Polypropylene Random Copolymer Matrix Research Articles

Investigation of tribo-mechanical performance of alkali treated rice-husk and polypropylene-random-copolymer based biocomposites

This study was based on the experimental performance evaluation of a wood polymer composite (WPC) that was synthesized by incorporating untreated and treated rice husk (RH) fibers into a polypropylene random copolymer matrix. The submicron-scale RH fibers were alkali-treated to modify the surface and introduce new functional groups in the WPC. A compatibilizer (maleic anhydride) and a thermos-mechanical properties modifier (polypropylene grafted with 30 % glass fiber) were used in the WPC. The effects of untreated and treated RH on the WPC panels were studied using FESEM, FTIR, and microscope images. A pin-on-disk setup was used to investigate the bulk tribological properties of PPRC and WPC. The complex relationship between the friction coefficient of different loading of RH fibers in the WPC, as a function of sliding distance, was analyzed along with the temperature and morphology of the surface. It was observed that untreated RH acted as a friction modifier, while treated RH acted as a solid lubricant. Microhardness was calculated using the QCSM module on nanoindentation. It was found that untreated RH led to an increase in microhardness, while treated RH caused a decrease in hardness compared to PPRC.

Multifunctional characteristics of 3D printed polymer nanocomposites under monotonic and cyclic compression

This study presents the multifunctional characteristics of multi-walled carbon nanotube (MWCNT)/polypropylene random copolymer (PPR) composites enabled via fused filament fabrication (FFF) under monotonic and quasi-static cyclic compression. Utilizing in-house MWCNT-engineered PPR filament feedstocks, both bulk and cellular composites were realized. The morphological features of nanocomposites were examined via scanning electron microscopy, which reveals that MWCNTs are uniformly dispersed. The uniformly dispersed MWCNTs forms an electrically conductive network within the PPR matrix, and the resulting nanocomposite shows good electrical conductivity (⁓10−1S/cm), improved mechanical performance (modulus increases by 125% and compressive strength increases by 25% for 8 wt% MWCNT loading) and pronounced piezoresistive response (gauge factor of 27.9–8.5 for bulk samples) under compression. The influence of strain rate on the piezoresistive response of bulk samples (4 wt% of MWCNT) under compression was also measured. Under repeated cyclic compression (2% constant strain amplitude), the nanocomposite exhibited stable piezoresistive performance up to 100 cycles. The piezoresistive response under repeated cyclic loading with increasing strain amplitude of was also assessed. The gauge factor of BCC and FCC cellular composites (4 wt% of MWCNT) with a relative density of 30% was observed to be 46.4 and 30.2 respectively, under compression. The higher sensitivity of the BCC plate-lattice could be attributed to its higher degree of stretching-dominated deformation behavior than the FCC plate-lattice, which exhibits bending-dominated behavior. The 3D printed cellular PPR/MWCNT composites structures were found to show excellent piezoresistive self-sensing characteristics and open new avenues for in situ structural health monitoring in various applications.

Thermomechanical Characterization of E‐Glass Fiber Reinforced Random Polypropylene

AbstractThe thermomechanical properties of short glass fiber (GF) reinforced polypropylene random copolymer (PPR) composites are investigated. Four composites with different fiber content, namely 10, 15, 20, and 30 wt%, are prepared using melting mixing. For fibers up to 15 wt% the composites exhibit enhanced thermal stability as compared to the random polypropylene. The use of fibers also improve the mechanical strength of the matrix. In particular, PPR/GF30% demonstrates the highest Young modulus, yield strength, and storage modulus values, while PPR/GF10% has the best ductility among the composites. Incorporation of 10 wt% fibers also increases the yield strength and storage modulus of the PPR matrix by approximately 1.6 and 1.2 (for temperatures higher than 60°C) times, respectively. These results suggest that GF reinforced PPR is a composite suitable for advanced technological applications.

