Pure Polyoxymethylene Research Articles

Investigation on the mechanical, thermal and electrical properties of polyoxymethylene composites modified by thermoplastic polyurethane elastomer and carbon fiber

As we all know, adding thermoplastic polyurethane elastomer(TPU) into Polyoxymethylene(POM) by melt blending can not only improve its toughness, but also improve the brittleness and cracking of POM products at low temperatures. However, there are some problems in the use of above POM/TPU modified material. For example, after adding TPU, the strength and rigidity of POM resin will be significantly reduced, and its antistatic performance is not very good. In this paper, we use melt-extrusion blending method to improve the strength, rigidity and antistatic properties of toughened POM material by adding CF. In addition, the aggregation and properties of the blends are studied by DSC, FTIR, PLM, DMA and mechanical tests, surface resistivity. Mechanical analysis show us that the tensile strength, flexural modulus increase significantly with the increase of CF content, and the notched impact strength of the POM/TPU/CF materials are all better than that of the pure POM resin. It can also be found that after adding 2% to 8% CF, the surface resistivity of the composites gradually decreases with the increase of CF content, and CF forms a conductive network in the POM matrix. The anti-static test shows that when the CF content is 6% the surface resistivity of POM/TPU/CF blend is 109Ω, and when the CF content is 8% which can reach to 104Ω.

Load-bearing analysis of polymer nanocomposite gears using a temperature-based step loading technique: Experimental and numerical study

The load-bearing characteristic of polyoxymethylene (POM)/carbon black (CB)/CaCO3 ternary nanocomposite gears were assessed using a temperature-based step loading approach. An online temperature measuring system was integrated into the gear test rig to continuously measure the gears’ bulk temperature. Dynamic mechanical thermal analysis (DMTA) was performed to explore a correlation between the viscoelastic characteristics, failure, and wear behavior of nanocomposite gears. The step loading test results showed that the load-bearing capacity was incremented from 7 Nm for pure POM to 10 Nm for POM/CB/3CaCO3 ternary nanocomposite gear. The finite element analysis of gears indicated that the maximum contact stress was different for those with similar critical torque. It was suggested that the maximum contact stress could complement the step loading technique in defining the load-carrying capacity of polymer-based gears. The failure analysis indicated the impediment of tooth cracking and thermal bending in ternary nanocomposite gears. The scanning electron microscopy (SEM) micrographs showed a much smoother tooth worn surface with minor traces of surface cracks and plastic flow for ternary nanocomposites, assigned to the promoted wear resistance, elastic response, and lower hysteretic self-heating due to the synergetic reinforcing effects of CB and nano-CaCO3.

Effect of carbon fiber addition on the tribological properties of polyoxymethylene composites

AbstractThis study focuses on the effect of carbon fibers (CFs) addition on the tribological properties of both polyoxymethylene (POM) and POM/polytetrafluoroethylene (PTFE) blends. Two kinds of CFs with different fiber length (i.e., 40 μm and 1 mm) were compared. Results showed that the addition of longer CFs could effectively reduce the wear rate of pure POM and POM/PTFE composites. Both high P × V friction coefficient and mass wear rate of POM/PTFE particle/CF composites were significantly reduced when compared with the POM/PTFE particle counterparts, which is related to the easier formation of transfer film on the sliding countersurface and better load transfer of CFs. This study provides a new perspective for improving the tribological properties of engineering plastics by tailoring the geometry of functional fillers.

Gear life and failure mode versus meshing stress in polyacetal/carbon black nanocomposite gears

The life and failure mode of polyoxymethylene (POM) and POM/carbon black (CB) spur gears were assessed under different torque levels. A new experimental approach was performed to obtain the transition torque of polymer based gears by employing the online temperature monitoring and step-loading. The gear life versus contact stress was experimentally investigated and a life prediction model was proposed. Dynamic mechanical thermal analysis (DMTA) assessment was employed to determine the viscoelastic behavior of gear materials. The POM/CB gears exhibited improved load capacity, heat performance and service life. The POM/CB gear material demonstrated higher storage modulus and lower hysteresis heating as compared to pure POM gear material. The addition of CB nanoparticles switched the failure mode from fracture to tooth thinning and tooth tip plastic deformation at lower levels of torque (6, 8 and 10 Nm). At higher torque levels (12 and 14 Nm), the POM/CB gears showed 52% and 65.2% increases in the service life, compared to the pure POM gears, and finally failed under thermal material flowing.

