POM Matrix Research Articles

The effect of functionalized hydroxyapatite on the thermal degradation behaviour and flammability of polyoxymethylene copolymer

In this work, the effect of functionalized hydroxyapatite (HAp-g-PEG) on the thermal degradation behaviour and flammability of polyoxymethylene copolymer (POM_C) was investigated. Organic–inorganic hybrid additive, obtained by grafting of poly(ethylene glycol) on HAp surface using 1,6-hexamethylene diisocyanate as a linker, has been incorporated into POM matrix through an extrusion process. TG analyses show that the incorporation of HAp-g-PEG into POM_C leads to the significant improvement in the thermal stability of the polymer matrix. This is an important finding as POM, being an engineering polymer, suffers from a relatively low thermal stability that limits processing options to develop advanced composite materials. Based on TG results kinetic parameters of the thermal degradation process using Friedman isoconversional method and nonlinear regression method have been calculated; an increase in activation energy of POM degradation process after incorporation of HAp-g-PEG has been found. Thermoanalytical analyses (TG-FTIR/MS) show that incorporation of HAp-g-PEG has no significant effect on the composition of the thermal degradation products. Flammability investigations showed small effect of HAp-g-PEG 600 on the burning time and rate, however, there was a significant reduction in the amount of dripping during the material’s burning process.

Failure analysis of POM ternary nanocomposites for gear applications: Experimental and finite element study

The main purpose of the present study is to assess the failure behavior of polyoxymethylene/carbon black/CaCO3 ternary nanocomposite gears by employing an experimental gear test setup and a gear renewal technique. The failure-related factors including surface temperature, tooth wear, and failure analysis at macro- and micro-scales were studied. The tooth surface temperature was measured continuously based on an online-measuring approach. The tooth wear was calculated using microscopic images and software analysis. The maximum contact stress on meshing teeth surfaces was specified by finite element analysis. According to SEM micrographs, the application of both nanostructures contributed to a more uniform distribution of each nanophase within the POM matrix. The gear test results indicated an enhanced tooth resistance and service life of up to 58% and 125%, respectively, for ternary nanocomposites relative to neat POM gears. The tooth surface temperature was reduced for nanocomposite gears due to the promoted heat transfer and thermal stability. The tooth deformation and cracking were highly suppressed for ternary nanocomposite gears at failure. The evaluation of teeth surface damages at micro-scale revealed the suppression of plastic flow and material adhesion for ternary nanocomposites.

Characterizations and Properties of POM Toughened by Thermoplastic Polyamide Elastomer

In this work, we investigated the morphology, crystallization, and mechanical properties of the polyoxymethylene/thermoplastic polyamide elastomer (POM/TPAE) blends. It was found that POM and TPAE are partially compatible. By blending with TPAE, the toughness and low-temperature performance of POM can be improved significantly. However, there is a maximum value for the improvement of POM toughness, which is related to the amount of TPAE. We found that TPAE is dispersed in the POM matrix as spherical particles, and the particle size of these varies with the content of TPAE. Another interesting finding is that adding TPAE can change the crystalline properties of POM. For example, after adding TPAE, the crystallization particles of POM become smaller, part of the crystal area disappears, and the crystallization temperature decreases. All these results suggest that TPAE improves the toughness and low-temperature performance of POM by improving the crystallization, morphological structure, and morphology of the POM blends.

Dielectric relaxation mechanisms in polyoxymethylene/polyurethane/layered silicates hybrid nanocomposites

Polyoxymethylene/Polyurethane/Layered Silicates (POM/PU/LS) ternary hybrid nanocomposites were prepared by two methods: (a) direct melt compounding (DM) and (b) melt compounding using a latex-mediated masterbatch (MB) technique. The morphology of the produced specimens and the quality of the dispersion of LS (synthetic sodium fluorohectorite) were examined via Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Broadband dielectric spectroscopy (BDS) was employed in order to study the dielectric response of the two systems in a wide frequency and temperature range. Rich dielectric spectra are recorded, since dielectric relaxation mechanisms originate from POM matrix, PU latex as well as from interfacial phenomena between electrically heterogeneous components of the nanocomposite. Six different mechanisms contribute to the recorded spectra of the examined nanocomposites which are denoted, in terms of decreasing temperature at constant frequency, as Maxwell-Wagner-Sillars (MWS) effect merged with contribution from the DC conductivity, α-mode of POM, α-mode of PU, γ- and δ-modes of POM and γ-mode of PU. The dynamics of the recorded processes as well as the effect of the preparation technique, on the way these processes are imprinted in the dielectric spectra of the examined systems, are considered and discussed.

