Thermal conductivity of polypropylene composites with hybrid fillers of boron nitride and vapor‐grown carbon fiber

High thermal conductivity fillers of boron nitride (BN) and vapor‐grown carbon fiber (VGCF) were used alone or incorporate to prepare polypropylene (PP) composites. The effects of filler content, particle size and shape, and single vs. hybrid BN/VGCF fillers were investigated with respect to the thermal conductivity of the PP composites. The thermal conductivity of PP/BN composites depended upon the content and particle size of the BN. Increased content and length of VGCF had the effect of increasing the thermal conductivity of the PP composites. Hybrid fillers were created with a mixture of medium‐sized BN and long‐length VGCF; hybrid BN/VGCF fillers enhanced the thermal conductivity of PP composites with a lower total content compared with PP composites containing only medium‐sized BN particles. POLYM. COMPOS., 37:936–942, 2016. © 2014 Society of Plastics Engineers     

Low dielectric and high thermal conductivity epoxy nanocomposites filled with NH2‐POSS/n‐BN hybrid fillers

Hybrid fillers of mono‐amine polyhedral oligomeric silsesquioxane/nanosized boron nitride (NH₂‐POSS/n‐BN) were performed to fabricate NH₂‐POSS/n‐BN/epoxy nanocomposites. Results revealed that the dielectric constant and dielectric loss values were decreased with the increasing addition of NH₂‐POSS obviously, but increased with the increasing addition of BN fillers. For a given loading of NH₂‐POSS (5 wt %), the thermal conductivities of NH₂‐POSS/n‐BN/epoxy nanocomposites were improved with the increasing addition of n‐BN fillers, and the thermal conductivity of the nanocomposites was 1.28 W/mK with 20 wt % n‐BN fillers. Meantime, the thermal stability of the NH₂‐POSS/n‐BN/epoxy nanocomposites was also increased with the increasing addition of n‐BN fillers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41951.     

BN填充PA6基导热绝缘复合材料导热性能研究

以聚酰胺6（PA6）为基体, 氮化硼（BN）作为导热填料,经双螺杆挤出机熔融共混,模压成型制得导热绝缘复合材料。研究了BN含量、粒径、形状和不同BN粒径复配对复合材料导热性能的影响,并研究了BN含量和粒径对复合材料绝缘性能的影响。结果表明,在各种粒径下,复合材料热导率均随BN填充量的增加而增大;在BN粒径为5 μm、填充量为25 %（体积分数,下同）时,复合材料热导率达到1.2187 W/(m·K);在BN填充量相同时,填料粒径对复合材料热导率的影响不是简单的单调规律,呈现50、100 μm时较小,1、5、15 μm时较大,150 μm时最大的规律;片状BN填料比球状BN填料更有利于提高复合材料的热导率;2种不同粒径填料复配所填充的复合材料的热导率大于单一粒径填充的复合材料;5 μm与150 μm粒径BN复配,在填充量为20 %,配比为1:3时,复合材料的热导率最大,达到1.3753 W/(m·K),为纯PA6的4.9倍;在不同BN含量和粒径下,复合材料体积电阻率均能达到10000000000000 Ω·cm以上,满足绝缘性能。     

Effect of filler size distribution on the mechanical and physical properties of alumina‐filled silicone rubber

The properties of silicone rubber filled with three kinds of binary mixtures of alumina particles with different size distribution (i.e., 30 μm + 0.5 μm, 10 μm + 0.5 μm, and 5 μm + 0.5 μm) were investigated as a function of relative volume fraction of the 0.5 μm particles in the hybrid alumina (V_s) at a fixed total filler content of 55 vol%. The results indicate that each binary mixture of alumina‐filled silicone rubber exhibited improved thermal conductivity and tensile strength, and decreased dielectric constant, compared to a single particle size filler‐reinforced one, and the maximum improvements were obtained at the V_s ranging from 0.2 to 0.35; the coefficient of thermal expansion (CTE) of filled silicone rubber obviously reduced with increase in the V_s, whereas the elongation at break slightly decreased. At V_s = 0, the larger particles‐filled silicone rubber showed higher thermal conductivity, CTE, dielectric constant, and elongation at break, and lower tensile strength compared with the those of the smaller particles‐filled one. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Rheology of low‐density polyethylene + Boehmite composites