Preparation of polyoxymethylene/methyl vinyl silicone rubber/thermoplastic polyurethane ternary thermoplastics vulcanizates with good toughness properties

Novel thermoplastic vulcanizates (TPVs) based on polyoxymethylene (POM) and methyl vinyl silicone rubber (MVQ) have been prepared by dynamic vulcanization process through a batch mixer. During the preparation of TPV blends, Di-(tert butyl peroxyisopropyl) benzene (BIBP) was used as the curing agent in order to make MVQ cross-linked and TPU was used to coat MVQ for improving the compatibility of MVQ and POM. In order to understand the influence of different compositions on TPV blends, five groups of experimental processes were described in detail. During these experiments, the amount of POM was reduced from 70phr to 30phr, that of MVQ was gradually increased from 18phr to 42 phr, and TPU was increased from 12phr to 28phr. In addition, the morphology and properties of TPVs were studied by DSC, FTIR, SEM, DMA and mechanical tests. The mechanical testing results showed that with the amount of POM decreasing and the total amount of MVQ and TPU increasing, the tensile strength of the TPV blends gradually was decreased, and the elongation at break was increased accordingly from 35.2 ± 6% of pure POM to 142.8 ± 11% of sample 5#.

Structure and Properties of Polyoxymethylene/Silver/Maleic Anhydride-Grafted Polyolefin Elastomer Ternary Nanocomposites.

In the present study, silver (Ag) nanoparticles and maleic anhydride-grafted polyolefin elastomer (MAH-g-POE) were used as enhancement additives to improve the performance of the polyoxymethylene (POM) homopolymer. Specifically, the POM/Ag/MAH-g-POE ternary nanocomposites with varying Ag nanoparticles and MAH-g-POE contents were prepared by a melt mixing method. The effects of the additives on the microstructure, thermal stability, crystallization behavior, mechanical properties, and dynamic mechanical thermal properties of the ternary nanocomposites were studied. It was found that the MAH-g-POE played a role in the bridging of the Ag nanoparticles and POM matrix and improved the interfacial adhesion between the Ag nanoparticles and POM matrix, owing to the good compatibility between Ag/MAH-g-POE and the POM matrix. Moreover, it was found that the combined addition of Ag nanoparticles and MAH-g-POE significantly enhanced the thermal stability, crystallization properties, and mechanical properties of the POM/Ag/MAH-g-POE ternary nanocomposites. When the Ag/MAH-g-POE content was 1 wt.%, the tensile strength reached the maximum value of 54.78 MPa. In addition, when the Ag/MAH-g-POE content increased to 15wt.%, the elongation at break reached the maximum value of 64.02%. However, when the Ag/MAH-g-POE content further increased to 20 wt.%, the elongation at break decreased again, which could be attributed to the aggregation of excessive Ag nanoparticles forming local defects in the POM/Ag/MAH-g-POE ternary nanocomposites. Furthermore, when the Ag/MAH-g-POE content was 20 wt.%, the maximum decomposition temperature of POM/Ag/MAH-g-POE ternary nanocomposites was 398.22 °C, which was 71.39 °C higher than that of pure POM. However, compared with POM, the storage modulus of POM/Ag/MAH-g-POE ternary nanocomposites decreased with the Ag/MAH-g-POE content, because the MAH-g-POE elastomer could reduce the rigidity of POM.

Improving the Toughness and Thermal Resistance of Polyoxymethylene/Poly(lactic acid) Blends: Evaluation of Structure-Properties Correlation for Reactive Processing.

