modification of rapeseed straw on the interfacial adhesion. The composite structure changes forced by multiple recycling are discussed in the context of free radical generation. Concentration of free radicals in the rapeseed straw samples and composites was measured by the electron paramagnetic resonance spectroscopy to show that it was higher in the systems subjected to multiple recycling. Interestingly, the composites after multiple recycling showing elevated concentration of free radicals are also characterized by higher nucleation activity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41693.     

Monofunctional compatibilizer with long alkyl end for fabrication of superior tensile wood flour‐polyolefin composites

A novel monofunctional compatibilizer (OID) was prepared and used as compatibilizer for fabrication of wood‐plastic composites. OID was successfully synthesized by esterification reaction of isophorone diisocyanate and octadecanol as confirmed by Fourier transform‐infrared spectra. After OID modification, the hydrophobicity of wood flour surface was enhanced as indicated by the increase of surface water contact angle. By using OID as compatibilizer, an obvious enhancement of the interfacial adhesion between wood flour and polyolefin was observed by scanning electron microscopy. As a result, the tensile properties of the obtained polypropylene/wood flour composites and polyethylene/wood flour composites were significantly enhanced. Besides, the processability of polyolefin/wood flour composites was also improved by adding OID. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44429.     

High performance wood composites from highly filled polybenzoxazine

Highly filled systems prepared by compression molding of Hevea brasiliensis woodflour filled polybenzoxazine composites with high mechanical properties and reduced water uptake has been developed. The effects of percent filler content and particle size of woodflour on the obtained composite's properties were examined. The low melt viscosity of BA‐a type polybenzoxazine allows substantial amount of woodflour to be easily incorporated into the composites. The results showed that mechanical properties from dynamic mechanical analysis and flexural test at filler content below the optimum filler packing show approximately linear relationship with filler loading. The outstanding compatibility between the woodflour and the polybenzoxazine matrix is evidently seen from the large improvement in the composite's T_g and char yield. Scanning electron micrographs of the composite also reveals substantially strong interface between the woodflour filler and the polybenzoxazine matrix. Water absorption of the composites is greatly reduced with increasing the amount of polybenzoxazine due to the inherent low water absorption of the matrix. The polybenzoxazine is; therefore, a highly attractive candidate as high performance lignocellulosic binder or adhesive and other related applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1240–1253, 2006