Polyethylene is already one of the most commonly used polymers due to its solvent resistance and easy processing. Low‐density polyethylene (LDPE) also has excellent flexibility and resilience. However, the mechanical properties of LDPE are often poor. We added the inexpensive ceramic filler Boehmite to LDPE, simultaneously improving mechanical properties and reducing production cost—as Boehmite is cheap and abundant while the filler reduces the amount of petroleum‐derived polymer per unit weights of product. Additionally, less environmental contamination results at the end of service life since the Boehmite need not undergo degradation as the LDPE does. To aid adhesion between the matrix and filler, we introduced silane coupling agents (SCAs) to bond the hydrophobic LDPE to the hydrophilic Boehmite. Furthermore, since fillers ordinarily increase viscosity, it was essential to maintain a low viscosity for easy processability. We evaluated by rheometry the effect of the Boehmite on the melt viscosity of the LDPE + Boehmite composites and determined that the addition of any type of Boehmite decreases the viscosity compared to that of neat LDPE. The effects were explained by fiber formation and enhanced rigidity while the allowance for a lower processing temperature results in further energy and therefore cost savings. We also show that high‐temperature exposure of Boehmite during any part of the sample processing results in a decrease in the coupling efficiency of the matrix to filler and in a higher melt viscosity; yet the viscosity is still lower than for neat LDPE. POLYM. COMPOS., 31:1909–1913, 2010. © 2010 Society of Plastics Engineers.     

Effect of orientation and content of carbon based fillers on thermal conductivity of ethylene‐propylene‐diene/filler composites

In this study, synthetic graphite, carbon fiber, and carbon nanotube were used as thermal conductive fillers and ethylene‐propylene‐diene (EPDM) as matrix. Oriented EPDM/filler composites were prepared with two‐roll mill, and the effects of orientation and content of carbon based fillers on thermal conductivity and tensile strength of the composites were investigated. Parallel thermal conductivity of the oriented composites is significantly higher than normal thermal conductivity of the oriented composites. Especially, at 31.6% graphite content, parallel thermal conductivity of oriented composites is 7.14 W/mK. Very high thermal conductivity was achieved for oriented EPDM/graphite composites. Orientation of the fillers using two‐roll mill significantly improves the thermal conductivity in the orientation direction. For all the EPDM/filler composites, tensile strength of orientation direction is higher than that of normal direction. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41000.     

The influence of the dispersed phase on the morphology,mechanical and thermal properties of PLA/PE‐LD and PLA/PE‐HD polymer blends and their nanocomposites with TiO2 and CaCO3

This research investigated the impact of different processing temperature (extrusion at 160°C and 180°C) and the influence of the TiO₂ and CaCO₃ fillers on morphology, mechanical, and thermal properties of polylactide (PLA) blended with low‐density polyethylene (PE‐LD) and high‐density polyethylene (PE‐HD) in 90/10 weight ratio. The impact of the particle size of the filler was also examined with the three types of TiO₂ filler. It has been shown that the different processing temperature has no significant impact on the morphology, mechanical, and thermal properties of PLA/PE‐LD 90/10 and PLA/PE‐HD 90/10 polymer blends. It has also been shown that better phase interaction is not the crucial factor for the improvement of the mechanical properties but the domain size distribution of the dispersed phase within the matrix and the dispersion of the filler are. Samples with a narrow size distribution of the dispersed phase domain (5 to 10 μm) with the higher portion of larger domains that are uniformly distributed within the polymer matrix showed best mechanical properties. POLYM. ENG. SCI., 59:1395–1408 2019. © 2019 Society of Plastics Engineers     

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     

Experimental study of sharp‐tipped projectile perforation of GFRP plates containing sand filler under high velocity impact and quasi‐static loadings

Penetration and perforation behavior of glass fiber reinforced plastic (GFRP) plates containing 20% sand filler have been investigated via high velocity impact tests using sharp tipped (30°) projectile and quasi‐static perforation tests. Two size sand filler (75 and 600 μm) were used in 4‐, 8‐, and 14‐layered laminated composite plates to study sensitivity of filler size toward loading system. Composite plates were examined for perforation load rate at 5 mm/min and high‐velocity impact loading up to 220 m/s. Results indicated higher energy absorption for GFRP plates containing sand filler for both high‐velocity impact and quasi‐static perforation tests. Higher ballistic limits were recorded for specimens containing sand filler. The study showed clear role played by coarse‐sized sand filler as a secondary reinforcement in terms of higher energy absorption as compared with nonfilled and specimens containing fine‐sized fillers. The investigation successfully characterized behavior of quasi‐static test during penetration and perforation of the sharp‐tipped indenter as an aid for impact application studies. Residual frictional load in the specimens containing sand filler constituted considerable portion of load bearing during perforation in quasi‐static tests. Delaminations followed by fiber and matrix fracture were major failure mode in high‐velocity tests and the main energy absorbing mechanism in thick‐walled plates, whereas in quasi‐static tests the failures were more of matrix fracture and fiber sliding. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Electrical conductivity and EMI shielding effectiveness of polyurethane foam–conductive filler composites