The study focuses on the development of polyoxymethylene (POM)/poly(lactic acid) (PLA) blends with increased impact and thermal resistance. The study was conducted in two phases; in the first part, a series of unmodified blends with PLA content of 25, 50, and 75 wt.% was prepared, while the second part focused on the modification of the PLA/POM (50/50) blends. An ethylene/butyl acrylate/glycidyl methacrylate terpolymer (E/BA/GMA) elastomer (EBA) was used to improve the impact strength of the prepared blends, while reactive blending was used to improve interfacial interactions. We used a multifunctional epoxy chain extender (CE) as the compatibilizer. Static tensile tests and notched Izod measurement were used to evaluate the mechanical performance of the prepared samples. The thermomechanical properties were investigated using dynamic mechanical thermal analysis (DMTA) analysis and heat deflection temperature (HDT)/Vicat softening temperature (VST) methods. The crystallinity was measured using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXS) measurements, while the rheology was evaluated using a rotational rheometer. The paper also includes a structure analysis performed using the SEM method. The structural tests show partial miscibility of the POM/PLA systems, resulting in the perfect compatibility of both phases. The impact properties of the final blends modified by the EBA/CE system were found to be similar to pure POM resin, while the E modulus was visibly improved. Favorable changes were also noticeable in the case of the thermomechanical properties. The results of most of the conducted measurements and microscopic observations confirm the high efficiency of the reaction for PLA as well as for the modified POM/PLA mixtures.

Characterization and Properties of Thermoplastic Polyether Elastomer/Polyoxymethylene Blends Prepared by Melt-Mixing Method

Thermoplastic polyester elastomer is a block copolymer comprising polyester hard segments and polyether soft segments. The soft section gives elasticity, making it rubbery; the hard section gives the same processing properties and mechanical strength as engineering plastic has. In this paper, the thermoplastic polyester elastomer/polyoxymethylene composites were prepared by melt extrusion and the content of thermoplastic polyester elastomer in the blends was 5, 10, 15, 20 and 25 wt %, respectively. The compatibility of composites was studied by DSC, FTIR, SEM and DMA. The mechanical tests showed that the notched impact strength and the elongation at break of the blends were significantly better than pure polyoxymethylene.

Synthesis of siloxane‐containing benzoxazine and its synergistic effect on flame retardancy of polyoxymethylene

A type of trialkoxysilane‐containing naphtholoxazine compound (Naph‐boz) was successfully synthesized and combined with ammonium polyphosphate/melamine (APP/ME) as an intumescent flame retardant (IFR) to improve the flame‐retardant efficiency of polyoxymethylene (POM). The Underwriters Laboratories 94 (UL94) vertical burning test, limiting oxygen index (LOI), cone calorimeter, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and Raman spectral analysis were used to study the flame‐retardant properties and related mechanism. The results showed that the formulation with 20 wt.% of APP, 6 wt.% of ME, and 4 wt.% of Naph‐boz passed UL94 V‐1 rating, and the LOI value was improved to 40.3%. Compared with pure POM, the IFR with Naph‐boz had greater reduction in peak heat release rate (lower 74.9%) and total heat release (lower 40.2%). SEM images showed that compact and reinforcing charred layer was formed during the POM/IFR/4Naph‐boz samples combustion, which was beneficial at reducing and maintaining low combustion parameters throughout the cone calorimeter test. The synergistic flame‐retardant effect between Naph‐boz and APP/ME was considered as the reason for the improvement in flame retardancy POM. Furthermore, because of the Naph‐boz was conducive to the compatibility between the flame retardants and matrix, the notched Izod impact strength of POM/IFR/4Naph‐boz composite was higher than that of POM/IFR system.

Spinnability and characteristics of polyoxymethylene-based core–sheath bicomponent fibers

In this work, the spinning abilities of polyoxymethylene-based core–sheath bicomponent fibers were investigated. Bicomponent fibers were prepared using polyoxymethylene as the core material and poly(lactic acid) blended with polyoxymethylene or pure polyoxymethylene as sheath materials, and their characteristics were investigated and compared. Fiber properties such as elongation are important because they directly relate to the spinning performance during fiber processing. This work reports the impact of the composition designation of the core–sheath bicomponent fibers on the controllable stability of poly(lactic acid) in polyoxymethylene–poly(lactic acid) blends in the fibers, as well as the influence of the core–sheath material on the structure, fiber diameter and distribution, thermal stability, and mechanical properties of the core–sheath bicomponent fibers. It was found that the selection of core and sheath materials affected the structural characteristics of the fibers. The polyoxymethylene core–polyoxymethylene sheath (FV) fiber showed dimensional stability. However, the polyoxymethylene core–poly(lactic acid)/polyoxymethylene sheath (FT30) fiber provided the optimum limit of poly(lactic acid) content for controlling the stable properties of the core–sheath bicomponent fibers.

