Mechanical and tribological properties of polyoxymethylene modified with nanoparticles and solid lubricants

Polyoxymethylene (POM) composites modified with nanoparticles, polytetrafluoroethylene (PTFE) and MoS₂ were prepared by a twin‐screw extruder. The effect of nanoparticles and solid lubricant PTFE/MoS₂ on mechanical and tribological properties of the composites were studied. Tribological tests were conducted on an Amsler friction and wear tester using a block‐on‐ring arrangement under dry sliding and oil lubricated conditions, respectively. The results showed that generally speaking POM nanocomposites had better stiffness and tribological properties than corresponding POM composites attributed to the high surface energy of nanoparticles, except that the tensile strength of three composites and dry‐sliding tribological properties of POM/3%Al₂O₃ nanocomposite decreased due to the agglomeration of nanoparticles. Tribological properties differed under dry sliding and oil lubricated conditions. The friction coefficient and wear volume of POM nanocomposites under oil lubricated condition decreased significantly. The increased deformation resistance supported the increased wear resistance of POM nanocomposites. POM/PTFE/MoS₂/3%Al₂O₃ nanocomposite had the best mechanical and tribological properties of all three composites, which was attributed to the synergistic effect of nanoparticles and PTFE/MoS₂. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Tribological properties of bismaleimide composites with surface‐modified SiO2 nanoparticles

In this article, the surface of SiO₂ nanoparticles was modified by silane coupling agent N‐(2‐aminoethyl)‐γ‐aminopropylmethyl dimethoxy silane. The bismaleimide nanocomposites with surface‐modified SiO₂ nanoparticles or unmodified SiO₂ nanoparticles were prepared by the same casting method. The tribological performance of the nanocomposites was studied on an M‐200 friction and wear tester. The results indicated that the addition of SiO₂ nanoparticles could decrease the frictional coefficient and the wear rate of the composites. The nanocomposites with surface‐modified SiO₂ nanoparticles showed better wear resistance and lower frictional coefficient than that with the unmodified nanoparticles SiO₂. The specific wear rate and the steady frictional coefficient of the composite with 1.0 wt % surface‐modified SiO₂ nanoparticles are only 1.8 × 10^?6 mm³/N m and 0.21, respectively. The dispersion of surface‐modified SiO₂ nanoparticles in resin matrix was observed with transmission electron microscope, and the worn surfaces of pure resin matrix and the nanocomposites were observed with scanning electron microscope. The different tribological behavior of the resin matrix and the filled composites should be dependent on their different mechanical properties and wear mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tribological mechanism improving the wear resistance of polyurethane/epoxy interpenetrating polymer network via nanodiamond hybridization

The excellent synergistic effect of physical/mechanical properties of polyurethane/epoxy (PU/EP) interpenetrating polymer network (IPN) and the validity of nanofilling have one potential to improve the wear resistance of polymeric materials. With the aim of practical application, PU/EP IPN nanocomposites are prepared with nanodiamond (ND) as a reinforcing additive. Results showed the uniform thermal stability and the excellent compatibility between PU and EP in ND‐hybridized PU/EP IPN. Simultaneously, ND particles work as crosslinked points improving the physical/mechanical properties of ND‐hybridized PU/EP IPN, especially the wear resistance. The measurement of tribological property and the scanning electron microscope indicated that the wear resistance is able to be improved a lot by the formation of IPN and by the addition of ND. Consequently, the tribological mechanism of PU/EP IPN nanocomposites comes into being. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40244.     

Structural,thermal, and tribological properties of intercalated polyoxymethylene/molybdenum disulfide nanocomposites

Intercalated polyoxymethylene (POM)/molybdenum disulfide (MoS₂) nanocomposites were prepared by in situ intercalation/polymerization. The structures of the composites were characterized by means of powder X‐ray diffraction (XRD) and transmission electron microscopy. The XRD pattern showed that the polymer was inserted into the MoS₂ galleries. The interlayer spacing of the intercalated phase increased from 6.15 to 11.18 Å. The thermal behavior of the composites was also investigated through thermogravimetric analysis. The results show that the heat resistance of the intercalated composites decreased slightly. The tribological behavior of POM/MoS₂ was investigated on an MQ‐800 end‐face tirbometer under dry friction. The worn surfaces were observed by scanning electron microscopy. The results show that POM/MoS₂ presented better friction reduction and wear resistance, especially under high load. The friction mechanism of the nanocomposites is also discussed in association with X‐ray photoelectron spectroscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

In situ fabrication of CuO/UHMWPE nanocomposites and their tribological performance

