No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Thermoplastic polyurethane toughened polyacetal blends
Abstract
Polyacetal/thermoplastic polyurethane blends at four different polyacetal wt% of 90, 80, 70 and 60 were made using a twin screw extruder. Mechanical, morphological and rheological properties of these blends were determined. The addition of thermoplastic polyurethane (TPU) to polyacetal produces a decrease of tensile and flexural strength of the blend material as the TPU wt% increases. The notched impact strength increases with the increase of TPU wt% in the blends. Scanning electron micrographs of impact fractured surfaces of these blends show droplet dispersion morphology. The melt flow curves for these blends show lower melt viscosity than those of feedstocks in the major range of experimental shear rates. The instrumented impact strength of these blends at 30wt% TPU level are nearly nine times higher than that of polyacetal, and blends at 30 and 40wt% TPU levels failed in a ductile manner, whereas the polyacetal failed in a brittle manner.
... It is pointed out that a small amount of a rubber-like substance such as TPU or ABS particles in the rigid polymeric matrix can greatly improve the crack and impact resistance of normally brittle plastic. The rubber-like particles dispersed in the matrix act as a stress concentrator, forming a barrier to the extension of crazing and stop craze growth [7][8][9][10][11][12]. Thermoplastic Polyurethanes (TPUs) are segmented polymers composed of hard and soft segments forming two-phase microstructure which contains flexible coiled and rigid hard segments, which can be melt down without degradation of the urethane bonds [13][14][15]. ...
... copy. Increasing in toughening, notch impact strength and abrasion resistance of POM by TPU up to 30 percent were also reported in the literatures [8,17,18]. Kumar et al. [19] showed that POM/TPU have more tendency to creep rather than POM and the tendency to creep increases as the TPU content increases. Reduction in crystallinity and subsequently less notch-sensitivity of POM by adding TPU is another observation reported in some studies [7,10]. ...
... The ABS/POM blend shows typical Matrix-Droplet morphology, in which POM domains are dispersed in the ABS matrix. As seen in Fig. 1a, after fracture, some part of the disperse phase has pulled away from the matrix and that portion is still remaining on the fractured surface leaving convex and concave cavities with smooth surface fracture which can be due to poor interfacial adhesion between the ABS and POM [8,20]. By introducing TPU into the blend, dispersion of POM domains improves and the droplet size D n ; reducing from 3.12 to 2.18 m. ...
The effect of thermoplastic polyurethane (TPU) on morphological and rheological properties of polyacetal/acrylonitrile-butadiene-styrene (POM/ABS) blends has been investigated. The morphological investigations revealed that addition of TPU to the blends improves the dispersion of dispersed phase, regardless of the dominant phase. In the POM rich phase blend, this effect was more significant and morphology changed from non-uniform to droplet-matrix. The rheological studies showed that complex viscosity as well as elasticity, increased by adding TPU to the POM/ABS blends. This improvement in rheological properties was more significant in the POM rich phase blend, which was proved by positively deviating blends (PDB) in the complex viscosity curve in the entire range of frequency obtained from the log-additivity rule. Such a phenomenon could have occurred due to partial miscibility of TPU with POM and placement of TPU at the interface and/or in POM phase. Transmission electron microscopy (TEM) micrographs showed that addition of Cloisite 30B nanoclay into the blend creates both intercalated and tactoids morphology. X-ray powder diffraction (XRD) analysis also confirmed the presence of two different types of nanoclay dispersion. TEM results also demonstrated that nanoclay particles morphology was intercalated and was located in the ABS phase as well as phase interfaces.
... To improve the impact toughness of POM and extend its application range, considerable efforts have been made on the toughening of POM. [4][5][6][7][8] Among the elastomers used, thermoplastic polyurethane (TPU) is so far the best toughening agent and can simultaneously enhance both the elongation and thermal stability of POM due to its good compatibility with POM, [8][9][10][11][12][13][14] which is attributed to the possible formation of hydrogen bond between part of POM ether bonds and TPU. 10 The impact strength of POM/TPU blends can be significantly improved with higher addition of TPU (content over 30 wt %), and the toughening mechanism is explained as the formation of a cocontinuous morphology at high TPU addition. 11 In order to further improve the compatibility of POM/TPU, effective compatibilizers were added to enhance the interfacial interactions between POM and TPU. ...
... The investigations of POM/TPU system have mainly focused on the influence of TPU content on mechanical properties, the selection of compatibilizer, interfacial reaction, as well as rheological properties. [9][10][11][12][13][14][15]22 This article reports our endeavor in developing toughened POM/TPU blends with the chain extender, Joncryl ADR-4368. Its efficacy in toughening POM/TPU blends was evaluated in reference to MDI, EPDM-g-MAH and poly(ethylene-octene) grafted with maleic anhydride (POE-g-MAH). ...
Novel compatibilized polyoxymethylene/thermoplastic polyurethane (POM/TPU) blends are successfully developed using multifunctional chain extender, Joncryl ADR‐4368, as the compatibilizer. The outstanding compatibilization efficiency of Joncryl on POM/TPU blend was demonstrated by its even higher mechanical properties with only 0.5 wt % of Joncryl than those with 5 wt % of three commonly used compatibilizers. Addition of only 0.5 wt % Joncryl can double the impact strength and significantly improve its tensile strength and flexural strength for POM/TPU (75/25) blend. SEM images show that Joncryl can reduce TPU particle size and enhance the interfacial interactions between POM and TPU. The interparticle distance of TPU in POM/TPU/Joncryl blends was calculated as 0.2 μm, quite close to the critical matrix ligament thickness of POM/TPU blends (0.18 μm). The impact force profile vividly shows that the addition of Joncyl in POM/TPU blends can dramatically increase the total impact energy absorbed by this blend system and enhance the interfacial interactions between POM and TPU. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
... Thermoplastic polyurethane (TPU), a toughening agent with excellent properties, has been widely used to toughen plastics like PP [27], poly(butylene terephthalate) [28], polylactic acid (PLA) [29,30], poly(methyl methacrylate) [31], and especially polyoxymethylene (POM) [32][33][34][35][36][37][38][39][40]. TPU has been proved to be an effective toughening agent to POM as ether oxygen from POM and urethane group from TPU can form hydrogen bonding to enhance the interfacial adhesion between POM matrix and TPU particles [41]. ...
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
... Generally, the incorporation of TPU as an impact modifier in a thermoplastic matrix improves the impact toughness if proper adhesion between TPU and host phase established. However, this could reduce other mechanical properties of blend comprising tensile and flexural properties [24][25][26]. As reported in previous researches, the incorporation of nanoscale reinforcements in polymeric matrices improved mechanical properties. ...
Thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were incorporated into polyamide 6 in an attempt to enhance notched impact resistance and damping performance. The morphology, mechanical, thermal and viscoelastic properties of different samples were studied. Scanning electron microscopy study indicated a uniform distribution of fine TPU droplets in PA6/TPU blend. Furthermore, well-dispersed CNTs in PA6/TPU matrix and good adhesion of polymer matrix to CNTs were observed. The addition of TPU into PA6 developed a rough fracture surface morphology and increased the notched impact strength equal to 39%, yet declined tensile and flexural resistance. The inclusion of CNTs into PA6/TPU improved mechanical properties comprising tensile, flexural and notched impact strengths as high as 14%, 12% and 16% respectively. The results of dynamic mechanical thermal analysis (DMTA) indicate: the addition of TPU into PA6 improves damping performance; the inclusion of carbon nanotubes in PA6/TPU enhances both energy storage and glass transition temperature.
... Blends are convenient engineering materials because they possess the advantages of each component. The degree of compatibility is a factor that determines the final properties of the blend, and other factors include chemical composition, molecular weight, and catalysts [22,23]. A compatible polymer blend exhibits mechanical properties proportional to the ratio of the constituents of the blend [24]. ...
The possibility of exchange reactions and thermal self-healing in blends of thermoplastic polyurethane (TPU) and phenoxy resin was investigated herein. The analyses were based on characterization obtained via differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), and tensile test. A new phenoxy resin was synthesized from eugenol, and blends with different types of TPU were prepared to investigate the exchange reaction, thermal self-healing, and mechanical properties. The influence of phenoxy resin content on the mechanical behavior and healing efficiency was studied. Improvement of storage modulus owing to the increase of phenoxy resin content was observed. Results suggest that the exchange reaction between phenoxy- and ester-type TPU occurred during thermal treatment. However, little exchange occurred between phenoxy resin and ether-type TPU. Specifically, only ester-type TPU exhibited a significant exchange reaction in the phenoxy resin blend. Furthermore, in the presence of a catalyst (e.g., zinc acetate), the exchange reaction readily occurred, and the healing efficiency improved by the addition of the catalyst and increase in the phenoxy content.
... [15][16][17]. Several works have been reported that TPU can be used as flexibilizer in many brittle polymers, such as polypropylene [18], poly(lactic acid) [19,20], polyacetal [21], poly(butylene terephthalate) [22] and so on. ...
The blends of Poly(propylene carbonate) (PPC) and polyester-based thermoplastic polyurethane (TPU) were melt compounded in an internal mixer. The compatibility, thermal behaviors, mechanical properties and toughening mechanism of the blends were investigated using Fourier transform infrared spectra (FTIR), tensile tests, impact tests, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and dynamic mechanical analysis technologies. FTIR and SEM examination reveal strong interfacial adhesion between PPC matrix and suspended TPU particles. Dynamic mechanical analyzer (DMA) characterize the glass transition temperature, secondary motion and low temperature properties. By the incorporation of TPU, the thermal stabilities are greatly enhanced and the mechanical properties are obviously improved for the PPC/TPU blends. Moreover, PPC/TPU blends exhibit a brittle-ductile transition with the addition of 20 wt % TPU. It is considered that the enhanced toughness results in the shear yielding occurred in both PPC matrix and TPU particles of the blends.
... Both mechanisms could be more or less responsible for improving the impact strength. 29,32 Moreover, as depicted in Figure 1(b) to (d), TPU has good compatibility with PBT because no obvious phase separation is observed and minor phase is not easily distinguishable. The good compatibility between two polymers may be attributed to the lower viscosity of minor phase as compared to major phase. ...
This research studies the properties of poly (butylene terephthalate) (PBT)-based systems toughened with thermoplastic polyurethane (TPU; 10, 20, and 30 wt%) and reinforced with multiwalled carbon nanotubes (CNTs; 0.1, 0.2, and 0.3 wt%). Different compositions prepared via melt mixing. Morphology studies showed good compatibility between the two polymeric phases in PBT/TPU. The addition of TPU to PBT reduced crystallization rate and melt temperature, while inclusion of CNTs had nucleation effect and increased the degree of crystallinity, crystallization, and melt temperatures. The existence of TPU in PBT caused significant enhancement in notch-impact resistant. The inclusion of CNTs to PBT/TPU blend led to the substantial improvements in tensile and flexural strengths and moduli. Dynamic mechanical thermal analysis revealed that the incorporation of CNTs into PBT/TPU enhanced storage modulus and heightened glass transition temperature. The storage modulus of PBT/TPU/CNT nanocomposite containing 0.5 wt% CNT was comparable with that of pure PBT particularly at high temperatures.
... 5 Many studies have reported the melt compounding of POM with flexible polymers such as rubber. 5,[24][25][26][27] However, a blend of PPC and POM has not been studied and it is believed that these resins are able to complement each other in such way that enhanced properties can be obtained by their melt compounding. Additionally, PPC and POM can be processed at the same temperature and due to their chemical structures which contain polar groups, there is the potential for strong intermolecular interactions such as dipole-dipole in the blend. ...
Poly(propylene carbonate) (PPC) is a promising new sustainable polymer produced from carbon dioxide. PPC has inferior thermal stability which could be enhanced by synergistic blending with other polymers. Blends of PPC and the engineering thermoplastic polyoxymethylene are produced by melt compounding in various weight ratios. The compatibility of the blends is investigated using thermogravimetric analysis (TGA), differential scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), density measurements, and scanning electron microscopy (SEM). TGA reveals that thermal stability of the blends increases dramatically in comparison to the neat PPC. A small shift in the glass transition temperature demonstrates the immiscibility of the blends but also indicates some compatibility, attributed to potential dipole–dipole interactions which are also corroborated with the FTIR results. A deviation of the rule of mixtures for density is found for some of the blends. SEM analysis of the blends shows two phase morphology; however, the interfacial adhesion appeared to be enhanced with increasing PPC content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 135, 45823.
... For example, thermoplastic polyurethane (TPU) as an excellent elastomer was reported to possess compatibility with POM due to the effect of hydrogen bonds [6]. The TPU modified POM has been researched extensively [7][8][9][10][11][12]. However, TPU is expensive, other elastomers are sought to modify POM. ...
Ternary blends of polyoxymethylene (POM), polyolefin elastomer (POE), and glycidyl methacrylate grafted high density polyethylene (GMA-g-HDPE) with various component ratios were studied for their mechanical and thermal properties. The size of POE dispersed phase increased with increasing the elastomer content due to the observed agglomeration. The notched impact strength demonstrated a parabolic tendency with increasing the elastomer content and reached the peak value of 10.81 kJ/m2 when the elastomer addition was 7.5 wt%. The disappearance of epoxy functional groups in the POM/POE/GMA-g-HDPE blends indicated that GMA-g-HDPE reacted with the terminal hydroxyl groups of POM and formed a new graft copolymer. Higher thermal stability was observed in the modified POM. Both storage modulus and loss modulus decreased from dynamic mechanical analysis tests while the loss factor increased with increasing the elastomer content. GMA-g-HDPE showed good compatibility between the POM matrix and the POE dispersed phase due to the reactive compatibilization of the epoxy groups of GMA and the terminal hydroxyl groups of POM. A POM/POE blend without compatibilizer was researched for comparison, it was found that the properties of P-7.5(POM/POE 92.5 wt%/7.5 wt%) were worse than those of the blend with the GMA-g-HDPE compatibilizer. POLYM. ENG. SCI., 2017.