Adjustable brittle-ductile transition behavior and rheological behavior of polypropylene random copolymer nanocomposites through well interfacial-loaded nanoparticles

To improve the low-temperature toughness of polypropylene random copolymer (PPR), a series of PPR/ethylene-propylene rubber/silica (PPR/EPR/SiO2) nanocomposites were prepared through toughening strategy based on interfacial-loaded particles and adjustable dispersed phase. The results showed that the brittle-ductile transition behavior for PPR/EPR/SiO2 nanocomposites could be adjusted by silica and rubber contents, and consequently the composites were endowed with excellent low-temperature impact resistance. Furthermore, the nanocomposites never presented the significant deterioration of rigidity compared with pure PPR. The dynamic rheological results showed that viscosity change in PPR matrix and EPR phase could make silica particles preferentially locate at PPR-EPR interface, which strongly reduced the size of EPR domain and consequently led to a stronger shape relaxation of long-time scale. According to dynamic rheological behavior, microstructure and interparticle distance analysis of PPR nanocomposites, the adjustable brittle-ductile transition behavior was ascribed to the reduced rubber interparticle distance coming from the well interfacial-loaded nanoparticles.

Composites of a Polypropylene Random Copolymer and Date Stone Flour: Crystalline Details and Mechanical Response.

Several composites were prepared based on a polypropylene random copolymer (PPR) and different amounts of date stone flour (DSF). This cellulosic fiber was silanized beforehand in order to reduce its hydrophilicity and improve the interfacial adhesion with the polymer. Other composites were also obtained, including a sorbitol derivative as an effective nucleant. Films made from these composites were prepared using two different thermal treatments, involving slow crystallization and rapid cooling from the melt. Scanning electron microscopy was used to evaluate the morphological features and the DSF particle dispersion within the PPR matrix. X-ray diffraction experiments and differential scanning calorimetry tests were employed to assess the crystalline characteristics and for the phase transitions, paying especial attention to the effects of the DSF and nucleating agent on PPR crystallization. An important nucleation ability was found for DSF, and evidently for the sorbitol derivative. The peak crystallization temperature upon cooling was considerably increased by the incorporation of either the nucleant or DSF. Additionally, a much higher proportion of orthorhombic crystals developed in relation to the monoclinic ones. Moreover, the mechanical responses were estimated from the microhardness experiments and significant improvements were found with increasing DSF contents. All of these findings indicate that the use of silanized DSF is a fairly good approach for the preparation of polymeric eco-composites, taking advantage of the widespread availability of this lignocellulosic material, which is otherwise wasted.

Electromagnetic interference shielding performance of carbon nanostructure reinforced, 3D printed polymer composites

We report the electrical, mechanical and electromagnetic interference (EMI) shielding performance of polypropylene random copolymer (PPR)/multi-wall carbon nanotube (MWCNT) nanocomposites enabled via customized fused filament fabrication process. The electro-conductive PPR/MWCNT filament feedstocks were fabricated via shear-induced melt-blending process that allows 3D printing of nanoengineered composites even at higher MWCNT loading (up to 8 wt%). The uniform dispersion of MWCNTs in PPR matrix confirmed via Raman spectroscopy and scanning electron microscopy facilitates better mechanical, electrical and EMI shielding performance. The results furthermore show enhanced shielding properties and higher attenuation for the nanocomposites printed in 90° direction (~ − 37 dB for 8 wt% MWCNT loading). Effective interfacial adhesion between the beads with lesser extent of voids (confirmed via micro-computed tomography) endorsed low transmission loss in nanocomposites printed in 90° direction compared to samples printed in 0° direction. Surface architected structure (frustum shape) reveals higher specific shielding effectiveness (maximum ~ − 40 dBg−1cm3, + 38%) over the plain structure. The realization of excellent shielding effectiveness (~ 99.9% attenuation) of additive manufacturing-enabled PPR/MWCNT nanocomposites demonstrates their potential for lightweight and strong EMI shields.Graphical