Polymer nanocomposites present remarkably enhanced mechanical and tribological properties with respect to their matrices even at a low loading of nanofillers. Here, cupric oxide (CuO) nanoparticles (nano-CuO) were in situ filled into ultra-high-molecular-weight polyethylene (UHMWPE) to inhibit a possible agglomeration encountered in the preparation by mechanical mixing. The filled CuO nanoparticles were highly dispersed in UHMWPE with a reliable interface combination. The CuO nanoparticles in the matrix play a role for heterogeneous nucleation, resulting in an enhancement in degree of crystallinity of UHMWPE. The elastic modulus and the elongation at break of the nanocomposites also presented an improvement, indicating a good compatibility between the nano-CuO and the matrix. The average sliding friction coefficient of UHMWPE against 45^# steel was reduced by up to 34% after the in situ filling of CuO nanoparticles, and the wear mechanism was found to transform from adhesive to fatigue wear after the introduction of nano-CuO. It is concluded that the in situ filling can improve the dispersion of CuO nanoparticles in UHMWPE, and markedly promote the mechanical properties and tribological performance of UHMWPE. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47925.     

Tribological behaviors of polyurethane composites containing self‐lubricating microcapsules and reinforced by short carbon fibers

Self‐lubricating microcapsules containing methyl silicone oil as core materials, were prepared with poly(melamine‐formaldehyde) as shell material by in situ polymerization method. Combining with synergistic effect of the short carbon fibers (SCFs) which were systematically treated by liquid‐phase oxidation and chemical grafting, they were simultaneously adopted as reinforcing additives to improve the tribological and mechanical properties of polyurethane materials. The tribological behaviors and mechanical properties of the polyurethane composites have been investigated by a block‐on‐ring wear tester and electronic universal testing machine, respectively. The results indicate that the friction coefficient and wear rate of polyurethane composites without SCFs significantly decreased with increased self‐lubricating microcapsule concentration from 2.5 to 10 wt % due to the release of methyl silicone oil; meanwhile, the polyurethane composites filled with 10 wt % microcapsule and 15 wt % SCFs not only exhibited the lowest friction and wear behaviors, but also improved mechanical strength and thermal stability of polyurethane composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45331.     

Friction and wear properties of basalt fiber reinforced/solid lubricants filled polyimide composites under different sliding conditions

Short basalt fibers (BFs)‐reinforced polyimide (PI) composites filled with MoS₂ and graphite were fabricated by means of hot‐press molding technique. The tribological properties of the resulting composites sliding against GCr15 steel ring were investigated on a model ring‐on‐block test rig. The wear mechanisms were also comparatively discussed, based on scanning electron microscopic examination of the worn surface of the PI composites and the transfer film formed on the counterpart. Experimental results revealed that MoS₂ and graphite as fillers significantly improved the wear resistance of the BFs‐reinforced polyimide (BFs/PI) composites. For the best combination of friction coefficient and wear rate, the optimal volume content of MoS₂ and graphite in the composites appears to be 40 and 35%, respectively. It was also found that the tribological properties of the filled BFs/PI composites were closely related with the sliding conditions such as sliding speed and applied load. Research results show that the BF/PI composites exhibited better tribological properties under higher PV product. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Processing and tribology of thermoplastic polyurethane particulate composite materials

The processing, mechanical and tribological properties of wax containing thermoplastic polyurethane–filler composites were studied for different weight ratios of graphite, TiO₂, MoS₂, and ZrO₂ microparticles and SiO₂ nanoparticles. The composites were compounded by extrusion and processed by compression molding. The rheological, thermal, and mechanical properties were measured, and the wear characteristics were tested with ball-on-plate reciprocating tribometer tests under fixed friction conditions and then observed by scanning electron microscopy. Correlations between the friction, wear, and mechanical properties were observed, and their mechanisms are discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of filler functional groups on the mechanical properties and relevant mechanisms of polydicyclopentadiene nanocomposites

Filler functionlizetion is an important strategy to enhance the mechanical properties of polymer composites via the realization of polymer/filler coexists compatibly, interfacial bonding and efficacious load transfer between matrix and filler. In this study, to realize the tailored mechanical properties of polydicyclopentadiene (PDCPD) and to gain insight into the effect of functional groups on their properties, functionalized silica (f-SiO₂) with different functional groups is prepared and combined with PDCPD to produce composites. Compared with neat PDCPD, the yield strength of the composite with 0.20 wt% vinyl-SiO₂ decreases and the impact toughness enhances limitedly, whereas the tensile ductility improves by 16 times. For the case with 0.20 wt% phenyl-SiO₂, it is interestingly observed that the yield strength reinforces by 45.3% and the impact toughness increases remarkably by 222.8%. For the case containing 0.20 wt% ethyl-SiO₂, simultaneous promotion in terms of strength and toughness is achieved. More importantly, the reinforcing/toughening and reaction mechanisms of f-SiO₂/PDCPD composites are explored.     