... TPU is a kind of thermoplastic resin, so the fabrication of the composite material is made by a hotpressing process. Reading reference literature of hot-pressing molding process parameters [5][6][7], the authors determined the optimum hot-pressing parameters as being: pressure 0.5 MPa, hot-pressing time 120s and hot-pressing temperature 110 ℃. The non-woven was decorated in processing mould plate vulcanizing machine, when the temperature rose to 110 ℃. ...
In order to study the influence of resin content and layer sequence parameters on the mechanical properties of TPU/non-woven composite materials synthesized by moulding pressing technology. The effects of the resin content and layer sequence on composites were discussed. Through experiments and theoretical analysis, it was revealed how resin content, layer sequence impact on mechanical properties of composite. The mechanics properties of TPU/non-woven composite materials are improved. The process is pressure 0.5 MPa, temperature 110 °C and time 120s min. The melting of the TPU infiltrated into the fabric and filled the space between the fibers.
... The available literature primarily deals with the improved mechanical, wear and thermal behaviors of CNT/POM. So far, only a handful of research works has been published on the effect of rheological parameter variation by using rheometrics system (parallel or cone plates) and capillary viscometer.111213141516 The evaluation of melt rheological properties of POM and its composites in terms of complex viscosity, storage modulus and loss modulus with angular frequency is important. ...
The paraffin oil dispersion technique innovated in the recent years to synthesize bulk polymer nanocomposite materials has a uniform dispersion. This research work aims to study the effect of added carbon nanotubes (CNTs) on flexural, impact and rheology behaviors of polyoxymethylene (POM) reinforced by 0–0.03 wt% of CNT using paraffin oil dispersion technique. The wettability and lamellar thickness were measured and rheological performance investigated using a parallel plate rheometer. The flexural and impact mechanical properties were also evaluated. The fracture surfaces were then examined by microscopy. The results showed that the energy to break, flexural strength and modulus increased proportionally with the addition of the amount of CNT in the matrix. For the rheology behavior, the viscosity decreased at the low percentage of CNT and then increased with increase in the percentage weight ratio of CNT in the POM matrix. It was also noted that the water contact angle rose with the increase the CNT percentages. Copyright
... Thermoplastic polyurethane (TPU), which possesses excellent combined performances in toughness, durability, flexibility, biocompatibility, and biostability, is applied to toughen polypropylene (PP), poly vinylidene fluoride (PVDF), polyamide (PA), polyacetal and so on. [12][13][14] However, the application of TPU in toughening PPS is seldom reported possibly considering the relative poor high temperature stability. In this paper, the strong toughening effect was found in Sr-ferrite/PPS/TPU composite system and the influence mechanism of TPU on PPS-based composites was also explored. ...
In order to improve the impact strength of PPS-based strontium ferrite composite, the thermoplastic polyurethane (TPU) elastomer was added in the composite as a toughening agent. The composites were obtained by melt-blending PPS, TPU and strontium ferrites in twin-screw extruder. The crystalline state, thermal property, surface morphology and impact strength of the composites were investigated by using X-ray diffraction, differential scanning calorimetry, thermoravimetric analysis, scanning electron microscope and izod impact test. The addition of TPU improves impact strength of PPS-based strontium ferrite composite. When the addition of TPU increases to 11wt %, the impact strength of Sr-ferrite/PPS/TPU composite is enhanced by 51.44% compared with the sample without TPU addition, and reaches to 5.77 kJ/m2. The occurrence of bonding interaction between PPS and TPU, demonstrated by a series of experiments, changes the structure and impact properties of PPS. Based on the experimental results, a possible mechanism is proposed to explain the improvement of Sr-ferrite/PPS/TPU composites, which is different from the conventional toughening mechanism by the conformation of elastomers and the suppression of microcracks propagation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43564.
... Borggreve et al. 6 concluded that the impact strength of polyamide6 (PA6) is only moderately improved by blending with Arnitel EL315. Palanivelu et al. 7 have investigated the tensile and flexural strength of the blends decreased with increasing TPU concentration. However, the impact strength increased with increasing TPU concentration in POM blends. ...
Short fibers and particulate fillers are known to enhance the mechanical properties of the polymers. The type of fiber and filler morphology, size, loading, and dispersion homogeneity influence extensively the composite’s performance. In the present study, various amounts of short fiber (glass and carbon) and micro-scale particles (silicon carbide, alumina and molybdenum disulphide) were systematically introduced into thermoplastic copolyester elastomer/polytetrafluroethylene (TCE/PTFE) composite for reinforcement purpose. The influence of these fibers and fillers on the tensile, flexural, and impact properties was investigated. All composite samples were fabricated using twin-screw extruder followed by injection molding. The incorporation of short glass fiber (SGF) yielded an effective improvement in mechanical properties of TCE/PTFE composite at a fiber loading of 20 wt.%. Choosing the 20 wt.% SGF-reinforced TCE/PTFE composite, short carbon fiber and microparticles were further added in order to achieve additional improvement in the mechanical properties. In fact, synergistic effects were in the form of a further increase in hardness, tensile modulus, flexural and impact strength. Various reasons to explain these effects in terms of reinforcing mechanisms were discussed. Also, dispersion of the fiber and fillers were studied using scanning electron microscopy.
... Hashemi et al. [2] studied the relationships among mechanical properties in glass-filled polyoxymethylene. Palanivelu [3] investigated the effects of a twin screw extruder modeled on the mechanical, morphological and rheological properties of polyacetal thermoplastic polyurethane blends, using various amounts of thermoplastic polyurethane in polyacetal thermoplastic polyurethane blends. Kastelic et al. [4] examined the effects of an extrusion molding on the mechanical properties of fiber-reinforced polyoxymethylene; they explained the observed mechanical properties in terms of grain size and grain boundary voids. ...
This study investigates the influence of process conditions on the tensile properties of polyoxymethylene (POM) composites that contain three amounts of glass fiber-reinforcement (0 wt%, 15 wt% and 25 wt%). Four processing parameters - orientation of fiber, thickness of fiber layer, amount of fiber, and injection molding parameter were considered. The morphology of the fiber layer is observed by scanning electron microscopy (SEM), to elucidate the correlation between the orientation of the fibers and the mechanism of fracture of the bucking surface. The experimental results show that the maximum ultimate stress is obtained at a filling time of 1.5 s, a melt temperature of 215°C, a mold temperature of 75°C, and a packing pressure 75 MPa. SEM revealed that the composite contained two distinct layers. The fibers in the frozen layer were parallel to the melt flow, while the fiber was perpendicular to the melt flow in the core layer. The thickness of the frozen layer increased with the amount of fiber, increasing tensile strength. Additionally, fiber pullout and across-matrix cracking are the main fracture mechanisms of the frozen layer, whereas failure of the fiber-matrix interface is the major fracture mechanism in the core layer.