Characterization of composites based on polyoxymethylene and effect of silicone addition on mechanical and tribological behavior

Additives to polymer materials allow to obtain a wide range of functional properties. The improvement of wear and durability of plastics is achieved by the use of powder or fibrous fillers and complex modifications of structure. The aim of the work was to examine the physical, mechanical and tribological properties of modified polyacetal. As a modifiers various types of silicon, thermoplastic polyurethane and aramid fiber were used. The addition of above mentioned additives reduces the coefficient of friction and the wear rate in relation to pure polyoxymethylene, moreover used additives increase the strength properties. Studies have shown that the addition of filler allows to provide excellent tribological properties while maintaining high strength properties. POLYM. ENG. SCI., 59:935–940, 2019. © 2018 Society of Plastics Engineers

Effect of Polyhedral Oligomeric Silsesquioxane on the Melting, Structure, and Mechanical Behavior of Polyoxymethylene.

The effects of octakis[(3-glycidoxypropyl)dimethylsiloxy]octasilsesquioxane (GPOSS) on the crystallinity, crystal structure, morphology, and mechanical properties of polyoxymethylene (POM) and POM/GPOSS composites were investigated. The POM/GPOSS composites with varying concentrations of GPOSS nanoparticles (0.05–0.25 wt %) were prepared via melt blending. The structure of POM/GPOSS composites was characterized by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and polarized light microscopy (PLM). The mechanical properties were determined by standardized tensile tests. The morphology and dispersion of GPOSS nanoparticles in the POM matrix were investigated with scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. It was observed that the dispersion of the GPOSS nanoparticles was uniform. Based on DSC studies, it was found that the melting temperature, lamellar thickness, and the degree of crystallinity of the POM/GPOSS composites increased. The POM/GPOSS composites showed an increased Young’s modulus and tensile strength. Finally, compared with the pure POM, the addition of GPOSS reduced the spherulites’ size and improved the crystallinity of the POM, which demonstrates that the nucleation effect of GPOSS is favorable for the mechanical properties of POM.

Effects of Amino-Functionalized Graphene Oxide on the Mechanical and Thermal Properties of Polyoxymethylene

Polyoxymethylene (POM)/graphene oxide (GO) composites are fabricated using a melt blending method. GO is modified, respectively, by 3-aminopropyltriethoxysilane (KH550-GO) and polyethylenimine (PEI-GO) to enable its uniform distribution in the POM matrix. The mechanical properties of the POM/GO composites are dramatically improved compared to those of pure POM even at a very low loading of GO. The tensile strength and Young’s modulus as well as storage and loss moduli increase by 17.1%, 45.4%, 97.3%, and 94.7%, respectively. The thermal stability of the composites is also greatly promoted. Fourier transform infrared and X-ray photoelectron spectra reveal that the enhanced properties are mainly stemmed from the notable interfacial interactions between the −NH groups in GO sheets and POM chains.

Magnet-Sleeve-Sealed Mini Trochoidal-Gear Pump Prototype with Polymer Composite Gear

The trochoidal-gear technology has been growing in groundbreaking fields. Forthcoming applications are demanding to this technology a step forward in the conceiving stage of positive displacement machines. The compendium of the qualities and the inherent characteristics of trochoidal-gear technology, especially towards the gerotor pump, together with scale/size factor and magnetic-driven transmission has led to the idea of a magnet-sleeve-sealed variable flow mini trochoidal-gear pump. From its original concept, to the last phase of the design development, the proof of concept, this new product will intend to overcome problems such as noise, vibration, maintenance, materials, and dimensions. The paper aims to show the technological path followed from the concept, design, and model, to the manufacture of the first prototype, where the theoretical and numerical approaches are not always directly reflected in the prototype performance results. Early in the design process, from a standard-commercial sintered metal mini trochoidal-gear unit, fundamental characteristics and dimensional limitations have been evaluated becoming the strategic parameters that led to its configuration. The main technical challenge to confront is being sealed with non-exterior driveshaft, ensuring that the whole interior is filled and wetted with working fluid and helping the hydrodynamic film formation, the pumping effect, and the heat dissipation. Subsequently, the mini pump architecture, embodiment, methodology, materials, and manufacture are presented. The trend of applications of polymer composite materials and their benefits wanted to be examined with this new mini pump prototype, and a pure polyoxymethylene mini trochoidal-gear set has been designed and manufactured. Finally, both the sintered and the polymer trochoidal-gear units have been experimentally tested in an in-house full-instrumented mini test bench. Although the main goal of the presented work is the development of a new mini trochoidal-gear pump prototype rather than a numerical study, the results have been compared with numerical simulation. Subsequently, the prototype of the mini trochoidal-gear pump is a feasible proof of concept supported by functional indexes and the experimental results.