The tribological properties of benzoxazine‐bismaleimides composites with functionalized nano‐SiO2

To improve the tribological properties of benzoxazine (BOZ) resin, bismaleimides (BMI) resin is chosen as organic phase, hyperbranched polysilane functionalized SiO₂ nanoparticles (HBPSi‐SiO₂) are chosen as inorganic modifiers to prepare HBPSi‐SiO₂/BOZ‐BMI composites using high shear and ultrasonic processes. The effect of content of HBPSi‐SiO₂ on the mechanical properties and tribological properties of the composites are investigated. The results show that suitable addition of HBPSi‐SiO₂ can largely enhance the impact strength, reduce the friction coefficient, and wear rate of BOZ‐BMI resin. Scanning electron microscopy is employed to research the wearing mechanism of materials. The severe wear of the BOZ pure resin is owing to fatigue wear, and the moderate wear of BOZ‐BMI resin is attributed to adhesive wear. While, the mild wear of the composites with HBPSi‐SiO₂ is due to abrasive wear. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Reinforcement of the mechanical properties in nitrile rubber by adding graphene oxide/silicon dioxide hybrid nanoparticles

Graphene oxide (GO) and silicon dioxide (SiO₂) nanoparticles have been hybridized for improving the mechanical and dynamic mechanical properties of nitrile rubber (NBR). SiO₂ nanoparticles were homogeneously dispersed on the surface and between layers of GO, and the new hybrid nanoparticles formed (GO/SiO₂₎ had better thermal stability than GO. To evaluate the mechanical properties, GO/SiO₂/NBR nanocomposites were prepared by solution blending and mechanical solution methods. It was observed that tensile strength increased in a larger grade in GO/SiO₂/NBR nanocomposites than that in GO/NBR and SiO₂/NBR nanocomposites, while the elongation at break only changes smoothly. Moreover, dynamics measurements also indicated that the elasticity increased after adding GO/SiO₂ hybrid nanoparticles in NBR. From morphology's analysis of GO/SiO₂/NBR and GO/NBR nanocomposites, it is was conclude that the hybridization of the GO/SiO₂ was the determining factor for the reinforcement of the mechanical properties and elasticity of the NBR. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46091.     

Effects of carbon‐coated titanium dioxide nanoparticles as a photostabilizer on the photodegradation of rigid poly(vinyl chloride)

In this study, nanocomposites of rigid poly(vinyl chloride) (UPVC) using the synthesized carbon‐coated titanium dioxide (TiO₂) nanoparticles and commercial powder of titanium dioxide (with rutile structure) were prepared by melt blending. The presence of carbon‐coated TiO₂ nanoparticles with rutile structure in UPVC matrix led to an improvement in photo stability of UPVC nanocomposites in comparison with commercial UPVC. The photocatalytic degradation behavior of nanocomposites was investigated by measuring their structural changes, surface tension, and mechanical and morphological properties before and after UV exposure for 700 h. It was found that mechanical and physical properties of UPVC nanocomposites are not considerably reduced after UV exposure in the presence of carbon‐coated TiO₂ nanoparticles even in small percentage of nanoparticles in comparison with the presence of commercial TiO₂ particles. Therefore, it can be concluded that UPVC/TiO₂ nanocomposite with low content of carbon‐coated TiO₂ nanoparticles(0.25 wt %) illustrated high stability under light exposure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40228.     

Preparation of epoxy resin/CaCO3 nanocomposites and performance of resultant powder coatings

Epoxy resin/CaCO₃ nanocomposites were prepared by the methods of extruding, solution blending, and in situ and inclusion polymerization, respectively. The contents of nanoparticles in the nanocomposites were varied from 5 wt % to 15 wt %. Powder coatings with different content of nanoparticles were made from the nanocomposites. The results showed that the cupping property and impact resistance decreased with the increase of coating film thickness. The dispersion of nanoparticles in epoxy matrix affected the impact resistance and cupping property of the obtained coating films greatly. The coating films made from the nanocomposite prepared by in situ and inclusion polymerization showed that the best impact resistance and the maximum cupping property was achieved when nano‐CaCO₃ content was 5 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2656–2660, 2006     

Preparation and optical properties of transparent epoxy composites containing ZnO nanoparticles