... This may be attributed to the incompatibility of POM with most of rubbery impact modifiers as a fact that the special molecular structure of POM leads to a poor interfacial adhesion between POM matrix and rubber phases [5]. One of the few describes a dramatic improvement in impact toughness by the incorporation of thermoplastic polyurethane [26]. However, addition of rubbery impact modifiers also reduced the stiffness and rigidity of POM, and thus resulted in a negative effect on the tribological performance. ...
A novel type of polyoxymethylene (POM)-based composites with polytetrafluoroethylene (PTFE) fiber and poly(ethylene oxide) (PEO) was prepared via melt extrusion in order to enhance the friction lubrication and wear resistance of POM. The tribological experiments demonstrated that the coefficient of friction and wear rate of POM were both reduced by the incorporation of PTFE fiber, and furthermore, the higher the loading of PTFE fiber the better the tribological properties. The wear mechanism is derived from the thin film of PTFE formed on the contact-surfaces during sliding. The addition of PEO into POM/PTFE fiber composites can enhance the formation of transfer film on the mating surfaces during sliding contact, and thus further improves the friction and wear performance. The wear behaviors also depend on the normal loading and sliding duration, under which the transfer film could form appropriately. In addition, the abrasion of the dispersed PEO domains in matrix is also helpful to the heat dissipation when the counter-surface exerts oscillating forces on the POM surface. It should be emphatically mentioned that the use of PTFE fiber as tribological additive can improve the notched impact strength of POM, and the subsequent incorporation of PEO leads to a more significant toughening effect for POM. The morphological investigation reveals that the toughening effect is attributed to the dissipation of impact energy through the pullout of PTFE fiber and the plastic deformation of the POM matrix induced by PEO. Polarized optical microscopy demonstrates that the presence of PEO can interfere in the crystallization of POM and reduced the size of spherulites, and consequently weakened the sensitivity to notch. Although the POM-based composites underwent a different mode of thermal degradation from neat POM with a slight reduction in the temperature at rapid weight loss, their thermal stabilities were maintained well enough to meet the requirement for its application.
... The literature survey reveals that most of the investigations were carried-out through interpenetrating polymer network/solution process using a thermosetting type of polyurethane (PU) and different acrylic materials (2 -7). However, thermoplastic polyurethane (TPU) may be mixed with poly(ethylene-co-methyl methacrylate) (8), polyolefins (9), polypropylene (PP) (10), styrene-acrylonitrile (SAN (11), polyacetal (12), poly (butyleneterephalate) (13), polycarbonate (PC) (14), acrylonitrile-butadiene-styrene (ABS) (15), polyamide-6 (16), etc., from the point of improving the mechanical properties particularly such as toughness and other properties. PMMA is a transparent polymer with good tensile properties and oil resistance, while TPU is a thermoplastic elastomer used extensively in the automotive and coating industries because of its easy processability with good elongation, excellent low temperature properties and high abrasion resistance. ...
Blends of poly(methyl methacrylate) (PMMA) and thermoplastic polyurethane (TPU) in different compositions viz., 95/5, 90/10, 85/15 and 80/20 (by wt/wt, % of PMMA/TPU) were blended by melt mixing using a twin‐screw extruder. All the PMMA/TPU blends have been characterized for physico‐mechanical properties such as density, melt flow index, tensile behavior and izod impact strength. The impact strength of the PMMA/TPU blends were found to increase significantly with an increase in the percentage of TPU up to 20%, by retaining the tensile strength of PMMA. The effect of chemical aging on the performance of blends has been studied.
In this study, the thermal, rheological, mechanical, and viscoelastic properties of two new-generation thermoplastic polymers, namely cyclic olefin copolymer (COC) and polycarbonate urethane (PCU) elastomers, were compared to those of a conventional thermoplastic elastomer, thermoplastic polyurethane (TPU). Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used for thermal examinations, while rheological, tensile, and solid-state creep tests were used for viscoelastic and mechanical analyses. The DSC results revealed that all elastomers had two different T g values, which were −23 and 7.5°C for PCU, −40 and 95°C for TPU, and 4 and 55°C for COC. Moreover, PCU had an amorphous and more compatible structure than PCU and TPU. In the DMA, it was also observed that COC melted at approximately 90°C, while PCU and TPU melted at about 155°C. In the tensile tests, it was observed that COC showed higher strength at 30°C, but it lost its strength more effectively than the other polymers with increasing temperature and exhibited similar performance to all specimens at 50°C. Finally, in the solid-state creep tests, COC exhibited the highest creep resistance at 30°C, while its creep strain increased with temperature more effectively than those of the other elastomers.
Unique hybrid thermoplastic composites based on polyoxymethylene copolymer (POM C), 10 wt.% glass fiber (GF) and graphite (Grt) filler at 1, 3, and 5 wt.% were developed using injection molding technique. According to the Taguchi L16 orthogonal array, present experiments were carried out with the aim of determining the coefficient of friction (COF) and specific wear rate ( SWR ) under a range of loads (namely, 5, 10, 20, and 30 N), sliding speeds (namely, 200, 400, 600, and 800 rpm), and run times (namely, 15, 30, 45, and 60 min) with varying wt.% of Grt (namely, 1, 3, and 5 wt.%) throughout the experiment. Analysis of variance (ANOVA) was used to evaluate the most significant factors that affect the output functions (viz., COF and SWR ). The findings demonstrated that POM C/10GF composites' tribo‐mechanical, structural, and thermal properties were considerably improved upon by including Grt. Various microscopical methods were also employed to study the wear mechanisms of the composites and the surface morphology of the worn samples. The POM C/10GF with a 3 wt.% of Grt exhibited superior tribological properties owing to its enhanced interfacial bonding characteristics, resulting to increased wear resistance.
Highlights
Injection molded POM C/10GF hybrid composites with 1, 3, and 5 wt.% graphite (Grt)
Structural, thermal, chemical, tribo‐mechanical and microstructural studies
Design of experiment with variable loads, times, speeds, and Grt compositions
COF and specific wear resistance as response
Optimization of hybrid composite composition using Taguchi L16 orthogonal array
POM, TPU, carbon black nanoparticle, impact resistance, morphology H ypothesis: The effect of carbon black nanoparticles and thermoplastic polyurethane on the tensile strength and impact properties of polyacetal (POM), which is widely used in the application of automotive parts such as bumper brackets, has been investigated. Improving the impact resistance of polyacetal is one of the challenges of automotive industry, which would diminish the car damage in accidents. The incorporation of thermoplastic polyurethane into the polyacetal matrix can create good compatibility and increase its impact resistance. In addition, the presence of carbon block in the polyacetal matrix can simultaneously elevate the tensile strength and impact resistance and increase the UV resistance of polyacetal. Methods: Standard mechanical testing specimens of the POM/CB/TPU nanocomposites, containing 0.42% (by wt) carbon black and different fractions of 2.5, 5 and 7.5 % (by wt) of thermoplastic polyurethane (TPU) were produced through a twin-screw extruder and injection molding. Standard tensile and impact tests were performed to evaluate the mechanical performance of nanocomposites. The morphology of fractured surfaces of impact specimens and the toughening mechanisms were investigated using scanning electron microscopy (SEM). Findings: The results of tensile test showed that the presence of carbon black nanoparticles increases the Young's modulus and the tensile strength of polyacetal. However, the inclusion of thermoplastic polyurethane into the POM/CB reduced the tensile behavior. The incorporation of a phase with soft segments to the polymeric matrix with hard segments reduces the tensile strength. In addition, the carbon black and the thermoplastic polyurethane increase the elongation-at-break of this three-phase nanocomposite. The results of impact test showed that the presence of carbon black nanoparticles and thermoplastic polyurethane in the polyacetal matrix leads to enhanced impact resistance. Plastic deformation, crazing, fibrillated structure and microvoid were the dominant toughening mechanisms in nanocomposites.
