Co-reporter:Yuanshi Xin;Tongsheng Li;Dafei Gong;Fanglin Xu;Mingming Wang
RSC Advances (2011-Present) 2017 vol. 7(Issue 11) pp:6323-6335
Publication Date(Web):2017/01/18
DOI:10.1039/C6RA27108A
A three-step strategy was employed to prepare a self-lubricating and anti-wear graphene oxide/nano-MoS2 (GO/nano-MoS2, abbreviated GMS) hybrid by chemical compounding as a novel multidimensional assembly. This development aims to overcome the high friction coefficient of GO/polymer composites and to explore the variations in the tribological properties stemming from the different nanoparticles immobilized on the GO surface. The as-prepared GMS was incorporated into a polyimide (PI) matrix to yield GMS/PI composites by in situ polymerization. The mechanical, thermodynamic, surface, and tribological properties of the GMS/PI composites were investigated, and the synergistic effects of the abovementioned properties between nano-MoS2 and GO were discussed in detail. A homogeneous dispersion of GMS, a suppressive and protective effect of graphene sheets, a rolling friction effect of the detached nano-MoS2 particles, and a transfer film composed of MoS2 were achieved herein, contributing to the enhanced tribological properties. The differences in the enhancement effects of nanohybrids can be mainly attributed to two aspects: the intrinsic characteristics of the assembled nanoparticles and the combinational structure of the multidimensional assemblies.
Co-reporter:Yuanshi Xin;Tongsheng Li;Fanglin Xu;Mingming Wang
RSC Advances (2011-Present) 2017 vol. 7(Issue 34) pp:20742-20753
Publication Date(Web):2017/04/10
DOI:10.1039/C7RA02149F
Modified graphene/carbon nanotube (abbreviated GCNT) assemblies were prepared by chemical compounding from amino-functionalized graphene (abbreviated MG) and carboxyl-functionalized multi-walled carbon nanotube (abbreviated MCNT). Diverse hybrid structures, such as graphene-shelled CNT microspheres, graphene/CNT interlayers and CNT-coated graphene nanosheets, have been obtained by adjusting the reaction ratio of the two precursor particles. The as-prepared GCNTs were incorporated into polyimide (PI) matrix to yield GCNT/PI composites by in situ polymerization. The mechanical, thermo-mechanical and tribological properties of GCNT/PI composites were investigated and synergistic effects in terms of lubrication and wear resistance have been acquired. The friction coefficient and wear rate decreased by 29.3% and 75.8%, respectively, with only 0.5 wt% addition of GCNT14 (WMG/WMCNT = 1 : 4), compared to virgin PI. The results indicate that combinational structure of multidimensional assemblies has a great influence on the enhancement performance and tribological mechanism of nanocomposites.
Co-reporter:Mingming Wang;Yuanshi Xin;Chao Su;Feng Xue;Fanglin Xu ;Tongsheng Li
Journal of Applied Polymer Science 2016 Volume 133( Issue 31) pp:
Publication Date(Web):
DOI:10.1002/app.43735
ABSTRACT
A two-step process, thermotropic liquid-crystalline polymer (TLCP) premixing with reduced graphene oxide (RGO) followed by blending with polyamide 6,6 (PA66), was used to prepare ternary TLCP/RGO/PA66 blends. The rheological behaviors, morphology, and mechanical properties of the blends were investigated. The results show that RGO migrated from the TLCP phase to the interface between the TLCP and PA66 phase during melt blending; this was due to a similar affinity of the RGO nanosheets to both component polymers. The dimensions of the dispersive TLCP domains were markedly reduced with the mounting RGO content; this revealed a good compatibilization effect of RGO on the immiscible polymers. The hierarchical structures of the TLCP fibrils were found in both the unfilled TLCP/PA66 blends and TLCP/RGO/PA66 blends. This supposedly resulted from the extensional and torsional action of unstable capillary flow. With the addition of RGO, the viscosities of the blends decreased further, and the fibrillation of TLCP and the mechanical performance of TLCP composites were both enhanced. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43735.
Co-reporter:Ting Huang, Tongsheng Li, Yuanshi Xin, Bocheng Jin, Zhongxin Chen, Chao Su, Haiming Chen and Steven Nutt
RSC Advances 2014 vol. 4(Issue 38) pp:19814-19823
Publication Date(Web):15 Apr 2014
DOI:10.1039/C4RA01964D
We design a feasible approach to prepare a self-lubricating and anti-wear graphene oxide/nano-polytetrafluoroethylene (GO/nano-PTFE, abbreviated GNF) hybrid additive by chemical compounding as a novel nano-solid lubricant. This proposal is to overcome the high friction coefficient of GO/polymer specimens for further increase in wear resistance. To explore the utility of GNF, it was incorporated into polyimide (PI) and epoxy (EP) matrices to yield GNF/PI and GNF/EP composites. The tribological properties and mechanism of GNF/polymer composites were investigated in detail. A nearly 60% reduction in friction coefficient and more than two orders of magnitude reduction in wear rate were obtained in both GNF/PI and GNF/EP composites with only 1 wt% GNF addition. Compared with unfilled polymers or polymers with individual fillers, the major increase in tribological properties of the GNF/polymer composites shows the synergy effect between nano-PTFE and GO. The increased tribological properties can be ascribed to four aspects: homogeneous GNF dispersion and strong interface, the increased mechanical properties, transfer film and tribological effect (protective effect and suppression effect) of GNF. It is demonstrated that this approach provides a novel self-lubricating and anti-wear nano-solid lubricant that greatly reduces wear and material loss.