Tribological behavior and morphology of PTFE particulate-reinforced POM matrix composites

Abstract The friction and wear properties of polyoxymethylene/polytetrafluoroethylene (POM/PTFE) composites were investigated by using a block-on-ring friction tester and special focus was paid to the effect of weight average molar mass (M w ) of POM. To study the thermodynamic characteristics and wear mechanism of composites, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were used. Results showed that friction and wear properties of the composite blends were strongly affected by the M w of POM and the loading fractions of PTFE. POM/PTFE composites with lower M w of POM owned better wear resistance abilities under a high-speed sliding regime, which resulted from the effective lubrication of transferred wear debris under a relatively high sliding speed. However, the transfer layer on the counterface could be easily peeled off under the low sliding speed, resulting in higher wear rate of POM/PTFE composites with lower M w of POM. POM and its composites with high M w showed comparative high friction levels, related to the strong adhesion between the resin and the steel counterpart. DSC analysis showed that POM with lower M w had higher crystallinity, which was beneficial to the improvement of wear resistance in a high-speed sliding condition.

TPU Inclusion Complex Modified POM: Fabrication of High Performance POM Composites with Both Excellent Stiffness–Toughness Balance and Thermostability

The inclusion complex of thermoplastic polyurethane (TPU) and β-cyclodextrins (β-CD) with high TPU contents has been synthesized. The channel structure with large amount of uncovered TPU was confirmed by wide-angle X-ray diffraction (WAXD). High performance poly(oxymethylene) (POM) alloys were fabricated by simply melt mixing neat POM with the synthesized TPU inclusion complex (IC-TPU). The effects of the incorporation of IC-TPU on the structure and properties of POM have been investigated. Scanning electron microscope (SEM) results showed that IC-TPU was dispersed uniformly in POM matrix and there was robust interface between IC-TPU and POM matrix. Tensile test results indicated significant improvement in both strength and ductility of the IC-TPU modified POM as compared with neat POM. Moreover, the incorporation of IC-TPU resulted in the drastically enhanced thermal stability of POM. The initial degradation temperature increased as high as 40 °C with the addition of a small amount of IC-TPU. The investi...

Ocena primernosti bukove žagovine kot ojačitvene komponente pri pripravi termoplastičnih biokompozitov

Beech sawdust was used as reinforcing component for the preparation of biocomposites with polyoxymethylene % POM and polylactic acid % PLA as polymer matrix. Materials with different portions of sawdust, e.g. 5, 10 and 15 wt. %, were prepared by using extrusion and injection techniques. Their mechanical (E modulus, flexural and tensile strength and strain) as well as thermal (melting point, glass transition) properties were determined. The results indicate that sawdust acts as reinforcement of the composites in the case of flexural stress and also tensile strength by POM matrix. Addition of sawdust to POM and PLA increases maximal temperature of biocomposite utilization. The main advantage of new materials is low density. Despite their brittleness they are convenient, low-cost alternatives to composites reinforced with glass fibres.

Miscible crystalline/crystalline polymer blends of polyoxymethylene copolymer/poly(ethylene oxide) with interpenetrated spherulites and enhanced properties

Miscibility and crystallization behavior of a polymer blend consisting of two crystalline components, polyoxymethylene copolymer (Co‐POM) and poly(ethylene oxide) (PEO), have been investigated. Experimental results indicate that Co‐POM is thermodynamically miscible with PEO, as shown by the existence of single‐composition dependent glass transition temperature over the entire composition range. The crystal structures and spherulitic morphologies of (Co‐POM)/PEO blends were studied by X‐ray diffraction, differential scanning calorimetry, scanning electron microscopy, and polarizing light microscopy. It was found that the PEO spherulites crystallized within the matrix of the crystals of the pre‐existing Co‐POM phase and resulted in a high extent of interfibrillar segregation. The unique interpenetrated crystalline structure was beneficial for the sufficient contact between the two components and significantly improved both the toughing and the lubricating effect of PEO on the POM matrix. On incorporation of 30 wt% PEO, the notched impact strength of POM was enhanced from 6.7 to 10.3 MPa, by about 53.7%, while the elongation at break increased from 28.5% to 121.0%, by about 3.2 times. Furthermore, the friction coefficient drastically decreased from 0.35 to 0.17, demonstrating the enhanced tribological performance of the miscible blends. J. VINYL ADDIT. TECHNOL., 22:479–486, 2016. © 2015 Society of Plastics Engineers