Currently, a variety of chemical compounds are being used as Flame-retardants (FRs) and they can be classified according to the type of element present.
Different loadings of organo-montmorillonite (OMMT) were mixed with ultra-high molecular weight polyethylene (UHMWPE)/polypropylene (70/30) composites under elongation flow. Results showed that ideal dispersion of OMMT nanoparticles could be achieved and most OMMTs intercalated and exfoliated effectively. However, the layer spacing of OMMT decreased with the increase in the content of OMMT. UHMWPE was surrounded by the OMMT layers, and its shape evolved from a compatible phase to a sphere. OMMT caused heterogeneous nucleation in the blends, leading to a high crystallisation temperature. Meanwhile, the intercalated and exfoliated OMMTs promoted the motion of polymer chains, and inhibited the crystallisation process of UHMWPE in the composites. The crystallinity of UHMWPE with 5% OMMT markedly decreased from 48.39% to 41.46%. Various rheological analyses confirmed that the complex viscosity of composites and the storage modulus decreased first and then increased with the increase in the content of OMMT. UHMWPE/PP with 5% OMMT exhibited the ideal mobility.
Polyurethane (PU) is a versatile polymer because of the various structures of isocyanate, polyols, and chain extenders. The structure of the hard segments and soft segments can be tailored to fit different applications. Polymer blends and interpenetration networks (IPNs) are cost effective ways to produce engineering materials with superior properties. Different types of PU can be readily used in blending with various polymeric materials or fabricated PU IPNs for a variety of applications. In this chapter, the role of the nanofillers in the blends/IPNs will be discussed extensively. The structure of the PU used in the blends/IPNs, the preparation methods, and the properties improved are reviewed for the guidance of future research directions. The future perspectives of PU based blend/IPNs in term of preparation are suggested.
Biobased blends of commercially available polyester based bio thermoplastic polyurethane
(TPU) and castor oil based polyamide 11(PA11) of different ratios are prepared by melt
processing. The blends properties such as shape memory behavior through unconstrained and
constrained recovery, interfacial interaction, morphology, dynamic mechanical, rheological,
and mechanical behavior are studied. A strong interface between the two polymeric phases
due to hydrogen bonding observed through morphology indicates that TPU and PA11 are well
compatible. The complex viscosity of blends ranges between that of neat PA11 and TPU.
Thermal analysis shows that higher the TPU content lower the melting point (Tm)
corresponding to PA11 and the crystallization temperature (Tc) remains unaltered. Adding
TPU to PA11 ductility and impact strength of the blends increases significantly with the small
reduction in their tensile strength. Shape memory behavior investigation reveals that, blends
recover almost 95% of the applied deformation when heated at zero load and they recovered a
stress of 1.8 MPa to 3.2.MPa in constrained recovery during three consecutive
thermomechanical cycles. The reported results on bio-alloys promotes the usage in
multidisciplinary field of intelligent devices such as ergonomic grips and sports shields.
Long glass fibers reinforced thermoplastic polyurethane and poly (butylene terephthalate) with the compatibilizer of poly (ethylene-butylacrylate-glycidyl methacrylate copolymer) (LGF/TPU/PBT/PTW) composites were prepared by using self-designed impregnation device. Various rheological plots including viscosity curve, storage modulus, loss modulus, loss angle, Cole-Cole plot, and relaxation spectrum were used to characterization of rheological properties. Dynamic mechanical thermal analysis (DMA) results indicated that “double tanδbehavior” of composites is observed. The activation energies of α and β-relaxation process of loss modulus and tan δ of the LGF/TPU/PBT/PTW composites gradually increased with long glass fibers content. Moreover, activation energies for the glass transition relaxation determined from loss tangent peaks are more reliable than using loss modulus criterion. Thermal properties of composites are studied by differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA). Mechanical properties of composites are studied. POLYM. COMPOS., 2016.
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 polyformaldehyde (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 tests results indicated the 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 small amount of IC-TPU. The investigation indicated that the IC-TPU exhibited the novel structure with the soft shell (uncovered TPU) and hard core (β-CD covered TPU segments). Such “soft shell-hard core” structure improves not only the elongation at break but also the tensile strength of POM. The superior thermal stability was originated from the synergetic effects of the hydroxyl groups in β-CDs and the amino groups in TPU. The multifunctional effect of the IC-TPU opens the new avenue for the industrial application of POM.
The blends of polyoxymethylene (POM)/thermoplastic polyurethane elastomer (TPU), POM/TPU/isocyanate oligomer (Z) and POM/TPU/Z/polyether were prepared by using twin-screw extruder. Mechanical properties, crystallization behavior and morphology were studied through mechanical properties testing, differential scanning calorimetry (DSC), polarizing microscopy (PLM), Fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM) and dynamic mechanic analysis (DMA). The results showed that with increasing content of TPU, elongation at break and notched impact strength of the blends increased. Z and polyether played an important role in promoting the dispersion of TPU in POM and enhancing compatibility of two phases. The crystallinity of POM in the blends decreased. Elongation at break and notched impact strength of the blends were improved.
In the study, a polyurethane prepolymer (PU) was first synthesized, then mixed with CMC in various ratios, the resulting mixture appearing as a thin membrane; finally, the compatibility of the mixture was tested by FTIR, DSC, SEM and X-ray analyses. The results show that the PU/CMC blended polymer with higher PU ratios evidences hydrogen bonds, meaning that the two components are partially compatible.
In this study, with the glass fiber reinforced Polyoxymethylene composite material as the subject, we examined the impact of different injection molding process parameters such as melt temperature, mold temperature, packing pressure, injection speed and packing time on mechanical properties. We designed the experiment by using the orthogonal array of Taguchi method, and obtained the single quality characteristic optimization parameters by using the main effect analysis and variance analysis of Taguchi method. Based on the experimental quality data, we integrated principal component analysis and grey relation analysis to identify the combination of multiple quality characteristics optimal process parameters. As the research results suggest, if the four quality characteristics including tensile strength, hardness, impact strength and bending strength are considered, the optimal conditions are glass fiber content of 20 wt%, melt temperature 230 °C, mold temperature 60 °C, packing pressure 50 MPa, injection speed 60 mm/s and packing time 1.5 s. Finally, it was verified that the planned experiment of this study can effectively enhance the material’s multiple quality characteristics with good reproducibility.