The morphological, electrical, and thermal properties of polyurethane foam (PUF)/single conductive filler composites and PUF/hybrid conductive filler composites were investigated. For the PUF/single conductive filler composites, the PUF/nickel‐coated carbon fiber (NCCF) composite showed higher electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) than did the PUF/multiwall carbon nanotube (MWCNT) and PUF/graphite composites; therefore, NCCF is the most effective filler among those tested in this study. For the PUF/hybrid conductive fillers PUF/NCCF (3.0 php)/MWCNT (3.0 php) composites, the values of electrical conductivity and EMI SE were determined to be 0.171 S/cm and 24.7 dB (decibel), respectively, which were the highest among the fillers investigated in this study. NCCF and MWCNT were the most effective primary and secondary fillers, and they had a synergistic effect on the electrical conductivity and EMI SE of the PUF/NCCF/MWCNT composites. From the results of thermal conductivity and cell size of the PUF/conductive filler composites, it is suggested that a reduction in cell size lowers the thermal conductivity of the PUF/conductive filler composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44373.     

Highly thermally conductive room‐temperature‐vulcanized silicone rubber and silicone grease

In this study, the effects of thermally conductive filler type (α‐Al₂O₃, SiC), volume fraction of the filler, and filler particle size distribution on the thermal conductivity and viscosity of room‐temperature‐vulcanized (RTV) silicone rubber and silicone grease were investigated. We were interested to find that silicone grease (or the RTV silicone rubber) had a maximum thermal conductivity (～1.48 W/mK) and a minimum viscosity (～3.4 × 10⁴ mPa s), with a definite total volume fraction of the filler (0.55) when the distribution of filler sizes (the number ratio of two different particles sizes, i.e., 0.8 and 6 μm) was 600–700. We were able to increase the thermal conductivity of the RTV silicone rubber and silicone grease beyond 2 W/mK by increasing the total volume fraction of the filler with adequate filler size distributions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2397–2399, 2003     

Preparation of polydimethylsiloxane‐coated α‐alumina fillers with cold plasma for elastomer thermal interface materials

A novel method for the organic modification of a ceramic thermal conductive filler (α‐alumina) with cold plasma was developed for the preparation of elastomer thermal interface materials with high thermal conductivities and low moduli. The α‐alumina fillers were first coated with low‐molecular‐weight polydimethylsiloxane (PDMS) by solution dispersion and then treated in argon plasma for different time. The modified α‐alumina fillers were characterized with high‐resolution transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy. The results revealed that a thin PDMS film with several nanometers thick was tightly coated on the surface of the alumina filler after plasma treatment, and this thin film could not be removed by 48 h of Soxhlet extraction with n‐hexane at 120°C. Plasma modification of the alumina could dramatically weaken the strength of the filler–filler networks and, thus, remarkably reduce the modulus of the alumina‐filled silicone rubber composites but did not affect the thermal conductivity of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of soybean‐oil‐based polyurethane composites containing industrial and agricultural residual wastes as fillers

Thermosetting composites were prepared from soybean‐oil‐based polyols (hydroxyl number = 190 mg of KOH/g, [OH]/[NCO] for 2,4‐toluene diisocyanate = 0.9) and fillers (10 wt %) from industrial and agricultural residual wastes. Different types of inexpensive residual wastes were used: black rice husk ash, coconut husk ash, calcined retorted oil shale, and retorted oil shale. The fillers were characterized by thermogravimetric analysis and measurements of particle size distribution, specific surface area, and pore size distribution. The fillers were microporous materials with different chemical compositions, with average particle diameters varying from 5.6 to 76.6 μm, specific surface areas varying between 6 and 165 m²/g, and thermal stability at the polyurethane cure temperature (65°C). All composites were characterized by dynamic mechanical analysis, flexural tests, Shore A hardness tests, thermogravimetric analysis, and scanning electron microscopy analysis. Coconut husk ash, rice husk ash, and retorted oil shale presented better mechanical properties; nevertheless, coconut husk ash and rice husk ash had higher particle sizes, which caused bad dispersion of the filler in the matrix and resulted in nonhomogeneous composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Rheological characterization of UV‐curable epoxy systems: Effects of o‐Boehmite nanofillers and a hyperbranched polymeric modifier