Contact stress analysis for a pair of aluminum matrix composite helical gear and steel worm

This paper presents a contact stress analysis for a pair of aluminum matrix composite helical gear and steel worm during rotation. The material of helical gear is 10% SiC particulate-reinforced Al matrix composite. Contact stress analysis for helical gear and worm are performed at different contact positions during rotation based on finite element analysis. Three different conditions are designed to investigate the contact stress of 40Cr, POM and aluminum matrix composite helical gear mesh with worm. Through contrast contact stress between different material helical gear, it was found that the load performance of aluminum matrix composite helical gear is close to steel and better than plastic gear.

The crystallization morphology evolution of polyoxymethylene/poly(ethylene oxide) blend micropart prepared under microinjection molding conditions

ABSTRACTThis article is the first study on the microinjection molding and the effects of the microprocessing parameters on the crystallization and orientation of polyoxymethylene/poly(ethylene oxide) (POM/PEO) blend, which has better toughness and self‐lubricity compared with the neat POM and therefore is a better candidate material for making microparts like microgears with higher performances. The crystalline and phase morphologies were investigated by polarized light microscope (PLM), differential scanning calorimeter (DSC) and scanning electron microscope (SEM). The crystalline orientation of the microparts was evaluated by two‐dimensional wide‐angle X‐ray diffraction (2D‐WAXD) and Herman's orientation function. The experimental results showed that both POM and POM/PEO microparts prepared by microinjection molding exhibited three distinct layers, i.e., skin layer, shear layer and core layer, while the latter had thicker shear layer but thinner skin layer and core layer. PEO was well dispersed in POM matrix. The spherulite size, the melting point as well as the crystallinity of POM in the POM/PEO blend decreased due to the interference of PEO in the crystallization of POM. A shish‐kebab structure was observed in the shear layers of the POM/PEO microparts. The effects of processing parameters on the thicknesses of different layers of the POM/PEO microparts were investigated. With increase of the injection speed or decrease of the mold temperature, the skin layer and the core layer became thicker, while the shear layer and the oriented region became thinner. However, the influence of the injection pressure was not obvious. Also, the processing parameters affected the crystalline orientation of the POM/PEO microparts. With increase of the injection speed or decrease of the mold temperature, the orientation function f decreased, indicating a lower degree of orientation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40538.

The Effects of Interphase and Interface Characteristics on the Tensile Behaviour of POM/CaCO3 Nanocomposites

The condition of the interfacial area and interphase region in a nanocomposite can significantly affect its mechanical performance. In this research, the tensile performance of a POM/CaCO3 nanocomposite, including the modulus of elasticity and tensile strength, are analysed using different mathematical models and the Ansys FEM software. The mechanisms of the plastic deformation and crazing of the POM/CaCO3 nanocomposite were investigated using FEM. Furthermore, the effects of interface adhesion and the interphase property on interfacial debonding, as well as tensile properties, were analysed. The tensile strength of the nanocomposite could not be greater than that of bulk POM because of the failure which was initiated from the matrix. By stiffening the interphase and increasing the adhesion between nanoparticle and polymer, the nanocomposite's elastic modulus and strength were increased. Two toughening mechanisms, including plastic deformation and crack initiation, were observed in the POM/CaCO3 nanocomposite. The high interfacial adhesion of the matrix to the particles led to the formation and propagation of crazes along the extension load in the POM matrix. The tensile strengths of different nanocomposites were over-predicted by the Pukanszky model, while the moduli magnitudes estimated by the Ji mathematical model were less when compared to those determined by FEM.