Co-reporter:Haiming Chen;Chao Su;Ting Huang ;Tongsheng Li
Journal of Applied Polymer Science 2014 Volume 131( Issue 4) pp:
Publication Date(Web):
DOI:10.1002/app.39863
ABSTRACT
In this paper, polyetherimides (PEI) with two different calculated number-average molecular weights (Mn) of 5000 and 10,000 g/mol were synthesized and used to modify tetraglycidyl 4,4′-diaminodiphenylmethane. Three different morphologies (separated phase, bi-continuous phase, and phase inversion structure) were obtained by controlling molecular weights and content of PEI. Thermal and mechanical characterizations showed that addition of PEI resulted in an increase in thermal stability and tensile strength. Tensile strength of samples with bi-continuous phase was higher than those with separated phase or phase inversion structure. Influence of morphologies on tribology properties were studied by a ring-on-block wear tester. Higher wear resistance was achieved from samples with bi-continuous phase. It was found that wear life of samples with bi-continuous phase was almost 100% higher than that of samples with separated phase. This is clearly related to the change in thermal and mechanical properties caused by the change of morphologies. Scanning electron microscope observations of worn surfaces and wear debris of the tested samples showed that tribological behaviors and wear mechanisms were heavily dependent on morphologies. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39863.
Co-reporter:Ting Huang, Yuanshi Xin, Tongsheng Li, Steven Nutt, Chao Su, Haiming Chen, Pei Liu, and Zuliang Lai
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 11) pp:4878
Publication Date(Web):May 14, 2013
DOI:10.1021/am400635x
By taking advantage of design and construction of strong graphene–matrix interfaces, we have prepared modified graphene/polyimide (MG/PI) nanocomposites via a two-stage process consisting of (a) surface modification of graphene and (b) in situ polymerization. The 2 wt % MG/PI nanocomposites exhibited a 20-fold increase in wear resistance and a 12% reduction in friction coefficient, constituting a potential breakthrough for future tribological application. Simultaneously, MG also enhanced thermal stability, electrical conductivity, and mechanical properties, including tensile strength, Young’s modulus, storage modulus, and microhardness. Excellent thermal stability and compatibility of interface, strong covalent adhesion interaction and mechanical interlocking at the interface, as well as homogeneous and oriented dispersion of MG were achieved here, contributing to the enhanced properties observed here. The superior wear resistance is ascribed to (a) tribological effect of MG, including suppression effect of MG in the generation of wear debris and protective effect of MG against the friction force, and (b) the increase in mechanical properties. In light of the relatively low cost and the unique properties of graphene, the results of this study highlight a pathway to expand the engineering applications of graphene and solve wear-related mechanical failures of polymer parts.Keywords: design and construction of interface; modified graphene; polyimide nanocomposites; reinforcing effect; tribological effect;
Co-reporter:Haiming Chen;Renguo Lv;Pei Liu;Hongyan Wang;Zhongyuan Huang;Ting Huang ;Tongsheng Li
Journal of Applied Polymer Science 2013 Volume 128( Issue 3) pp:1592-1600
Publication Date(Web):
DOI:10.1002/app.37890
Abstract
In this work, poly(amide-amidic acid) (PAA) was used to modify tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM)/4,4′-diaminodiphenylsulfone (DDS) system. Results of non-isothermal differential scanning calorimetry analysis indicated that PAA played a role of catalyst during the process of the curing reaction. The curing mechanism was studied by Fourier transform infrared spectroscopy, showing that the PAA acted as a co-curing agent in the system. The glass transition temperature decreased firstly and then increased with the increase of the PAA content. PAA equally rendered TGDDM more fire resistant with higher char yield. On examining the fracture surface morphology using scanning electron microscopy, it was observed that there was no obvious phase separation when the content of PAA was less than 20 phr (per hundred weight of TGDDM/DDS resin), however, phase separation was observed when the content of PAA was 25 and 30 phr. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Co-reporter:Ting Huang, Tongsheng Li, Yuanshi Xin, Pei Liu, Chao Su
Wear 2013 Volume 306(1–2) pp:64-72
Publication Date(Web):30 August 2013
DOI:10.1016/j.wear.2013.06.010
•Hybrid fabric–PEI composites were prepared by dip-coating and subsequently thermal curing.•Modification of PEI had a great influence on the properties of hybrid fabric composites.•Mechanical properties were improved, thereby enhancing wear resistance.•Modified PEI afforded excellent interface, therefore obtaining better tribological properties.•Best mechanical and tribological properties were obtained by the modification of PEI.Modified polyetherimide (PEI) resins were prepared by a series of phenylethynyl terminated etherimide (PTEI) oligomers with different calculated Mn. Hybrid fabric–modified PEI composites were fabricated by dip-coating and subsequently thermal curing. For comparison, hybrid fabric–unmodified PEI composite was also prepared. Modification of PEI had a great influence on the performances of hybrid fabric composites. Mechanical characterizations indicated that there exhibited a remarkable improvement in the Rockwell hardness and fabric bonding strength. The tribological properties of hybrid fabric composites were investigated by a MPX-2000A friction and wear tester with an end-face contact mode. The best tribological properties of hybrid fabric composites were obtained when modified PEI was prepared by PTEI oligomers with the calculated Mn of 5000 g/mol. The friction and wear mechanisms were explored by a combination of mechanical analyses and scanning electron microscope (SEM) observations of worn surfaces and wear debris. Note that modified PEI afforded excellent interface between fabric and resin in the corresponding fabric composites. This can ensure outstanding mechanical properties and significantly restrain the initiation and growth of cracks on the worn surfaces, thereby improving wear resistance.