Introduction Density Hardness Heat Capacity Melt Flow Water Absorption Gas Permeability Specific Absorption
In this work, acrylonitrile-styrene-acrylic terpolymer/styrene-acrylonitrile copolymer/hydrogenated nitrile rubber (ASA/SAN/HNBR) ternary blends with different composition were prepared by melt blending. Properties of the ternary blends were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMTA), Fourier transform infrared spectra (FTIR), heat distortion temperature (HDT), melt flow rate (MFR), and Scanning electron microscopy (SEM). The results showed that the incorporation of HNBR can enhance the toughness by a large scale, and the two rubber phase showed partial miscibility. Heat resistance of the blends almost unchanged with HNBR content. FTIR told that the preparation of the ternary blends was a physical process, and no obvious phase separation was observed in SEM images.
Amorphous copolyester/polyoxymethylene (POM) blends were produced by melt blending covering the whole composition range. As copolyester poly(ethylene glycol-co-cyclohexane-1, 4-dimethanol terephathalate) (PETG) was selected. Injection and compression molded specimens of the blends were subjected to various rheological, thermal, thermomechanical and mechanical investigations. Many properties of these incompatible PETG/POM blends followed the additivity rule as a function of composition, such as melt flow index, density, tensile and flexural stiffnesses. However, the elongation at break, energy absorbed until tensile failure, flexural strength, notched Izod impact strength and static fracture toughness, K c showed lower values than either of the neat blend components. This was traced to the poor interfacial adhesion between PETG and POM. A co-continuous morphology was ascertained by the combination of selective extraction and scanning electron microscopy (SEM) for the blends PETG/POM=60/40 and =50/50 wt%/wt%. The tensile fracture surface of the 50/50 blend exhibited a fibrillar morphology owing to the injection molding-induced distortion of the initial co- continuous phase structure.
In this work, (acrylonitrile-styrene-acrylic terpolymer)/(styrene-acrylonitrile copolymer)/(powder nitrile butadiene rubber) ternary blends with different compositions were prepared by melt blending. Differential scanning calorimetry, dynamic mechanical analysis, and Fourier-transform infrared spectra were used to analyze the glass transition behavior and interactions among components of the blends, while scanning electron microscopy was used to observe the microstructure. Furthermore, mechanical properties, heat resistance, and melt flow rate of the blends were tested. The results showed that addition of powder nitrile butadiene rubber can enhance toughness of the blends on a large scale, and the blend system seems to be miscible according scanning electron microscopy images. J. VINYL ADDIT. TECHNOL., 2014. © 2014 Society of Plastics Engineers
Thermoplastic polyurethane (TPU)/poly (butylene terephthalate) (PBT) blends with different ratios were prepared by extrusion and injection molding. The morphology, dynamic viscoelastic, capillary rheological, thermal and mechanical properties of the blends were studied. Results showed that there was good compatibility between TPU and PBT. The capillary rheological properties showed that the apparent viscosity decreased with the TPU content. DSC analysis indicated that with increasing TPU content the crystallization temperature (Tc), the melting point (Tm) and the percent crystallinity (Xc) decreased. Mechanical properties showed that the addition of TPU could lead to a remarkable increase, about 368.18%, in impact strength with a small reduction in tensile and flexural strength of TPU/PBT blends.
Here, we report the morphology and properties of melt-blended poly(acrylonitrile-butadiene-styrene) (ABS) toughened polyoxymethylene (POM)/clay nanocomposites at different clay loadings (2.5 and 5 phr). The number average domain diameter (Dn) of the ABS droplets in the (75/25 w/w) POM/ABS blend was gradually decreased with increase in clay loading. The X-ray diffraction (XRD) study and transmission electron microscopic (TEM) analysis of the (75/25 w/w) POM/ABS/clay nanocomposites revealed that, the major amount of clay silicates was dispersed selectively in the POM phase of the blend with an exfoliated morphology. The thermal stability of the (75/25 w/w) POM/ABS blend was increased with the increase in clay loadings. Differential scanning calorimetry (DSC) study suggested the enhancement in the non-isothermal crystallization temperature of the matrix polymer in the blend/clay nanocomposites. The rheological study revealed a shear thinning behavior in the nanocomposites indicating good processability of the nanocomposites. The solvent uptake property of the blend was decreased in the presence of small amount of the clay in the nanocomposites. The tensile strength and Young modulus of the (75/25 w/w) POM/ABS blend were increased, whereas, percent elongation of the blend was decreased with increasing the clay content. The toughening effect of the ABS was prominent in the POM/ABS/clay nanocomposites compared to the pristine polymer. POLYM. COMPOS., 35:273–282, 2014. © 2013 Society of Plastics Engineers
The blends of thermoplastic polyurethane (TPU) with natural rubber (NR) were prepared via melt mixing technique, at four different blending temperature at range 180°C - 210°C and mixing times of 8, 10, 12, 14 min. The effects of both mixing parameters on tensile strength of the blends were investigated. The blend of 85TPU15NR shows the maximum tensile strength at 180°C and 10 min mixing. The viscosity of the polymer blends will decrease as the temperature increased. The movements of molecules are more worthy because of the poor molecules interaction. The increasing of mixing time will increase the compatibility of the blends and also increase in mechanical properties. Mixing time and mixing temperature are important parameters in acquiring blends having optimum mechanical properties.
This study investigates the influence of two process conditions on fiber orientations and tribological characteristics of POM/GF composites. The morphologies of fiber layers were observed to elucidate wear mechanisms, and the correlation between fiber orientation and fiber layer thickness. Experimental results indicate that there are three distinct layers from top surface to the core—a solidified layer, intermediate layer, and core layer. The tribological characteristics decreased as thickness of solidified layer decreased. Furthermore, minor grooving and debonded fibers were the major wear mechanisms for P-direction specimens. Severe cracks and cut fibers were the major wear mechanisms for AP-direction specimens.
Acrylate elastomer (ACE) synthesized ourselves was mixed with antioxidative and UV stabilizer into polyoxymethylene (POM) matrices to investigate the effects of the ACE phase on the mechanical properties and UV stability of POM. For comparison, POM blended with same amount of TPU instead of ACE was used. Dispersion of the elastomer particles in POM matrices was investigated using SEM micrograph. Crystallinities of the specimen before and after UV ageing were also measured. The surface molecular weight and the mechanical properties of modified POM after UV ageing were determined. The result showed that excellent mechanical properties of the POM composites after UV‐irradiation could be obtained by blending with ACE.