Morphology and Properties of Polyoxymethylene/Polypropylene/Microcrystalline Cellulose Composites

The effects of microcrystalline cellulose (MCC) on mechanical, thermal and morphological properties of polyoxymethylene (POM)/polypropylene (PP) blends at different compositions were investigated. The blends and composites were prepared by melt mixing using an internal mixer at 200°C. Scanning electron microscopy (SEM) analysis revealed phase separation between POM and PP phases due to the difference in polarity of POM and PP. When adding the MCC in the blends the morphology slightly changed due to the weak interaction between MCC and polymer phases. Incorporation of MCC at 5 phr could improve Young’s modulus of POM/PP blends. The storage modulus of the blends was improved after adding MCC 5 phr due to reinforcing effect of the MCC. The thermal properties found that the addition of MCC had no effect on the melting temperature of the blends. The blends exhibited higher decomposition temperature than pure POM. The blends showed the decomposition temperatures increased when increasing amount of PP content, which were higher than pure POM. Therefore, it may be inferred that the addition of PP could enhance the thermal stability of the POM/PP blends, but the addition of MCC did not improve the thermal stability.

Polyoxymethylene/ethylene butylacrylate copolymer/ethylene‐methyl acrylate‐glycidyl methacrylate ternary blends

Blends of compatibilized polyoxymethylene (POM)/ethylene butylacrylate copolymer (EBA)/ethylene‐methyl acrylate‐glycidyl methacrylate copolymer (EMA‐GMA) and uncompatibilized POM/EBA were investigated. The notched impact strength of the compatibilized blends was higher than that of their uncompatibilized counterparts. The toughness of the POM blends was improved obviously with relatively low loading of EBA. Fourier transform infrared spectroscopy (FTIR) spectra of EMA‐GMA, pure POM, and POM/EBA/EMA‐GMA blends indicated that epoxy groups of EMA‐GMA reacted with terminal hydroxyl groups of POM molecular chains. The glass‐transition temperature (Tg) values of the POM matrix and the EBA phase were observed shifted to each other in the presence of EMA‐GMA compatibilizer indicating that the compatibilized blends had better compatibility than their uncompatibilized counterparts. With the addition of EBA to POM, both the compatibilized and uncompatibilized blends showed higher onset degradation temperature (Td) than that of pure POM and the Td values of the compatibilized blends were higher than those of their uncompatibilized counterparts. The scanning electron microscopy showed better EBA particles distribution state in the compatibilized system than in the uncompatibilized one. The compatibilized blend with an obvious rougher impact fracture surface indicated the ductile fracture mode. POLYM. ENG. SCI., 58:1127–1134, 2018. © 2017 Society of Plastics Engineers

Mechanical and Tribological Properties of Short Basalt Fiber-reinforced Polyoxymethylene Composites

In this paper, short basalt fiber-reinforced polyoxymethylene (POM) composites were prepared by melt blending and injection molding. The mechanical and tribological properties of the composites were studied by an orthogonal experiment. It was found that the optimal combination of fiber length 4 mm, fiber content 20 wt% and treated with KH550 would result in a comprehensive property which is 27.45% higher tensile strength, 9.65% higher impact strength and 18.11% higher flexural strength with compared to that of pure POM. But its tribological properties would be worse with the addition of the basalt fibers. After incorporating 10 wt% of polytetrafluoroethylene (PTFE) into the composites, the tribological properties of the composites was improved, closed to that of pure POM, with an insignificant decrease to their mechanical properties. Moreover, the morphology of fracture surfaces and worn surfaces evaluated by scanning electron microscopy showed good agreement with the results of the literature.