Co-reporter:Ting Huang, Renguo Lu, Chao Su, Hongna Wang, Zheng Guo, Pei Liu, Zhongyuan Huang, Haiming Chen, and Tongsheng Li
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 5) pp:2699
Publication Date(Web):April 11, 2012
DOI:10.1021/am3003439
Herein, we have developed a rather simple composite fabrication approach to achieving molecular-level dispersion and planar orientation of chemically modified graphene (CMG) in the thermosetting polyimide (PI) matrix as well as realizing strong adhesion at the interfacial regions between reinforcing filler and matrix. The covalent adhesion of CMG to PI matrix and oriented distribution of CMG were carefully confirmed and analyzed by detailed investigations. Combination of covalent bonding and oriented distribution could enlarge the effectiveness of CMG in the matrix. Efficient stress transfer was found at the CMG/PI interfaces. Significant improvements in the mechanical performances, thermal stability, electrical conductivity, and hydrophobic behavior were achieved by addition of only a small amount of CMG. Furthermore, it is noteworthy that the hydrophilic-to-hydrophobic transition and the electrical percolation were observed at only 0.2 wt % CMG in this composite system. This facile methodology is believed to afford broad application potential in graphene-based polymer nanocomposites, especially other types of high-performance thermosetting systems.Keywords: chemically modified graphene; covalent bonding; efficient stress transfer; interfacial interactions; oriented distribution; polyimide;
Co-reporter:Haiming Chen;Renguo Lu;Pei Li;Hongyan Wang;Ting Huang;Zhongyuan Huang ;Tongsheng Li
Journal of Applied Polymer Science 2012 Volume 125( Issue 4) pp:2854-2860
Publication Date(Web):
DOI:10.1002/app.36430
Abstract
A novel curing agent, poly (amide-amidic acid) (PAA), was used to cure tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM). The initial cure and exothermic peak temperatures increased with increase in PAA content. The mechanism for the cure of TGDDM/PAA was proposed which involved, besides TGDDM cure, PAA imidization in the system. Examination of the morphology of the fractured surface using scanning electron microscopy showed that curing with PAA improved more the fracture toughness as compared to the conventional 4,4′-diaminodiphenylsulfone (DDS), and rendered TGDDM more fire resistant with higher char yield. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Co-reporter:Ting Huang, Pei Liu, Renguo Lu, Zhongyuan Huang, Haiming Chen, Tongsheng Li
Wear 2012 Volumes 292–293() pp:25-32
Publication Date(Web):15 July 2012
DOI:10.1016/j.wear.2012.06.003
The incorporation of 4-phenylethynylphthalic anhydride (4-PEPA) was utilized to synthesize a series of phenylethynyl terminated oligomers, according to different calculated number-average molecular weight (Mn). Modified polyetherimide (PEI) resins were prepared by the thermal curing reaction of phenylethynyl terminated etherimide oligomers. For comparison, unmodified PEI was also prepared. Thermal, macro- and micro-mechanical characterizations showed that the incorporation of phenylethynyl terminated agent resulted in a significant increase in glass transition temperature (Tg), tensile strength and microhardness. The tribological properties of PEI specimens were evaluated on a reciprocating friction and wear testing machine. Higher wear resistance was achieved by the incorporation of phenylethynyl terminated agent. Furthermore, wear rate of modified PEI prepared from the oligomers with the calculated Mn of 5000 g/mol was about five times lower than that of unmodified PEI. At least for the range of this study, while increasing calculated Mn of oligomers, wear rate of modified PEI initially decreased sharply and then increased slightly. This is clearly related to the change in the macro- and micro-mechanical properties. Scanning electron microscope (SEM) observations of worn surfaces showed that type of wear changed from abrasive wear of unmodified PEI into fatigue wear.Graphical abstractHighlights► Modified PEI resins were prepared from different calculated Mn oligomers. ► Tg, macro- and micro-mechanical properties were enhanced by phenylethynyl terminated agent. ► The improvement in macro- and micro-mechanical properties led to obtain better wear resistance. ► Best wear resistance was obtained as ca. five times more than that of unmodified PEI. ► Type of wear changed from abrasive wear into fatigue wear.
Co-reporter:Pei Liu, Renguo Lu, Ting Huang, Peihong Cong, Sisi Jiang, Tongsheng Li
Wear 2012 Volume 289() pp:65-72
Publication Date(Web):15 June 2012
DOI:10.1016/j.wear.2012.04.013
Polytetrafluoroethylene (PTFE) fiber and fabric homocomposites consisting of a PTFE fiber/fabric reinforcing element and a PTFE matrix were fabricated. The tensile and tribological properties of PTFE homocomposites were tested. It is found that the self-reinforcements have improved the tensile and tribological properties of PTFE significantly. PTFE fiber homocomposite with 40 wt% fiber (IH40) performed the best among the fiber homocomposites. The tensile strength of IH40 was twice that of the unfilled PTFE. Compared to the unfilled PTFE, the friction coefficient and wear rate of IH40 decreased 11% and 53%, respectively. PTFE fabric homocomposites behaved better than fiber based ones. The fabric homocomposite with 60% fabric prepared by impregnation technique (AH60-I) was superior to the one by stacking technique. The tensile strength of AH60-I was as high as 3.5 times that of the unfilled PTFE. The friction coefficient and wear rate of AH60-I decreased 30% and 77%, respectively. The reinforcing and wear mechanisms were discussed based on the test results and the observations of tensile failure surfaces, wear debris and worn surfaces.Highlights► The tensile strength and tribological properties of PTFE were significantly improved through fiber/fabric self-improvement. ► PTFE fabric homocomposites were observed to perform better than fiber ones in both tensile and tribological properties. ► Impregnation technique was superior to stacking technique in the preparation of PTFE fabric homocomposites. ► Fiber intertwining and the interfacial adhesion were the main factors that affected the tensile strength. ► Fiber/fabric self-reinforcement influenced the formation process of wear debris and thus enhanced the wear resistance.