Impact behavior of nanoengineered, 3D printed plate-lattices

Herein, we investigate the low-velocity impact behavior of polypropylene random copolymer (PPR)/multi-wall carbon nanotube (MWCNT) and high-density polyethylene (HDPE)/MWCNT plate-lattices processed via fused filament fabrication additive manufacturing, utilizing in-house nanoengineered filament feedstocks. We examine the dynamic crushing and energy absorption characteristics of three typical elementary plate-lattices, namely, simple cubic (SC), body-centered cubic (BCC) and face-centered cubic (FCC) as well as three hybrid plate-lattices (SC-BCC, SC-FCC and SC-BCC-FCC) comprising different weight fractions of MWCNTs at different impact energy levels. The results reveal that the SC-BCC-FCC nanocomposite plate-lattice offers the most favorable impact response as each constituent plate in the lattice contributes to the load carrying capacity for all direction vectors included in the plane of the plate. Furthermore, the results show that impregnating MWCNTs into the PPR and HDPE plate-lattices significantly influences their impact energy attenuation characteristics. Compared with the respective unreinforced plate-lattices, PPR/6 wt% MWCNT SC-BCC-FCC plate-lattices evince higher energy absorption (70%) than HDPE/6 wt% MWCNT SC-BCC-FCC plate-lattices (47%) due to uniform MWCNT dispersion and effective interfacial interaction of MWCNTs in PPR matrix. Our hybrid 3D plate-lattices exhibit a specific energy absorption (SEA) capacity as high as 19.9 J/g, demonstrating their superior impact performance over aluminum and other conventional lattices.

Thermo-resistive and thermo-piezoresistive sensitivity of carbon nanostructure engineered thermoplastic composites processed via additive manufacturing

We experimentally examine the thermo-resistive and thermo-piezoresistive sensitivity of multiwall carbon nanotube (MWCNT)/polypropylene random copolymer (PPR) nanocomposites processed via fused filament fabrication (FFF) process. The filament feedstocks were fabricated by melt blending of neat PPR with a predetermined amount of MWCNTs (either 4, 6 or 8 wt%) using a twin-screw extruder. Thermo-resistive characteristics of MWCNT/PPR composites were measured under both constrained and unconstrained heating from approximately 30-100 °C. For all MWCNT concentrations considered here, negative temperature coefficients of resistivity (TCR) were observed for both constrained and unconstrained heating, as a consequence of thermal fluctuation-induced tunneling at MWCNT junctions. The highest thermo-resistive sensitivity was measured for the composite with the lowest MWCNT concentration (4 wt%) under unconstrained conditions, reporting a TCR of −12,800 × 10−6/°C, which is higher in magnitude than that of other polymer nanocomposites reported in the literature. Moreover, the MWCNT/PPR composites exhibit strong thermo-piezoresistive response under tensile loading. For 4 wt% MWCNT loading, the gauge factor (measured over 0–20% strain range) of the composite increased from 27.8 to 52.3 when the temperature was raised from 30 °C to 60 °C. Our results further evince higher thermo-piezoresistive sensitivity i.e., a gauge factor as high as 395 at 60 °C. The electron tunneling and hopping, both thermally-assisted and activated by mechanical deformation of the PPR matrix, significantly increase the thermo-piezoresistance with the increase in temperature in this range. The excellent thermo-resistive and thermo-piezoresistive characteristics of MWCNT/PPR composites reported in this study would enable the development of smart nanocomposites for self-sensing both temperature and strain/damage state.

Synergetic Toughening Effect of Carbon Nanotubes and β-Nucleating Agents on the Polypropylene Random Copolymer/Styrene-Ethylene-Butylene- Styrene Block Copolymer Blends.

Polypropylene random co-polymer (PPR)/styrene-ethylene-butylene-styrene (SBS) block copolymer blends with high toughness and favorable tensile properties were successfully obtained by blending with traces of multi-wall carbon nanotubes (MWCNTs) and β-nucleating agents (β-NAs). β-NAs can effectively induce the ductile β-form crystal in the PPR matrix. Although the addition of MWCNTs was reported to be only benefit for the tensile strength of PPR and relatively disadvantageous for the toughness, the obviously synergistic toughening effect in PPR/SBS blends was found when MWCNTs and β-NAs coexisted. The notched izod impact strength of PPR/30 wt % SBS blend with MWCNTs and β-NAs increased from 11.3 to 58.9 kJ/m2; more than 5-fold increment compared with pure PPR. Meanwhile, the tensile strength retention of this PPR blend is still above 72.2%. The micro-morphology indicated that the MWCNTs can act as bridges between SBS particle and PPR matrix, effectively transferring the stress and absorbing impact energy among SBS particles.