Structure and mechanical properties of polyoxymethylene/multi-walled carbon nanotube composites

Toughened and reinforced POM/MWCNT composites were prepared by compounding POM with MWCNTs at low filler content. The mechanical strength and toughness of the composites were enhanced at 1 wt% MWCNT loading. The fractured surface of the composite at this loading was very rough, and a certain toughness feature was presented. MWCNTs showed an obvious nucleation effect on POM, leading to an increase of crystallization temperature and crystallization rate, and a reduction of spherulite size. The storage and loss modulus of the composites both increased at all temperatures by introducing rigid MWCNTs, indicating an improved stiffness of composites and strong entanglement between POM and MWCNTs. Under shear stress, MWCNTs were pulled-out with a skin-core structure. The failure mode of the composite was supposed to be the deformation and destruction of POM matrix around the interfacial layer under load.

EFFECT OF INJECTION TEMPERATURE ON DISPERSION PHASES AND MECHANICAL PROPERTIES OF POM/TPU BLENDS

The effects of injection temperature on the dispersion phase and mechanical properties of polyoxymethylene/thermoplastic polyurethane elaster(POM/TPU) blends were investigated.The experimental results showed that the notched impact strength of POM/TPU blends was greatly influenced by injection temperatures,and the highest value,19.1 kJ/m~2,appeared at 195℃,two times as high as the value obtained at 175℃.Because the viscosity ratio of POM to TPU changed with temperature,and reached 1 at around 195℃,and TPU formed strips-like structure in POM matrix along with the flow direction of the melt during injection,which could effectively absorb impact energy,prevent growth of crazes and formation of cracks.With increase of injection temperature,the average particle size of TPU decreased,and the particle size distribution became narrower.It is an effective way to toughen POM by adjusting the viscosity ratio of the dispersion phase and the matrix and controlling the morphology of the dispersion phase.

Assessment of Zn bioavailability: XAFS study on speciation of zinc-particulate organic matter associations in polluted soils

We present a study about the behavior of Zn in agricultural soils polluted 100–50 years ago by metallurgical fallout and used nowadays for corn production. Such type of soil concerns an area of several km2 around former metallurgical complex in Northern France. Despite the moderated metal amounts of these soils, the metals deposited over the agricultural area still indirectly expose nowadays populations through the food chain. In contrast to the most contaminated industrial site, these more distant agricultural areas have been less studied. The study was focused on Zn, a relative mobile metal element, since its predominant occurrence in the surface horizon of sandy textured soils, fifty years after cessation of metallurgical activity suggests its immobilization due to specific soil mechanisms. To evaluate how Zn is associated to POM, Zn K-edge XAFS spectra were collected at 293 K at the SLS on beamlines superXAS and microXAS, using Si(111) monochromators and solid state Ge detectors. Energetic resolution is ca. 2 eV at 9 KeV. Lateral resolution varied from ca. 1 mm2 to 15 micron2. Spectra were normalized with the XAFS 3.0 software. We studied different POM size fractions isolated from soils. The largest POM particles correspond to recent leaves or roots fragments. The finest POM particles correspond to decomposition by-products. The results revealed a multiple and heterogeneous speciation of Zn with POM. We observed that little interactions from next-nearest neighbors around Zn. We concluded that most of the Zn tends to be located in the POM matrix as a Zn-organic speciation. We also collected macroscopic EXAFS data on selected intact POM particles probed at the micron scale. The results show that the remaining Zn-distribution related to inorganic (hot-spots), possibly franklinite-type, is minor compared to the Zn-organic speciation. Such observations will help to better understand the mechanisms that regulate the bioavailability and immobilization of Zn in polluted soils.

Synthesis of the melamine–formaldehyde polycondensate and its thermal stabilization effect on polyoxymethylene

Melamine (MA) was polymeric modified by condensation reacting with formaldehyde (FA) to form the melamine formaldehyde polycondensate (abbreviation: MF) with high molecule-weight and comparatively high processing thermo-stability. The effect of the reacting molar ratio of MA and FA, and the types and concentrations of the dispersion agents on the structure and properties of MF were discussed, and the finely divided, cross-linked, and thermo-stable MF polycondensates were obtained. The thermal stabilization effect of MF on POM was studied by the isothermal weight loss analysis at 220 °C, isothermal weight loss rate analysis at 222 °C, thermal gravity analysis (TGA) and balance torque analysis, which showed that MF has almost the equal thermal stabilization on POM to MA. The multiple processing and long-term thermal stability at high temperature measurements indicated that MF showed even higher thermal stabilization on POM than MA. Moreover, the impact strength was improved after five times of extrusion, due to the better dispersion of MF in POM matrix and better nucleation effect of MF on POM.