Co-reporter:Pei Liu, Ting Huang, Renguo Lu, Tongsheng Li
Wear 2012 Volume 289() pp:17-25
Publication Date(Web):15 June 2012
DOI:10.1016/j.wear.2012.04.021
Various modified carbon fabric (CF)/polytetrafluorothylene (PTFE) composites were prepared by means of CF surface treatment, i.e. air-plasma treatment and HNO3 etching, introduction of nano-TiO2 and combined methods. The composites were evaluated for their tribological behaviors and the worn surfaces were observed by a scanning electron microscope (SEM) to understand the mechanism. The water contact angle and the surface topography of the untreated and surface-treated CF were also analyzed. It was found that the surface treatment improved the surface hydrophilicity and changed the surface topography of CF, which contributed to improve the interfacial adhesion of the composites and hence the tribological behaviors. The inclusion of 4 wt% nano-TiO2 provided the optimum wear resistance among the nano-TiO2 modified composites. There was a cooperating effect of CF air-plasma treatment and 4 wt% nano-TiO2 modification to the wear-reduction of the composites.Highlights► Air-plasma and HNO3 treatment of carbon fabric improved the surface hydrophilicity and changed the surface topography. ► Fabric surface treatment improved the interfacial bonding and tribological behaviors of carbon fabric/PTFE composites. ► Nano-TiO2 modification improved the wear resistance of the composites and 4 wt% was the optimum. ► Air air-plasma treatment and nano-TiO2 modification had a cooperating effect to the wear-reduction.
Co-reporter:Hongyan Wang, Renguo Lu, Ting Huang, Yuning Ma, Peihong Cong, Tongsheng Li
Materials Science and Engineering: A 2011 528(22–23) pp: 6878-6886
Publication Date(Web):
DOI:10.1016/j.msea.2011.05.049
Co-reporter:Qing-Yi Peng, Pei-Hong Cong, Xu-Jun Liu, Tian-Xi Liu, Shu Huang, Tong-Sheng Li
Wear 2009 Volume 266(7–8) pp:713-720
Publication Date(Web):25 March 2009
DOI:10.1016/j.wear.2008.08.010
Poly(vinylidene fluoride) (PVDF) nanocomposites with different content of nanoclay were prepared by melt-intercalation method. The tribological behaviors of the PVDF/clay nanocomposites against 45# carbon steel ring were evaluated on a block-on-ring type (M-2000) wear tester. Transmission electron microscopy (TEM) observation showed the dispersion of nanoclay in PVDF matrix. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis found that nanoclay incorporation induced the PVDF crystal form to transform from α- to β-phase, and hence increased the materials polarity. Differential scanning calorimetry (DSC) analysis verified that the crystallinity of the nanocomposites decreased with the increasing nanoclay content. Nanoclay at 1–2 wt.% was effective for improving the tribological properties of neat PVDF, because the nanoclay at the low content may act as the reinforcing element to bore load and thus decrease the plastic deformation. The nanocomposite containing 5 wt.% nanoclay exhibited relatively high wear, weak compatibility between nanoclay and PVDF and also the decreased crystallinity may be responsible for the result.
Co-reporter:Bin-Bin Jia, Xu-Jun Liu, Pei-Hong Cong, Tong-Sheng Li
Wear 2008 Volume 264(7–8) pp:685-692
Publication Date(Web):15 March 2008
DOI:10.1016/j.wear.2007.06.004
The friction and wear behaviors of various polymer–polymer combinations were examined by means of a pin-on-disc type apparatus. The worn surfaces of the polymers were observed by using Scanning Electron Microscope (SEM). The relationships between the tribological properties and cohesive energy density (CED) of the two mated polymers were found. For the similar polymer combinations, the increasing CED of the polymers associated with an increasing friction coefficient but a decreasing specific wear rate. For the dissimilar polymer combinations, the friction coefficient was found to relate to the absolute value of the CED difference of the two mated polymers, that was, the greater the CED difference of the two mated polymers was, the higher the friction coefficient was. The specific wear rates of the polymers increased with the increasing CED of the mated polymers for dissimilar polymer–polymer combinations. Coarse worn surfaces were observed when the two mated polymers with little difference in CED value. It was concluded that the adhesion between the two mated polymers was a main factor for controlling the friction property of a polymer–polymer sliding combination, and the polymer wear was closely related to its shear strength. The reasons why the tribological properties of polymer–polymer combinations related to the CED of polymers were also discussed.
Co-reporter:Peihong Cong, Fei Xiang, Xujun Liu, Tongsheng Li
Wear 2008 Volume 265(7–8) pp:1100-1105
Publication Date(Web):20 September 2008
DOI:10.1016/j.wear.2008.03.004
The morphology and microstructure of PA46 wear debris and transfer film were studied by using scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FT-IR) and X-ray diffractometer (XRD) for understanding the physical and chemical changes of PA46 caused by friction. An acid-eroding method was used to peel the transfer film from the mated steel ring surface. It was found that PA46 molecules happened directional arrange along the friction direction both in the transfer film and on the worn surface. PA46 formed two different shapes of wear debris: belt-like and spiral rod-like wear debris, which related to different wear mechanisms of PA46 during sliding process. Compared to the PA46 bulk, the crystal state in the transfer film and wear debris decreased and the amorphous structure increased. The main wear mechanisms of PA46 against steel were suggested to be adhesive wear and melting flow.