Synergistic Toughening Effect of Olefin Block Copolymer and Highly Effective β-Nucleating Agent on the Low-Temperature Toughness of Polypropylene Random Copolymer

In the present work, the synergistic toughening effect of olefin block copolymer (OBC) and a highly effective β nucleating agent (NA)-Calcium salt of pimelic acid (CaPim) on polypropylene random copolymer (PPR) was studied. Mechanical tests showed that with the introduction of 0.1 wt % CaPim, there was almost no change in the low-temperature (below 0 °C) toughness of PPR. Although introduction of OBC could obviously improve the toughness at 23 °C, high content is needed to effectively toughen PPR at low temperature. By coadding OBC and CaPim, PPR/OBC/NA blends showed not only great enhancement of toughness over the temperature range tested but also lower OBC content of undergoing brittle-ductile transition compared with PPR/OBC blends. The crystalline structure, crystallization behavior and phase morphology were investigated to explore the possible synergistic toughening mechanism. The high β-crystal content formed in PPR matrix and the finer distribution of OBC phase might be responsible for the superior...

Toughened polypropylene random copolymer with olefin block copolymer

In this work, the toughening effect of olefin block copolymer (OBC) on polypropylene random copolymer (PPR) at room and low temperature (0°C) was investigated. Mechanical tests showed that OBC is an effective impact modifier for PPR. By addition of only 5wt% of OBC, the notched Izod impact strength of resulting blends at room temperature and 0°C are 66.5, 9.27kJ/m2, which are increased 135.8 and 43.9%, respectively. This value for blends containing 10wt% OBC at 0°C is 60.2kJ/m2, which is approximately eight times higher than that of pristine PPR at same temperature. Due to the high melting point of OBC, the decline of rigidity caused by its addition is rather slight. The tensile strength and flexural modulus for blends containing 10wt% OBC is only 8.3 and 11.3% lower than that of pristine PPR. The investigation of morphology, crystallization and rheological behaviors suggested that the great improvement of toughness might be attributed to the decrease of PPR spherulites size and the excellent compatibility between PPR matrix and OBC dispersed phase. This work offers a simple and effective approach to produce PPR with stiffness–toughness balance.

Dynamic mechanical properties, crystallization behaviors, and low‐temperature performance of polypropylene random copolymer composites

ABSTRACTIn this study, polypropylene random copolymer (PPR) composites were prepared by the addition of either three kinds of thermoplastic rubber (TPR) modifiers (types 2088A, 2095, and 2096) or an ethylene–octene copolymer (POE)/high‐density polyethylene (HDPE; 2 :1 w/w) blend. Differential scanning calorimetry, wide‐angle X‐ray diffraction, and dynamic mechanical analysis were used to characterize the crystallization behaviors and dynamic mechanical properties of the PPR composites. The results indicated that PPR/POE/HDPE and PPR/TPR2088A had better comprehensive mechanical properties, especially the low‐temperature toughness among all of the samples. The obtained PPR/POE/HDPE blends showed a high toughness and good stiffness in the temperature interval from −10 to 23°C with the addition of only 10 wt % POE/HDPE. When the temperature continued to fall below −10°C, the PPR/TPR2088A composites exhibited a better impact toughness without a loss of too much stiffness. The good low‐temperature toughness of those two composites was attributed to both the decrease in the crystallinity and the uniform dispersion, obvious interfacial adhesion, and cavitation ability of POE/HDPE and TPR2088A in the PPR matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42960.

Excellent electromagnetic interference shielding and mechanical properties of high loading carbon-nanotubes/polymer composites designed using melt recirculation equipped twin-screw extruder

This paper describes for the first time a facile, scalable and commercially viable melt blending approach involving use of twin-screw extruder with melt recirculation provision, for uniform dispersion of up to 4.6vol% multiwall carbon nanotubes (MWCNTs) within polypropylene random copolymer (PPCP). Morphological characterization of PPCP/MWCNT nanoscale composites (NCs) was done using scanning electron microscopy and transmission electron microscopy, which show good dispersion of MWCNTs in the PPCP matrix even at high loadings and confirm the formation of true NCs. The improved dispersion leads to the formation of electrically conducting three dimensional networks of MWCNTs within PPCP matrix at very low percolation threshold (∼0.19vol%). The attainment of dc conductivity value of ∼10−3S/cm, tensile strength of ∼42MPa and good thermal stability for 4.6vol% MWCNTs loading NC along with electromagnetic interference (EMI) shielding effectiveness (SE) value of −47dB (>99.99% attenuation), demonstrate its potential for making light weight, mechanically strong and thermally stable EMI shields. These NCs also display specific SE value of ∼−51dBcm3/g which is highest among unfoamed polymer NCs.