An organo‐modified Boehmite (o‐Boehmite) was used to prepare nanocomposite UV‐curing coatings, based on a cycloaliphatic epoxy resin (3,4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexane carboxylate). A hyperbranched polymer (HBP) based on highly branched polyester, was also added to the resin, with the aim to modify its reactivity, such as a possible route to increase the toughness of the resin. Different amounts of the nanofiller and the HBP, ranging from 5 up to 20 wt % of resin, were dispersed into the resin in the presence of triarylsulfonium hexafluoroantimonate, as a photoinitiator for the UV curing of the resin. The rheological behavior of the formulations produced was studied as function of the shear rate and of the content of each filler using a cone and plate rheometer. A general increase in viscosity was observed with increasing the volume fraction of each filler and a moderate pseudoplastic behavior was observed when o‐Boehmite filler was added. A non‐Newtonian behavior was observed with the incorporation of the HBP. The viscosity of the epoxy/boehmite resin mixtures was analyzed as function of the nanofiller volume fraction. In the case of epoxy/hyperbranched resin mixtures, the Cross equation was used to predict the viscosity of each formulation as a function of the shear rate and an appropriate relationship to predict the viscosity of each formulation as a function of the filler volume fraction, was determined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Novel high‐solids pigmented coatings prepared from a new‐synthesized isophthalate‐based oligoester,a melamine resin,and various fillers

A new‐synthesized hydroxyl‐terminated isophthalate‐based liquid oligoester (L‐311), an hexakis(methoxymethylol)melamine resin, and various inert pigments (fillers) such as either kaolins (Al₂O₃ · 2SiO₂ · 2H₂O) of different particle sizes (1.50 and 4.80 μm) or calcium metalsilicate (CaSiO₃) were used to prepare high‐solids pigmented coatings (PA and PW series, respectively). The physical, chemical, and mechanical properties (pencil hardness, Knoop hardness, flexibility, impact resistance, adhesion, gloss, solvent, and mar resistance) of the new‐formulated pigmented coatings were correlated to the chemical species of the filler, the filler's load and particle size, the quantity of the crosslinker, and the introduction of large particle size colloidal silica into the coating. For measuring the mar resistance of the pigmented coatings, the Taber abrasion method was applied and the inverse wear index, F [=I^?1, cycles/cg (wear index l, weight loss (cg) per number of cycles)], was directly related to the mar resistance. Either when kaolins or calcium metalsilicates were used as fillers, the Knoop hardness, the impact, and mar resistance of the films were affected from the filler's load, whereas the quantity of melamine resin (crosslinker) affected the knoop hardness, the gloss, and the mar resistance. The fillers' particle size and the introduction of large particle colloidal silica affected mainly the mar resistance and the gloss, respectively. The pencil hardness of the PW‐pigmented coatings series (F‐2H) was higher than that of the PA‐series (B‐HB). The chemical composition of the inert pigment proved to be a very important parameter in the preparation of pigmented coatings with specific properties that aim to meet modern and particular demands for various end‐up uses. All the new‐formulated high‐solids (nonvolatiles by weight ～ 70%) pigmented coatings (PA and PW series) presented excellent adhesion (5B), flexibility (> 32%), methyl ethyl ketone (MEK) resistance (>200 rubs), high pencil hardness, good knoop hardness, and very good impact resistance (from 100 up to 160 in.‐lb), independently of the species of the filler (kaolins or calcium metalsilicate). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 576–590, 2002; DOI 10.1002/app.10309     

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.     