Improved weld strength of vibration welded polyoxymethylene/multiwalled carbon nanotubes hybrid nanocomposites

In this study, carbon nanotubes reinforced polyoxymethylene with different filler loadings was joined by using linear vibration welding technique. The tensile properties of vibration welded polyoxymethylene nanocomposites with different carbon nanotube contents were studied as functions of filler loading and weld pressure. The results showed that the addition of carbon nanotubes into polyoxymethylene slightly improved the matrix tensile strength and pronounced decreased the ductility of pure polyoxymethylene. Interestingly, the weld strength of the nanocomposites was also higher than the polymer matrix strength even at high weld pressure of 2 MPa. Possible reasons for this high weld strength are discussed based on the morphological investigations. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

The influence of polyoxymethylene molar mass on the oxidative thermal degradation of its nanocomposites with hydroxyapatite

In this paper, the influence of mass-average molar mass (M w) of polyoxymethylene (POM) copolymer on the thermooxidative degradation behavior of its nanocomposites with hydroxyapatite (HAp) is reported. POM copolymers’ thermal stability slightly decreases with a decrease in mass-average molar mass. Thermal stability of POM/HAp nanocomposites is lower in comparison with pure POM, and it gets lower with a decrease in mass-average molar mass of POM copolymer. For POM copolymer with the highest molar mass, thermal stability of POM/HAp nanocomposite was ca. 30 °C lower than for pure POM. To get a more in-depth insight into the decomposition process, kinetic analysis of POM/HAp nanocomposite thermal degradation process was performed using Friedman, Ozawa–Flynn–Wall and multiple nonlinear regression methods. The best fit for pristine T2, T3 and T4 copolymers with different molar mass of 100768, 74727 and 68377 g mol−1, respectively, was obtained for one-stage degradation mechanism with autocatalysis, while for T2/10 % HAp and T3/10 % it was parallel reaction model with autocatalysis (Bna) and phase-boundary reaction models (R3). For T4/10 % HAp, the best approximation was found for R2–Bna–D3 reaction model. From hyphenated TG–MS and TG–FTIR thermoanalytical studies, it was found that the main degradation product for POM/HAp nanocomposites is formaldehyde and the amount of other degradation products is lower in comparison with nonmodified POM copolymers.

Crystallization behavior and toughening mechanism of poly(ethylene oxide) in polyoxymethylene/poly(ethylene oxide) crystalline/crystalline blends

In this study, the unique crystallization behavior of poly(ethylene oxide) (PEO) in polyoxymethylene (POM)/PEO crystalline/crystalline blends was examined in detail. This study was the first to report the typical fractionated crystallization of PEO in POM/PEO blends when PEO is fewer than 30 wt.%. The delayed crystallization temperature of PEO was confirmed at about 5°C to 14°C by using differential scanning calorimetry and perturbation–correlation moving‐window 2D correlation IR spectroscopy. Wide‐angle X‐ray diffraction indicates that no new crystal structures or co‐crystals were generated in POM/PEO. The statistical calculations of scanning electron microscopy photos show that the average diameter of PEO particles is 0.227 µm to 1.235 µm and that the number of small particles is as many as 109 magnitudes per cm3. Theory analysis establishes that the delayed crystallization of PEO is a heterogeneous nucleation process and not a homogeneous nucleation process. A significant toughening effect of PEO to POM was also observed. The impact strength of POM/PEO acquires a maximum of 10.5 kJ/m2 when PEO content is 5%. The impact strength of the blend increases by 78.0% compared with pure POM. To improve the toughening effect, the best particle size is established between 0.352 and 0.718 µm, with a PEO particle spacing of 0.351 µm to 0.323 µm. The number of corresponding particles was 0.887 × 109 per cm3 to 3.240 × 109 per cm3. A PEO toughening model for POM was proposed to provide a new and effective way to solve the problem of POM toughening. Copyright © 2014 John Wiley & Sons, Ltd.