Effect of nano-ZnO-supported 13X zeolite on photo-oxidation degradation and antimicrobial properties of polypropylene random copolymer

To improve the photo-oxidation degradation resistance and antimicrobial ability of ZnO-filled polypropylene random copolymer (PPR), 13X zeolite particles supported with nano-ZnO with different morphologies were prepared and used to manufacture filled PPR composites. The formation of ZnO with different morphologies on the surface of 13X zeolite was proved by atomic absorption spectroscopy, scanning electron microscope, UV–vis spectra, and fluorescence spectra. The results indicated that the photo-oxidation degradation resistance of nano-ZnO-supported 13X zeolite-filled PPR composites is higher than that of PPR composites filled by the same content of pure nano-ZnO. Antimicrobial experiment results show that nano-ZnO-supported 13X zeolite-filled PPR composites exhibit higher antimicrobial properties than ZnO-filled PPR composites prepared by directly adding nano-ZnO into PPR matrix for Staphylococcus aureus and Escherichia coli. The addition of nano-ZnO-supported 13X zeolite particles increases the crystallization temperature, but has no influence on the melting behavior of PPR composites.

Coeffect of different core–shell particles and β nucleating agent on the mechanical and thermal properties of polypropylene random copolymer composites

The coeffect of β-nucleating agent (β-NA) and different core–shell particles (CSPs) on improving the mechanical properties and thermal stability of polypropylene random copolymer (PPR) composites were investigated. Different CSPs, that is, the regular POE/nano-calcium carbonate (CaCO3) and the novel PE/nano-CaCO3 CSP were prepared through melt blending. The transmission electron microscopic micrograph demonstrated that the core–shell structure was successfully prepared and the CSP dispersed homogeneously in the PPR matrix. β-NA was also introduced into the PPR matrix to control the crystalline structure. The results of differential scanning calorimetry, wide-angle x-ray diffraction, and polarization optical microscopy showed that the relative content of β-form crystal was greatly enhanced in the presence of β-NA. The results of the mechanical tests and thermal gravimetric analysis indicated that the comprehensive mechanical properties and thermal stability were all greatly improved, especially for the sample with the incorporation of both β-NA and PE/nano-CaCO3 CSP.

Preparation, antimicrobial, crystallization and mechanical properties of nano-ZnO-supported zeolite filled polypropylene random copolymer composites

In order to increase the antimicrobial functionality of polypropylene random copolymer (PPR), nano-ZnO-supported on the surface of zeolite particles were prepared and used as functional fillers for PPR composites. The prepared nano-ZnO-supported zeolite particles were characterized by fluorescence and UV–Vis spectra, inductive coupled plasma and scanning electron microscopy. The crystallization behavior and crystalline morphology, antimicrobial ability and mechanical properties of zeolite, ZnO and nano-ZnO-supported zeolite filled PPR composites were investigated by differential scanning calorimeter, polarizing optical microscopy, antimicrobial and mechanical testing. The results indicated that the ZnO with flower-like morphology was formed on the surface of zeolite particles. The heterogeneous nucleation of zeolite and nano-ZnO-supported zeolite increase the crystallization temperature of PPR. The crystallization temperatures of nano-ZnO-supported zeolite filled PPR composites increase with increasing ZnO content in the nano-ZnO-supported zeolite. Incorporation of nano-ZnO-supported zeolite significantly decreases the size of spherulites of PPR. The nano-ZnO-supported zeolite filled PPR composites exhibit higher antimicrobial abilities than nano-ZnO filled PPR composite prepared by directly adding the same content of nano-ZnO into PPR matrix for the Staphylococcus aureus and Escherichia coli due to the flower-like morphology of ZnO in the nano-ZnO-supported zeolite. The nano-ZnO-supported zeolite content has little influence on the mechanical properties of PPR composites. nano-ZnO-supported zeolite as functional filler can be used to increase the antimicrobial ability of PPR.