Co-reporter:Peihong Cong, Fei Xiang, Xujun Liu, Tongsheng Li
Wear 2008 Volume 265(7–8) pp:1106-1113
Publication Date(Web):20 September 2008
DOI:10.1016/j.wear.2008.03.005
PA46/HDPE polyblends with different component ratios and the same content of compatibilizer HDPE-g-MAH were prepared to investigate the main influence factors for the tribological properties of the polyblends. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used for investigating the phase structure and crystalline characteristics of the polyblends, respectively. The friction coefficients of all PA46/HDPE blends were as low as 0.21–0.22, which were near the friction coefficient of pure HDPE, and much lower than that of pure PA46 (0.77). The wear of PA46/HDPE (8/2), which contained less HDPE, was much lower than that of the polyblends which had more HDPE component. DSC and XRD analysis results suggested that the crystalline form may be the main factor to influence the wear property of PA46/HDPE polyblends. γPA46 phase caused high wear and large sheet-like debris because of its low inherent strength, αPA46 and βPA46 phases associated with low wear, which accompanied by smoother worn surface and small fragment-like wear debris.
Co-reporter:Zhaobin Chen;Xujun Liu;Renguo Lü;Tongsheng Li
Journal of Applied Polymer Science 2007 Volume 105(Issue 2) pp:602-608
Publication Date(Web):28 MAR 2007
DOI:10.1002/app.25999
The mechanical and tribological properties of carbon fiber (CF) reinforced polyamide 66 (PA66)/polyphenylene sulfide (PPS) blend composite were studied in this article. It was found that CF reinforcement greatly increases the mechanical properties of PA66/PPS blend. The friction coefficient of the sample decreases with the increase of CF content. When CF content is lower (below 30%), the wear resistance is deteriorated by the addition of CF. However, the loading of higher than 30% CF significantly improves the tribological properties of the blend. The lowest friction coefficient (0.31) and the wear volume (1.05 mm3) were obtained with the PA66/PPS blend containing 30% CF. The transfer film and the worn surface formed by sample during sliding were examined by scanning electron microscopy. The observations revealed that the friction coefficient of PA66/PPS/CF composite depends on the formation and development of a transfer film on the counterface. The abrasive wear caused by ruptured CFs (for lower CF content) and the load bearing ability of CFs (for higher CF content) are the major factors affecting the wear volume. In addition, the improvements of mechanical properties, thermal conductivity, and self-lubrication of bulk CFs are also contributed to the wear behavior of PA66/PPS/CF composite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Co-reporter:Xiaoxia Liu;Tongsheng Li;Renguo Lv;Peihong Cong;Xujun Liu
Journal of Applied Polymer Science 2007 Volume 106(Issue 2) pp:1332-1336
Publication Date(Web):12 JUL 2007
DOI:10.1002/app.26629
Drawn polytetrafluoroethylene (PTFE) with different draw ratio and sliding directions were investigated using a pin-on-disc tester. The anisotropy of tribological properties for drawn PTFE was found and the lowest friction coefficient and wear rate were reached when sliding along draw direction. The higher the orientation degree was, the smaller the friction coefficient and the wear rate were. The morphologies of the samples and debris were characterized by scanning electron microscope. The results showed that the fiber structure of drawn PTFE was formed and the morphologies of debris were different from undrawn PTFE. The results indicated that the bulk orientation structure of drawn PTFE played an important role on its tribological properties. The shear force was parallel with the oriented fibrils formed by drawing when sliding along draw direction and a better smoothing worn surface occurred easily, which resulted in the low friction coefficient. The fiber formed by drawing prevented effectively the large flake-like debris from formation, which reduced the wear rate of drawn PTFE. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Co-reporter:Shi-Quan Lai;Li Yue
Journal of Applied Polymer Science 2007 Volume 106(Issue 5) pp:3091-3097
Publication Date(Web):14 AUG 2007
DOI:10.1002/app.25337
Two types of representative nanometer materials, i.e., fibroid nanometer attapulgite and approximate spherical ultrafine diamond, were selected as fillers of polytetrafluoroethylene (PTFE) to study the mechanism of the wear-reducing actions of the fillers in PTFE composites. The friction and wear tests were performed on a block-on-ring wear tester under dry sliding conditions. Differential scanning calorimetry (DSC) was used to investigate material microstructure and to examine modes of failure. No significant change in coefficient of friction was found, but the wear rate of PTFE composites was orders of magnitude less than that of pure PTFE. DSC analysis revealed that nanometer attapulgite and ultrafine diamond played a heterogeneous nucleation role in PTFE matrix and consequently resulted in increasing the crystallinity of PTFE composites. Moreover, the PTFE composite with higher heat absorption capacity and crystallinity exhibited improved wear resistance. A propositional “sea-frusta” frictional model explained the wear mechanism of filler action in reducing the wear of PTFE polymer, i.e., fillers in the PTFE matrix effectively reduced the size of frictional broken units for PTFE composites and restrained the flowability of the units, as well as supporting the applied load. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Co-reporter:Xiao-Xia Liu, Tong-Sheng Li, Xu-Jun Liu, Ren-Guo Lv, Pei-Hong Cong
Wear 2007 Volume 262(11–12) pp:1414-1418
Publication Date(Web):10 May 2007
DOI:10.1016/j.wear.2007.01.021
Measurements of the friction coefficient of oriented polytetrafluoroethylene (PTFE) have been made and the results indicate that the friction coefficient of drawn PTFE is dependent on the oriented direction. The worn surfaces were observed using an atomic force microscopy (AFM). The crystallinity of the transfer film was determined using differential scanning calorimeter (DSC). Friction orientation was found to be an important character of PTFE tribology. The friction-induced orientation occurred on the worn surfaces and the transfer films with high crystallinity were formed on the counterparts, which was one of the causes for the relatively steady friction coefficient in the sliding process. However, the formation of the friction-induced orientation on the worn surfaces and the transfer film did not change the anisotropy of the friction coefficient for drawn PTFE under our experimental conditions. Although this result meant that the bulk-oriented structures of PTFE play an important role on its friction processes, the formation of better friction-induced orientation could result in the lower friction coefficient.