The polymer blends of polyoxymethylene (POM) and gel acrylonitrile- butadiene elastomer (GNBE) with phenol formaldehyde resin (PFR) as the compatibiliser were prepared, and the structure and properties were studied. The results show that GNBE is an excellent toughening agent for POM. The blend POM/GNBE (80/20) with 6 phr PFR attains a notched Charpy impact strength of 21 -6 kJ mT-2, an elongation at break of 133% and a tensile strength of 33-8 MPa. PFR is incorporated into GNBE and the hydroxyl groups in PFR form intermolecular hydrogen bonds with POM. Dynamic mechanical analysis studies show that POM and GNBE are partially miscible and the miscibility of the blends is improved by PFR. The results from TEM show that the size of the dispersed phase of the ternary blends decreased with increasing PFR content in the blends. A rubber band of GNBE dispersed phase and a complex wrapped structure in POM were observed in the POM/GNBE and POM/GNBE/PFR blends.
Most studies on polymer tribology are traditionally performed on small-scale test specimens. However, to obtain data relevant for practical design of polymer parts used in high load/low sliding velocity systems one must simulate real working conditions as close as possible on laboratory scale. A large-scale test rig has presently been used for determination of friction and wear behaviour of a commercial polyoxymethylene homopolymer (POM-H). Test results are compared to those obtained on a small-scale cylinder-on-plate configuration, investigating possibilities for extrapolation. For small-scale tests, a transition is found from pure adhesive/abrasive wear to deformation and softening when the calculated bulktemperature exceeds 90°C, corresponding to stabilisation in friction. Overload conditions occur at higher temperatures due to the lack of polymer transfer. Softening and melting of large-scale polymer samples allow for huge transfer films, providing low to extremely low friction and stabilisation in wear rates. Although a thermal extrapolation model with a macroscopic geometry factor is evaluated, friction and wear rates cannot be estimated from small-scale tests because of differences in wear mechanisms, influenced by transfer ability, creep and contact area.
Rubber toughening of an amorphous polyamide (Zytel 330) using combinations of triblock copolymers of the type SEBS and a maleic anhydride functionalized version, SEBS-g-MA, was investigated and the results compared with those of nylon 6 and nylon 66. The effects of rubber content and the type of extruder on the morphology, Izod impact behavior and the ductile–brittle transition temperature were explored. The shape and sizes of the rubber particles in blends with this amorphous polyamide were found to be more similar to those in nylon 6 than in nylon 66 blends. The twin screw extruder produced smaller particles with a more narrow distribution of sizes than the single screw extruder. Higher rubber contents generally yielded tougher blends; there is a critical rubber particle size above which the ternary blends are brittle at 20wt% total rubber. The ductile-to-brittle temperature was found to decrease with increased rubber content and decreased rubber particle size. In general, the trends for this amorphous polyamide are rather similar to those reported earlier for semi-crystalline nylon 6 and nylon 66.
The cationic polymerization of 1,3,5-trioxane, 1,3-dioxolane and a small amount of 2-hydroxyacetic acid (HAA) was carried out, and the resulting modified-polyacetal (POM) was blended with thermoplastic polyurethane (TPU) in melt. The results of 1H NMR analysis indicated that HAA was almost incorporated in the modified-POM, and that the resulting carboxyl end-group and hydroxyl end-group in the modified-POM reacted with TPU during the melt blending. There were many boundary layers between the cavities and matrix in the modified-POM/TPU (82/18 by weight) blend that was etched with tetrahydrofuran (THF), and the diameter of the cavities became ∼0.3–1 μm long when the blending time reached 10 min. The results of scanning electron microscopic (SEM) observation and dynamic mechanical analysis (DMA) indicated that the modified-POM/TPU blend had a good compatibility because of the interfacial reaction between the modified-POM and TPU phase in the blend. The modified-POM/TPU blend exhibited higher Charpy impact strength when compared with a normal-POM/TPU blend; the toughness of the modified-POM/TPU blend attributed to the good compatibility between the two phases. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4375–4382, 2006
The main goal of this study was impact modification of polyacetal [polyoxymethylene (POM)] with thermoplastic elastomer polyurethane (TPU). We modified the impact strength of POM 10-fold. The mechanical properties, thermal behavior, and morphology of POM/TPU blends consisting of 5 to 50% of TPU were studied. It was found that the best impact modification of the blends was at 15% concentration of TPU and the maximum elongation at break was at 30% concentration of TPU. The impact strength of POM/TPU blends can be improved by using diphenylmethane diisocyanate (MDI) as compatibilizer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2573–2582, 2002
Due to its “unzipping” degradation mode and poor compatibility with most other flame retardants, polyoxymethylene (POM) is the most difficult flame-retarded polymer among macromolecular materials. In this project, we took advantage of thermoplastic polyurethane (TPU) resin, which possesses good compatibility with POM, serving as an encapsulation layer, and the carrier resin of the nitrogen-phosphorus composite flame retardant melamine phosphate to achieve even and fine dispersion of the flame retardant particles in the POM matrix. The improved morphology of the dispersion phase can markedly modify the flame retardancy and good mechanical performance. Additionally, the encapsulation of TPU avoids direct contact of the flame retardant with POM, thus also advantageous to the enhancement of its material performance. Moreover, as an efficient formaldehyde absorbent and toughening agent, TPU itself can greatly improve the flame retardancy, thermal stability, and toughness of the flame retardant POM. Therefore, this method provides a simple and effective method to prepare flame retardant POM with good comprehensive performance.
To determine the possibility of using polytetrafluoroethylene (PTFE) powder as reinforcing filler in the thermoplastic matrix, the thermoplastic polyurethane (TPU) as the matrix and PTFE powder as reinforcing filler were used to prepare a particulate reinforced composite, in order to determine testing data for electrical and mechanical properties of the composites according to the filler loading in respect to TPU polymer matrix. The TPU and PTFE powder composites were prepared by the milling TPU with 2.5, 5, 7.5, and 10 wt% of PTFE powder in a two roll mill and the milled material is compression moulded to make sheets. From the sheets, the test specimens were made and tested for electrical properties—dielectric strength, dielectric constant, surface, and volume resistivity; fire resistance—rate of burning; mechanical properties—tensile strength and elongation, impact strength, hardness; density and melt flow index. The incorporation of PTFE powder has significantly improved the electrical properties—dielectric strength, dielectric constant, surface and volume resistivity; and fire resistance—rate of burning of thermoplastic polyurethane. However, the tensile strength decreased from 24.91 to 14.71 MPa and tensile elongation increased from 620 to 772 percentage.
This study investigates the influences of two processing conditions on wear properties of Polyoxymethylene (POM) polymer, and further determines the optimal parameter setting for the injection molding process to achieve optimal wear quality. This study uses two experimental designs, including the conventional single factor design and Taguchi L9 orthogonal design. Moreover, morphology of worn surfaces was analyzed by scanning electron microscopy (SEM). Analytic results confirm that combining the Taguchi experimental design with the analysis of variance (ANOVA) can link controlled parameters and targeted output, and rapidly predict the optimal parameter settings for various injection-molding conditions.