Polymer nanocomposites are usually made by incorporating dried nanoparticles into polymer matrices. This way not only leads to easy aggregation of nanoparticles but also readily brings about opaqueness for nanocomposites based on functionally transparent polymers. In this letter, transparent ZnO/epoxy nanocomposites with high‐UV shielding efficiency were prepared via two simple steps: first, in situ preparation of zinc hydroxide (Zn(OH)₂)/epoxy from the reaction of aqueous zinc acetate (Zn(Ac)₂·2H₂O) and sodium hydroxide (NaOH) at 30°C in the presence of high‐viscosity epoxy resin; second, thermal treatment of the as‐prepared Zn(OH)₂/epoxy hybrid into ZnO/epoxy composites. Optical properties of the resultant ZnO/epoxy nanocomposites were studied using an ultraviolet–visible (UV–vis) spectrophotometer. The nanocomposites containing a very low content of ZnO nanoparticles (0.06 wt %) possessed the optimal optical properties, namely high‐visible light transparency and high‐UV light shielding efficiency. Consequently, the as‐prepared ZnO/epoxy nanocomposites are promising for use as novel packaging materials in lighting emitting diodes technology. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and properties of hybrid materials obtained by in situ copolymerization of ethylene and propylene in the presence of Al2O3 nanofibers (NafenTM) on catalytic system rac‐Et(2‐MeInd)2ZrMe2/isobutylalumoxane

Nanofibers of Al₂O₃ (commercial product Nafen^TM) with characteristic length of ～100 nm and diameter of ～10 nm were used to create new hybrid materials based on copolymer of ethylene and propylene. Nanocomposites were obtained by in situ catalytic copolymerization on the system rac‐Et(2‐MeInd)₂ZrMe₂/isobutylalumoxane. Formation of the nanocomposites with uniform distribution of Nafen nanoparticles in polymer matrix was confirmed by scanning and transmission electron microscopy. According to dynamic mechanical analysis data, introduction of the nanofiller in an amount of up to 3 wt % leads to an increase in glass transition temperature by 10 °C (E″) and by 21 °C (tan δ). The nanocomposites exhibit improved physico‐mechanical properties (tensile strength and elongation at break). It is shown that the nanofiller significantly improves resistance of the nanocomposite to the thermo‐oxidative and thermal degradation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44678.     

Role of copper alumina nanoparticles on the performance of polyvinylchloride nanocomposites

Poly(vinyl chloride) (PVC) nanocomposites with different contents of copper alumina (Cu-Al₂O₃) nanoparticles were prepared by the solution casting method. The effects of the nanoparticles on structural, thermal, electrical, contact angle and mechanical properties were thoroughly examined. The presence of Cu-Al₂O₃ in the macromolecular chain was confirmed through Fourier transform infrared (FTIR) spectroscopy. The X-ray diffraction (XRD) analysis of PVC nanocomposites showed the systematic arrangement of Cu-Al₂O₃ nanoparticles within the polymer, which indicated the higher crystallinity of the nanocomposites. The surface morphology of PVC was changed into hemispherical shaped particles by the inclusion of nanofiller was analyzed from SEM images. The glass transition temperature of the nanocomposites obtained from differential scanning calorimetry (DSC) was found to be increased with an increase in loading of nanoparticles in the polymer. The AC conductivity and dielectric studies revealed that the inclusion of nanofiller increases the electrical properties of the material and the composite with 7 wt.% sample showed the maximum conductivity and dielectric constant. The mechanical properties such as modulus, tensile strength, hardness, and impact properties of the PVC nanocomposites were significantly enhanced by the reinforcement of nanoparticles into the PVC matrix. The reinforcing mechanism behind the increase in tensile strength with the addition of nanoparticles was correlated with different theoretical models. The highest mechanical and electrical properties were observed for 7 wt.% Cu-Al₂O₃ loaded nanocomposite. Contact angle measurements of PVC with various loadings of Cu-Al₂O₃ nanofillers demonstrated that the nanoparticle attachment increased the hydrophobicity of the polymer matrix.     

Towards transparent PMMA/SiO2 nanocomposites with promising scratch‐resistance by manipulation of SiO2 aggregation followed by in situ polymerization

Poly(methyl methacrylate) grafted silica (SiO₂‐g‐PMMA) was synthesized via in situ suspension polymerization. To achieve better uniform dispersion, hexadecyltrimethylammonium bromide (CTAB) was introduced into xylene to manipulate SiO₂ aggregation. SiO₂‐g‐PMMA or SiO₂ was incorporated into PMMA matrix by in situ polymerization to prepare PMMA‐based nanocomposites. The effect of CTAB amount, in the range 0–35 wt %, on the modification was evaluated by DLS, TGA, and FTIR. Furthermore, morphology, optical, mechanical, and thermal properties of PMMA nanocomposites was characterized by SEM, UV–vis, DMA, and TGA. Owing to surface functionalization, SiO₂‐g‐PMMA exhibited far more excellent compatibility and dispersion in matrix compared with SiO₂. Surface hardness and thermal properties of nanocomposites were enhanced significantly under the premise in high transparency. It is expected that transparent nanocomposites with promising scratch‐resistance could have wide applications, such as airplane shielding window and daily furniture. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44612.     