Co-reporter:Shi-Quan Lai, Tong-Sheng Li, Fan-Dong Wang, Xu-Jun Li, Li Yue
Wear 2007 Volume 262(9–10) pp:1048-1055
Publication Date(Web):10 April 2007
DOI:10.1016/j.wear.2006.10.007
In order to investigate the effect of silica size on the friction and wear behaviors of PI hybrids, polyimide/silica (PI/SiO2) hybrids with different size of silica were successfully synthesized through an in situ sol–gel reaction from pyromellitic dianhydride-4,4′-oxydianiline (PMDA—ODA) and tetraethoxysilane (TEOS). The size of silica in the hybrids was 100–800 nm. The friction and wear test for pure PI and its hybrids was carried out on a ball-on-disc wear tester under dry sliding conditions. Tensile tests on the PI/SiO2 hybrids showed that the strength and toughness of PI/SiO2 hybrids were improved simultaneously when the size of silica was less than 300 nm. The friction coefficient and wear rate of the PI hybrids firstly decreased and then increased with increasing the size of silica. The friction coefficient of the hybrid with 100 nm SiO2 was the lowest and ca.20% lower in contrast with that of pure PI. However, the lowest wear rate was recorded for the hybrid with 300 nm SiO2, ca.20% lower than that of neat PI. These behaviors were attributed to the size effect of silica in PI matrix. Scanning electron microscopy (SEM) revealed that an appropriate size of silica in PI matrix could effectively reduce adhesive wear of PI and restrain the formation of bigger debris.
Co-reporter:Zhaobin Chen;Xujun Liu;Tongsheng Li;Renguo Lü
Journal of Applied Polymer Science 2006 Volume 101(Issue 2) pp:969-977
Publication Date(Web):25 APR 2006
DOI:10.1002/app.22061
The mechanical and tribological properties of 70 vol % PA66/30 vol % PPS blend filled with different content of polytetrafluoroethylene (PTFE) were studied in this paper. It was found that the addition of PTFE impairs the mechanical properties of PA66/PPS blend, but greatly increases the wear resistance and decreases the friction coefficient. When PTFE content exceeds 20 vol %, the friction coefficient of composite is minimum (0.15) and lower than that of pure PTFE under the same conditions (0.22). The lowest wear volume (0.44 mm3) is obtained with PA66/PPS/30 vol % PTFE composite, which decreased by 91% compared with unfilled PA66/PPS blend (4.99 mm3). The topography of transfer film and the elemental distribution were investigated by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS), respectively. Because of the characteristic crystalline structure, PTFE preferentially transferred to the steel ring surface and formed a thin, uniform and firmly adhered transfer layer, which reduced the ability of PA66/PPS blend to transfer and prevent the adhesion between the sample and the couterface. In addition, the superior lubrication of PTFE inhibited the frictional heat melting during sliding. All these aspects are close related to the friction and wear behavior of PA66/PPS/PTFE composite. Upon the addition of PTFE, thermal control of friction regime is not applicable to the PA66/PPS blend. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 969–977, 2006
Co-reporter:Xujun Liu;Zhaobin Chen;Renguo Lü;Tongsheng Li
Journal of Applied Polymer Science 2006 Volume 102(Issue 1) pp:523-529
Publication Date(Web):28 JUL 2006
DOI:10.1002/app.24253
Based on previous work, 70 vol % PA66/30 vol % PPS blend was selected as a matrix, and the PA66/PPS blend reinforced with different content of glass fiber (GF) was prepared in this study. The mechanical properties of PA66/PPS/GF composites were studied, and the tribological behaviors were tested on block-on-ring sliding wear tester. The results showed that 20–30 vol % GF greatly increases the mechanical properties of PA66/PPS blend. When GF content is 20 vol %, the friction coefficient of composite is the lowest (0.35), which is decreased by 47% in comparison with the unfilled blend. The wear volume of the GF-reinforced PA66/PPS blend composite decreases with the increase of GF content. However, the wear-resistance is not apparently improved by the addition of GF in the experimental range for comparison with unfilled PA66/PPS blend. The worn surface and the transfer film on the counterface were examined by scanning electron microscopy (SEM). The observations revealed that the friction coefficient of composite depends on the formation and development of a transfer film. The wear mechanism involves polymer matrix wear and fiber wear. The former consists of melting wear and plastic deformation of the matrix, while the latter includes fiber sliding wear, cracking, rupturing, and pulverizing. The contributions of the matrix wear and the fiber wear determine the ultimate wear volume of PA66/PPS/GF composite. In addition, the abrasive action caused by the ruptured glass fiber is also a very important factor. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 523–529, 2006
Co-reporter:Shi-Quan Lai, Tong-Sheng Li, Xu-Jun Liu, Ren-Guo Lv, Li Yue
Tribology International 2006 Volume 39(Issue 6) pp:541-547
Publication Date(Web):June 2006
DOI:10.1016/j.triboint.2005.03.016
The nano-attapulgite powder was treated by heating at 100, 200, 300, 400, 500, 600, 700 and 800 °C for 2 h in a muffle furnace. PTFE composites were prepared by compression molding PTFE and thermally treated nano-attapulgite. The friction and wear tests were performed on a block-on-ring wear tester. Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectrometer (EDS) and Differential Scanning Calorimetry (DSC) were utilized to investigate material microstructures and examine modes of failure. Experimental results showed that under all experimental conditions there was no significant change in coefficient of friction, but the wear rate of PTFE composites was orders of magnitude less than that of pure PTFE under same experimental conditions. Moreover, thermally treated attapulgite was superior to untreated attapulgite in enhancing the wear resistance of PTFE. In addition, the wear resistance increased monotonically with increasing treated attapulgite concentration. Hardness analysis revealed the hardness of PTFE composites increased with increasing content of treated attapulgite. Investigation of transfer film and analysis of debris for PTFE and its composites showed that thermally treated nano-attapulgite filled to PTFE could facilitate formation of transfer film on the steel ring surface and inhibit breakage of PTFE molecular chain. The composites with higher heat absorption capacity exhibited improved wear resistance. Furthermore, the steel ring counterface abrasion was not found.