Synergistic effect of boron nitride and tetrapod‐shaped zinc oxide whisker hybrid fillers on filler networks in thermal conductive HDPE composites

In this paper, in order to investigate and predict the synergistic effect of the tetra‐needle‐shaped zinc oxide whisker (T‐ZnO) and boron nitride (BN) hybrid fillers in the thermal conductive high‐density polyethylene (HDPE) composites, the filler networks were studied through dynamic rheological measurement. Moreover, the crystallinity of the HDPE in the composites, and the thermal and electrical conductivity of the composites were also investigated. It was found that when the ratio of the BN and T‐ZnO in hybrid fillers was 20:10, the HDPE/hybrid fillers composite not only had the highest thermal conductivity but also can maintain the electrically insulating. Furthermore, the gel point of the HDPE/hybrid fillers composites was 11.2 wt%, and it was close to the 10 wt%. Therefore, the synergistic effect of the T‐ZnO and BN hybrid fillers in the HDPE/hybrid fillers composites can be successfully predicted through dynamic rheology date. Simultaneously, the Scanning electron microscope results showed that the T‐ZnO and BN particles can contact each other to form the thermal conductive paths so that the thermal conductivity of the HDPE can be enhanced through addition of the hybrid fillers. In addition, it was also found that the improved thermal conductivity of the HDPE/hybrid fillers composites was not because of a change in the crystallinity of the HDPE in the HDPE/hybrid fillers composites. POLYM. COMPOS., 38:1902–1909, 2017. © 2015 Society of Plastics Engineers     

Preparation,characterization, and improvement of hollow epoxy particle‐toughened vinyl ester composites for high‐end applications

Spherical hollow epoxy particles (HEPs) that can serve as advanced reinforcing fillers for vinyl ester thermosets were prepared using the water‐based emulsion method. The HEP fillers were incorporated into the vinyl ester matrices at different loading amounts, ranging from 0 to 9 wt %, to reinforce and toughen the vinyl ester composite. The optimum mechanical properties of the HEP‐toughened epoxy composite can be achieved by the addition of 5 wt % HEP filler into the vinyl ester matrices. The toughening and strengthening of the epoxy composites involved the interlocking of vinyl ester resins into the pore regions on the HEP fillers. The toughening and interlocking mechanisms of HEP‐toughened vinyl ester composites were also proposed and discussed. The addition of HEP fillers into vinyl ester matrices increased the glass transition temperature (T_g) and thermal stability of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Polymer composites with enhanced thermal conductivity via oriented boron nitride and alumina hybrid fillers assisted by 3-D printing

Herein, oriented boron nitride (BN)/alumina (Al₂O₃)/polydimethylsiloxane (PDMS) composites were obtained by filler orientation due to the shear-inducing effect via 3-D printing. The oriented BN platelets acted as a rapid highway for heat transfer in the matrix and resulted in a significant increase in the thermal conductivity along the orientation direction. Extra addition of spherical Al₂O₃ enhanced the fillers networks and resulted in the dramatic growth of slurry viscosity. This, together with filler orientation induced the synergism and provided large increases in the thermal conductivity. A high orientation degree of 90.65% and in-plane thermal conductivity of 3.64 W/(m∙K) were realized in the composites with oriented 35 wt% BN and 30 wt% Al₂O₃ hybrid fillers. We attributed the influence of filler orientation and hybrid fillers on the thermal conductivity to the decrease of thermal interface resistance of composites and proposed possible theoretical models for the thermal conductivity enhancement mechanisms.     

Effect of filler loading on the mechanical properties of crosslinked 1,2,3‐triazole polymers

The effect of filler loading on the mechanical properties of crosslinked triazole polymers obtained by polymerization of E300 dipropiolate ( 1 ) with diazide ( 2 ) obtained from tetraethylene glycol using tetraacetylene functionalized crosslinker ( 3 ) was studied systematically. Aluminum (10–14 μm) was used as the primary filler during the formulations; the effect of secondary fillers such as aluminum (<75 μm), NaCl (45–50 and 83–105 μm) was studied with the increase in the total filler loading. The modulus of the aluminum‐filled crosslinked triazole polymers increases with the increase in the filler content while using either particle sized aluminum powder. The use of Al (particle size <75 μm) and NaCl (particle size 45–50 μm and 83–105 μm) as secondary or additional fillers while using aluminum (10–14 μm) as the main filler, has a diminishing effect on the modulus and strain of the crosslinked triazole polymers. Triazole polymers described herein have the ability to wet and adhere to large quantities of these inorganic salts and thus maintain mechanical properties of the composite comparable to typical polyurethane elastomeric matrices, regardless of the chemistry of the particulate filler, which imparts an important and necessary binder characteristic for energetic composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010