ポリアセタール／ポリエチレン（ＬＤＰＥ，ＨＤＰＥ，ＨＭＷＨＤＰＥ）ブレンドのトライボロジー特性

To improve tribological properties of polyacetal (POM), blends with polyethylene (PE) were prepared by extrusion and studied. Three types of PE, i.e., low density polyethylene (LDPE), high density polyethylene (HDPE), and high molecular weight high density polyethylene (HMWHDPE) were employed in the present study. Each specimens in the shape of a pipe containing one of these PE types were rubbed against a rotating carbon steel (S45C) slider under unlubricated conditions. Observation with an electron probe X-ray microanalyzer (EPMA) revealed that the specimens had sea-island structures in which polyethylene particles were finely dispersed in the POM matrix. An optical microscope observation indicated that these polyethylene particles mainly bore the load applied to the frictional surface. The wear volume in both the case where LDPE was blended and that where HDPE was blended showed a remarkable decrease, the blending effect of HDPE being much greater than that of LDPE. The coefficient of friction in both of these cases became smaller, the values indicated becoming nearly the same. On the other hand, contrary to expectations, blending with HMWHDPE resulted tribological properties which were handly improved.

Effect of single screw extrusion through a round die on the morphology of POM/PP blends

POM/PP blends of different compositions were extruded through a round die of 2 mm diameter using a single screw extruder. The morphology of the extrudates was studied using a polarized light microscope (PLM), a scanning electron microscope (SEM) and the solvent extraction technique. A cable-like structure was observed in the extrudates, consisting of circular cords surrounded by a skin layer. The number and distribution of the cords matched with the holes on the breaker plate just before the die. The composition and morphology of the cords were found to vary with the POM/PP composition ratio. For composition ratios between 10/90 and 40/60, the outer cords were rich in PP and only a small amount of POM fibres, particles or thin films were found. In contrast the inner cords contained more POM fibres and they were distributed more evenly within the PP matrix. In the 50/50 blend, both POM and PP fibres were present. In blends with more than 50% POM, the cords were made up of PP fibres in a continuous POM matrix. Cryogenically-fractured sections of the extrudates showed clean fibre/matrix interfaces under the SEM, this being a sign of poor adhesion between the polymers.

Properties of copolymer‐type polyacetal/ethylene–propylene–diene terpolymer blends

AbstractTwo kinds of polymer blends, polyacetals (POMs) and ethylene–propylene–diene terpolymer (EPDM), have been prepared by mechanical blending. The rubbery EPDM was added to the rigid POM matrix to increase toughness. The mechanical, physical, thermal, dynamic mechanical, and morphological properties of these samples have been measured. The notched Izod impact strength and the elongation of the blends reaches a maximum at 7.5 wt % EPDM content. Scanning electron micrographs (SEM) showed that the domain sizes of EPDM vary from 0.25 to 1.0 μm and were independent of the composition. The POM/EPDM blends were determined to be immiscible by SEM, but showed single Tg behavior as determined by differential scanning calorimetry (DSC) and dynamic mechanical analyses up to 7.5 wt % EPDM. Because of that, the Tg's of POM and EPDM were very similar in value. © 1993 John Wiley & Sons, Inc.

The effect of the soft segment of polyurethane on copolymer‐type polyacetal/polyurethane blends

AbstractMechanical blends of copolymer‐type polyacetal (POM) with ester‐based and ether‐based polyurethane (PU) are immiscible over the 0–50% PU compositional range. The PU elastomer was added to the rigid POM matrix to increase its toughness. The mechanical, physical, thermal, dielectric, and dynamic mechanical properties and morphology of POM/PU blends were investigated. The notched Izod‐impact strength of blends reaches a maximum at 10 wt % PU. The tensile strength, Young's modulus, volume resistivity, crystallinity, and density decrease with increasing concentration of PU. The elongation of blends reaches a maximum at 20 wt % PU. The dielectric constant and dissipation factor increase with increasing PU content. From dynamic mechanical measurements, as the elastomer content increases, the height of the damping peak also increases, but there is no transition temperature shift. SEM shows that the blends exhibit a continuous morphology with domain size varying from 1 to 10 μm for PU. However, at a concentration of 50 wt % PU, the dispersed PU particles tend to aggregate. Characterization of morphology by a metallurgical microscope has shown that the crystalline materials in the pure POM and the blends exist in a spherulitic superstructure.