Co-reporter:Shi-Quan Lai, Li Yue, Tong-Sheng Li, Zhi-Meng Hu
Wear 2006 Volume 260(4–5) pp:462-468
Publication Date(Web):24 February 2006
DOI:10.1016/j.wear.2005.03.010
The friction and wear properties of polytetrafluoroethylene (PTFE) filled with ultrafine diamond (UFD) were studied in detail on a block-on-ring wear tester under dry sliding conditions. Transmission electron microscope (TEM) was used to research microstructure of the purchased UFD and the purified UFD. Scanning electron microscope (SEM) and differential scanning calorimetry (DSC) were utilized to investigate material microstructures and examine modes of failure. Experimental results showed that there was no significant change in coefficient of friction, but the wear rate of the PTFE composite was orders of magnitude less than that of pure PTFE with increasing purified UFD content. Analysis of SEM indicated UFD in PTFE matrix had effects of loading-carry and increasing formation of transfer films on the steel counterpart surface as well as inhabiting generation of bigger debris. Furthermore, DSC disclosed that the PTFE composite with higher heat absorption capacity exhibited improved wear resistance. Wear mechanism was probably that UFD particles had a function of rolling bearing in frictional interface, and resulted in change of PTFE frictional form from single macromolecular sliding friction to a mixed form of sliding and rolling friction, accordingly UFD in PTFE could obviously decrease wear of pure PTFE.
Co-reporter:Li Yue;Shi-Quan Lai;Xu-Jun Liu;Ren-Guo Lv
Macromolecular Materials and Engineering 2005 Volume 290(Issue 3) pp:195-201
Publication Date(Web):17 MAR 2005
DOI:10.1002/mame.200400336
Summary: PI/AT hybrid materials were prepared by blending of poly(amic acid) and purified AT as a type of fibrillar clays. The friction and wear behaviors of the PI hybrids were evaluated on a ball-on-disc wear tester. The particle size of AT in the hybrid containing 5 wt.-% AT was about 10–100 nm in diameter and 100–1 000 nm in length. Tensile tests on the PI hybrids showed that the strength and the toughness of PI/AT hybrid materials were improved simultaneously when the content of AT was less than 5 wt.-%. The friction coefficient and wear rate of the PI hybrids first decreased and then increased with increasing content of AT. The wear rate of the hybrid containing 3 wt.-% AT was more than 6 times lower than that of pure PI. SEM examination of worn surfaces showed that type of wear changed from adhesive wear of pure PI into abrasive wear of the PI hybrids with adding AT to PI matrix. Debris analysis suggested that AT as filler inside the PI matrix could prevent the formation of bigger debris and a chemical reaction that occurred during the friction process of pure PI but not in the hybrids.
Co-reporter:Ren-Guo Lv;Xu-Jun Liu;Xiao-Xia Liu
Macromolecular Materials and Engineering 2005 Volume 290(Issue 3) pp:172-178
Publication Date(Web):17 MAR 2005
DOI:10.1002/mame.200400213
Summary: Wear behavior correlations with morphology have been established from polytetrafluoroethylene (PTFE) drawn at 200, 327, and 375 °C with draw ratio about 4. The friction coefficient and wear rate for PTFE drawn at 327 °C are lower and the wear rate is lower than that of undrawn PTFE by about 30%. The structures of samples were characterized by scanning electron microscope (SEM), DSC, and wide angle X-ray diffraction (WAXD). Results indicate that the debris morphologies of samples are different. The differences in the tribological behavior of undrawn and drawn samples were attributed to the improvement of the degree of the crystalline, fibrillation, and orderliness by drawing, especially, for PTFE drawn at 327 °C. The orderliness of molecular arrangement along the drawn direction is also higher for PTFE drawn at 327 °C than those of PTFE drawn at 200 and 375 °C, respectively. Therefore, the intensity of covalent bond along drawn direction is higher. The shear resistance and the deformability of the material are greatly improved and the size of the wear breakage unit decreases, which results in a good tribological property for PTFE drawn at 327 °C.