Synergistic effects of β‐modification and impact polypropylene copolymer on brittle‐ductile transition of polypropylene random copolymer

AbstractIn this work, the synergistic effects of β‐modification and impact polypropylene copolymer (IPC) on brittle–ductile (B–D) transition behavior of polypropylene random copolymer (PPR) have been investigated. It is interesting to find that adding both IPC and β‐nucleating agent into PPR has three effects: (i) leading to a significant enhancement in β‐crystallization capability of PPR, (ii) contributing to the shift of B–D transition to lower temperatures, (iii) increasing the B–D transition rate. The reason for these changes can be interpreted from the following two aspects. On one hand, the transition of crystalline structure from α‐form to β‐form reduces the plastic resistance of PPR matrix, thus causing the initiation of matrix shear yielding much easier during the impact process. On the other hand, the well dispersed rubbery phase in IPC with high molecular mobility at relatively low temperatures is beneficial to the shear yielding of PPR matrix and, subsequently, the great improvement in impact toughness of the ternary blends. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Synergistic toughening of polypropylene random copolymer at low temperature: β-Modification and annealing

Abstract The synergistic effect of β-modification and annealing on the impact toughness of a commercially available polypropylene random copolymer (PPR) was investigated. Interestingly, the impact toughness of β-nucleated PPR after annealing at low temperature (0 °C) was almost five times as high as that of the virgin PPR without annealing. The crystalline structure, supermolecular structure, phase morphology, the relaxation of chain segments and fracture behavior of matrix were investigated to explore the toughening mechanism related to the β-modification and annealing. It was found that annealing improved the mobility of chain segments in amorphous phase as well as the strength of ligament of PPR matrix with profuse β crystals having the intrinsic low plastic deformation resistance, responsible for the superior toughness achieved. This work provides a possible method to toughen semi-crystalline polymers at low temperature by combination of β-modification and suitable annealing.

Super-toughed polymer blends derived from polypropylene random copolymer and ethylene/styrene interpolymer

In this article, blends of polypropylene random copolymer (PP-R) with a novel impact modifier, namely ethylene/styrene interpolymer (ESI), were prepared to evaluate the effectiveness of ESI in toughening PP-R and the influence of ESI content on the mechanical, thermal, and rheological properties of polymer blends. Results showed that super-toughened PP-R/ESI blends (ca. Izod impact strength ≥ 500 J/m) were readily achieved with only 5 wt % ESI. The blends exhibited significant improvement in both impact strength and elongation, while small loss in tensile strength and elastic modulus when increasing ESI content. ESI had a nucleating effect that caused PP matrix to crystallize at higher temperatures, whereas PP-R/ESI blends presented lower melting temperatures (T m ) than PP-R matrix and T m decreased with the increment of ESI content. Rheology study indicated that both PP-R matrix and PP-R/ESI blends presented shear thinning behaviors during melt processing.

Hierarchy crystallization structure of a polypropylene random copolymer injection‐molded bar induced by a nucleating agent

AbstractIn this work, the effect of a nucleating agent on the crystallization structure of an injection‐molded bar of a polypropylene random copolymer (PPR) with sorbitol derivatives [1,2,3,4‐dibenzylidene sorbitol (DBS)] has been studied. The results show that pure PPR forms a simple skin–core crystallization structure. However, PPR/DBS forms an interesting and complicated hierarchy crystallization structure: there is a transition layer between the skin layer and the core zone. In this transition layer, the crystallization structure consists of some perfect spherulites and many tiny crystallites. Further research suggests that the formation of the hierarchy crystallization structure depends on not only the content of the nucleating agent in the PPR matrix but also the mold temperature during the injection‐molding processing. The crystallization behavior of PPR/DBS during the cooling process has been characterized with polarization optical microscopy and differential scanning calorimetry. The results suggest that there are different mechanisms in the crystallization process of PPR/DBS. The formation of a three‐dimensional DBS network under a certain condition might be the main reason for the complicated hierarchy crystallization structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008