Interfacial crystallization of low‐crystallinity elastomer incorporated by multi‐walled carbon nanotubes: Mechanical reinforcement,structural evolution and enhanced thermal stability

In this paper, we report interfacial crystallization in olefin block copolymer (OBC) with low crystallinity incorporated by multi‐walled carbon nanotubes (MWCNTs). A hybrid shish‐kebab (HSK) superstructure in nanocomposites is observed that MWCNTs act as central shish and OBC crystals grow perpendicular to the nanotubes axis. The mechanical properties of nanocomposites are significantly improved with incorporation of MWCNTs. The most ideal reinforcing and toughening effect is both observed in nanocomposites with MWCNTs content of 1 wt % that can increase tensile strength by 122% as well as elongation at break by 36%. Efficient load transfer are confirmed with in‐situ Raman spectra that G’ band of MWCNTs in OBC matrix exhibit a downshifting trend and symmetric broadening of line shape which reveals additional macroscale strain from axial extension of MWCNTs in nanocomposites, thus suggesting a certain load is carried by HSK superstructure. The structural evolution of OBC and nanocomposites are investigated by in‐situ wide‐angle X‐Ray Diffraction (WAXD). The Herman's orientation factor of nanocomposites with 2 wt % MWCNTs incorporation is lower than that of neat matrix at mall and intermediate strains, indicating a heterogeneous stress distribution and low compliance of HSK superstructure, which is consistent with in‐situ Raman results. Moreover, the nanocomposites presents significantly enhanced thermal stability. The onset decomposition temperature of nanocomposites with 3 wt % MWCNTs can be 60.2°C higher than that of neat OBC. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42368.     

Polystyrene/attapulgite nanocomposites prepared via in situ suspension polymerization with redox initiation system

A series of polymer–clay nanocomposites consisting of polystyrene (PS) and attapuglite (ATP) were prepared successfully. First, silane coupling agent containing aromatic tertiary amine groups was synthesized to functionalize ATP (M‐ATP). Then, PS nanocomposites with varied clay loadings were prepared via in situ suspension polymerization process with a redox initiation system consisting of aromatic tertiary amine and benzoyl peroxide. The synthesis of silane coupling agent and functionalization of ATP were confirmed by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectra, and X‐ray photoelectron spectroscopy. Mechanical properties, morphology, thermal stability, and rheological behavior of nanocomposites were investigated to illuminate the effects of M‐ATP on the structure and properties of nanocomposites. Field‐emission scanning electron microscope images revealed an ideal dispersion of M‐ATP and an enhanced toughness of nanocomposites. The improved interface interaction between M‐ATP and PS matrix endowed the nanocomposites with outstanding mechanical properties and thermal stability. The formation of hybrid network in the nanocomposites containing 3 wt % M‐ATP resulted in higher complex viscosity (η*), storage modulus (G′), and lower loss factor (tanδ) compared with the pristine PS and PS/ATP nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41567.     

The TiO2–Clay-LDPE Nanocomposite Packaging Films: Investigation on the Structure and Physicomechanical Properties

The role of nanoclays and TiO₂ nanoparticle loadings were investigated on low density polyethylene crystalline structure, in addition to studying packaging film properties such as barrier, thermal and mechanical properties. The polymer crystal study indicated for the orthorhombic crystal phase and about 20% lower degree of crystallinity for nanocomposites containing more than 2 wt.% TiO₂ nanoparticles. Based on the X-ray diffraction technique, the dispersion of nanoclays was improved to almost good degree of clay exfoliation with the company of 4 wt.% TiO₂ nanoparticles. In agreement with XRD results, the TEM morphological studies mainly suggest that TiO₂ has a helpful effect on nanoclay exfoliation. The increase in degradation temperature of nanocomposites may be attributed to the formation of inorganic char on polymer melt. The barrier properties of TiO₂/clay nanocomposite packaging films depend mainly on nanoclay loading with an unclear trend from TiO₂ nanoparticles. The increase in elastic modulus and the yield stress of nanocomposite films showed great effects on film mechanical properties by nanoclays.