Co-reporter:Tongsheng Li;Zhaobin Chen;Renguo Lü;Xujun Liu
Journal of Polymer Science Part B: Polymer Physics 2005 Volume 43(Issue 18) pp:2514-2523
Publication Date(Web):28 JUL 2005
DOI:10.1002/polb.20548
Polyamide 66 (PA66)/high density polyethylene (HDPE) blends having miscible structure were produced by compatibilization of HDPE grafted with maleic anhydride (HDPE-g-MAH). Mechanical and tribological properties of blends in different compositions were tested. It was found that the polymer blends greatly improved the mechanical properties of PA66 and HDPE. Blending HDPE with PA66 significantly decreased the friction coefficient of PA66; the friction coefficients of blends with different compositions were almost the same and approximately equal to that of pure HDPE; the blends with 80 vol % PA66 exhibited the best wear resistance. The transfer films, counterpart surfaces, and wear debris formed during sliding were investigated by Scanning Electron Microscopy (SEM), and Differential Scanning Calorimetry (DSC) analysis was further carried out on wear debris. These investigations indicated that the thermal control of friction model is applicable to PA66/HDPE blend, that is the friction coefficient of blend is governed by the HDPE component, which possesses a lower softening point relative to the PA66 component in this system. The wear mechanism of PA66/HDPE blend transforms from PA66 to HDPE as the HDPE content increases. PA66, as the component with higher softening point, increases the hardness of blend, enhances the ability of blend to form a transfer film on the counterface, and inhibits the formation of larger belt-like debris of HDPE, at the same time, the presence of self-lubricating HDPE in the system decreases the friction coefficient and the frictional heat, all of these factors are favorable for the wear resistance of PA66/HDPE blend. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2514–2523, 2005
Co-reporter:Zhao-Bin Chen;Yu-Liang Yang;Yu Zhang;Shi-Quan Lai
Macromolecular Materials and Engineering 2004 Volume 289(Issue 7) pp:662-671
Publication Date(Web):29 JUN 2004
DOI:10.1002/mame.200300266
Summary: In this paper, immiscible, partially miscible and miscible blends of polyamide 66 (PA66) and high density polyethylene (HDPE) were obtained by changing compatibilizer concentrations. Mechanical and tribological properties of materials were tested. It was found that the addition of compatibilizer greatly improved the mechanical properties of PA66/HDPE blends. The wear of PA66/HDPE blends was strongly affected by the phase structure. The best blend for lower friction coefficient and higher wear resistance was the blend with a miscible structure, which significantly improved the tribological properties of PA66 and HDPE. SEM investigations on the worn surface and the steel counterface indicated that, for the immiscible and partially miscible blend systems, the dispersed HDPE particles were pulled out from the worn surfaces during sliding because of the poor adhesion between HDPE and PA66, while this was not observed in the miscible blend system.
Co-reporter:Shi-Quan Lai;Xu-Jun Liu;Ren-Guo Lv
Macromolecular Materials and Engineering 2004 Volume 289(Issue 10) pp:916-922
Publication Date(Web):13 OCT 2004
DOI:10.1002/mame.200400140
Summary: A solid lubricant composite material was prepared by compression molding PTFE and acid treated nano-attapulgite. The friction and wear tests were performed on a block-on-ring wear tester. Scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS) and DSC were utilized to investigate material microstructures and examine modes of failure. Experimental results showed that there was no significant change in coefficient of friction, but the wear rate of the PTFE composite was orders of magnitude less than that of pure PTFE. Acid treated nano-attapulgite was superior to untreated nano-attapulgite in enhancing the wear resistance of PTFE. Moreover, the wear resistance of the composite increased monotonically with increasing treated attapulgite concentration. Investigation of transfer film and analysis of debris for PTFE and its composite showed that acid treated nano-attapulgite filled to PTFE could facilitate formation of transfer film on the steel ring surface and inhibit breakage of PTFE molecular chain. The PTFE composite with higher heat absorption capacity exhibited improved wear resistance. Furthermore, the steel ring counterface abrasion was not found.
Co-reporter:Zhaobin Chen, Tongsheng Li, Yuliang Yang, Xujun Liu, Renguo Lv
Wear 2004 Volume 257(7–8) pp:696-707
Publication Date(Web):October 2004
DOI:10.1016/j.wear.2004.03.013
Polymer blending is a very important and widely used method for the modification of polymer materials. The mechanical properties, miscibility and modification mechanisms of blends have been investigated earlier. However, studies of their tribological behavior have been few, and little attention has been paid to the friction and wear mechanisms of polymer blends. In this paper, the structure, mechanical and tribological properties of polyamide 66 (PA66) and polyphenylene sulfide (PPS) blends were studied. It was found that the PA66/PPS blends had a two-phase structure; the blend with 30 vol.% PPS exhibited the best general mechanical properties; 80 vol.% PA66–20 vol.% PPS blend had the lowest wear.Differential scanning calorimetry (DSC) and Fourier transform infrared spectrometry (FT-IR) analyses were carried out and the transfer films on the mating steel surfaces were investigated by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results indicated that the crystalline structure of PA66, PPS and PA66/PPS blends changed due to sliding and tribochemical reactions occurred with the PA66 and the PA66 phases in blends. The thermal control of friction model is applicable to this blend system, i.e. the friction coefficient of PA66/PPS blends depended on the PA66 component with lower melting point, while the wear properties were governed by the adhesive ability between the PPS and the counterface.
![POLY[OXY-1,4-PHENYLENE(1-METHYLETHYLIDENE)-1,4-PHENYLENEOXY(CARBOXYPHENYLENE)CARBONYLIMINO-1,4-PHENYLENEOXY-1,4-PHENYLENEIMINOCARBONYL(CARBOXYPHENYLENE)]](http://img.cochemist.com/ccimg/70600/70563-60-9.png)
![POLY[OXY-1,4-PHENYLENE(1-METHYLETHYLIDENE)-1,4-PHENYLENEOXY(CARBOXYPHENYLENE)CARBONYLIMINO-1,4-PHENYLENEOXY-1,4-PHENYLENEIMINOCARBONYL(CARBOXYPHENYLENE)]](http://img.cochemist.com/ccimg/70600/70563-60-9_b.png)