This study made use of poly(ethylene glycol) (PEG) samples of different molecular weights, which were reacted with a diisocyanate ester, and an anion center for the synthesis of polyurethane (PU), which was then mixed with chitosan to form a polymer adsorbent. It was tested for the determination of its adsorption toward acidic dyestuffs under various conditions. Our results showed that under all the tested conditions, the blended polymer adsorbent possessed a better adsorbing ability than chitosan by itself, and the degree of adsorption varied positively as the adsorbent concentration, ambient temperature, and contact time increased. Furthermore, the addition of PU remarkably increased the adsorption efficiency, whereas PEG with a greater molecular weight yielded a better adsorption performance. As for the dyestuffs, the red one surpassed the others in adsorption efficiency. Finally, a 5 mg/mL concentration of the adsorbent solution, a temperature of 45°C, and a contact time of 15 min gave fairly good adsorption results. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3991–3998, 2004
Polyoxymethylene (POM)/elastomer/filler ternary composites were prepared, in which thermoplastic polyurethane(TPU) and an inorganic filler, CaCO 3 , were used to achieve balanced mechanical properties of POM. A two‐step processing method, in which the elastomer and the filler were mixed to a masterbatch first and then the masterbatch was melt‐blended with pure POM, was used to obtain a core‐shell microstructure with CaCO 3 covered by TPU. A brittle‐ductile transition phenomenon was observed with increasing TPU content for this ternary system. To better understand the toughening mechanism, we investigated the fractured surface, interparticle distance, and the spherulite size of POM as function of the TPU and CaCO 3 content. The critical TPU content depended on not only the content of CaCO 3 , but also the size of CaCO 3 particles. The observed brittle‐ductile transition was discussed based on the crystallinity and spherulite size of POM as well as Wu's critical interparticle distance theory. The results showed that the impact strength of POM/TPU/CaCO 3 ternary system depends on a critical, interparticle distance, which varies from one system to another. The dependence of the impact strength on the spherulite size was considered for the first time, and a single curve was constructed. A critical spherulite size of 40 micron was found, at which brittle‐ductile transition occurs, regardless of the TPU and CaCO 3 content or the size of CaCO 3 particles. Our results indicate that the spherulite size of POM indeed plays a role in determining the toughness, and must be considered when discussing the toughening mechanism.
Izod impact strength vs. the crystal size for POM/TPU blends and POM/TPU/CaCO 3 ternary composites.
magnified image Izod impact strength vs. the crystal size for POM/TPU blends and POM/TPU/CaCO 3 ternary composites.
Co-continuous amorphous copolyester (PETG)/polyoxymethylene (POM) (50/50 wt%/wt%) blends were prepared using a twin screw extruder followed compression molding. Two types of thermoplastic polyurethane (TPU) (i.e., polyester-based and polyether-based) were used to compatibilize the blends system. The thermal properties were characterized by using differential scanning calorimetry (DSC). The mechanical properties of the co-continuous PETG/POM blends were studies through flexural and single-edge notch tensile test (SEN-T). The SEN-T test was performed at three different testing speeds; 1, 100, and 500 mm/min. Scanning electron microscope (SEM) was used to access the fracture surface morphology. The flexural strength of the PETG/POM blends was decreased in the presence of TPU. This was attributed to the elastomeric nature of the TPU. The compatibilizing effects of TPU on the PETG/POM blends were proven by moderate improvement in the fracture toughness and confirmed by the SEM observation. The SEN-T fractured surface of the compatibilized blends showed gross matrix shear yielding as compared to the uncompatibilized system. The Kc values of the PETG/POM blends decreased as the testing speed increased. The optimum toughening effect was observed in PETG/POM blends compatibilized with polyether-based TPU at testing speed of 100 mm/min. The polyether-based TPU is a more efficient compatibilizer, because the amount required is one-half that of the polyester-based counterpart to achieve the same Kc value. This was attributed to the elastomeric nature of the polyether-based TPU. The softer nature of polyether-based TPU could provide better toughening effect than the polyester-based TPU, which is relatively harder in nature. POLYM. ENG. SCI., 45:710–719, 2005. © 2005 Society of Plastics Engineers
Degradation and polymerization of polyoxymethylene homopolymer (POM-H) surfaces after sliding at 8 to 150MPa and 0.005m/s
over a total sliding distance of 3000m is investigated by using thermal analysis (DSC, TGA, DTA) and Raman spectroscopy of
worn surfaces or wear debris. There is mainly mechanical interaction and slight softening at 8MPa (relatively high friction,
low wear), softening at 16 to 55MPa (decreasing friction and high wear) and finally melting at 150MPa (very low friction,
overload wear). At low contact pressures, wear debris remains amorphous and degradation of noncrystallised material during
sliding manifests in broadening of the melting peak below the melting temperature. Degradation of C–O–C due to chain scission
and radical reactions into CH3 end groups are illustrated by Raman spectra. It is confirmed that the debris has long resident times and the maximum polymer
surface temperature (T* = 93°C) is below the crystallisation temperature. At intermediate contact pressures, crystallisation results in a polymer
fraction with higher thermal resistance. From the calculated temperatures T* = 120 to 150°C, crystallisation is beneficial for coherent transfer with larger particle sizes. At high contact pressures,
the wear debris is immediately removed from the contact interface due to melting (T* = 200°C) and has thermal properties similar to the bulk material. There is no reaction between the debris in the interface,
resulting in a thick polymer transfer film.
Mechanical and physical properties of the blends of copolymer-type polyacetals (POM) with polyurethane (PU) were investigated. The properties relationships of POM/PU blends are established by studying their morphology and compatibility. For the blends rich in POM, the morphology of the blends observed with a scanning electron microscopy (SEM) indicates that the blends containing lower than 50 wt % (46 vol %) PU are almost completely filled with spherical particles of the dispersed PU. As the concentration of PU increases, the spherulites of the POM observed by SEM become less perfect with coarse fine structure. Furthermore, when the concentration of PU was increased up to 50 wt %, the spherulties of POM in the blends are smaller than those of unblended POM. X-ray diffraction studies reveal that the degree of crystallinity of POM decreases with increasing PU content, which is nonmonotonic. This conclusion agrees with the observations made by differential scanning calorimetry (DSC) and density measurements. For the blends rich in POM, mechanical properties show that the impact strength of POM/PU blends increased with decreasing spherical size of the dispersed PU.
Mechanical 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.
The formation of dispersed phase in blends of incompatible polymers during melt extrusion with a co-rotating twin screw extruder was studied, using nylon and polyester as the matrix and ethylene-propylene rubbers as the dispersed phase. A master curve is obtained, i.e., Gηm/ = 4p±0.84, where G is the shear rate, the particle diameter, η the interfacial tension, ηm the matrix viscosity, ηd the dispersed-drop viscosity, and p = ηd/ηm. The plus (+) sign applies for p > 1, and the minus (−) sign for p < 1. Thus, the dispersed-drop size is directly proportional to the interfacial tension and the ±0.84 power of viscosity ratio. The dispersed drops are the smaller, when the interfacial tension is the lower and the viscosity ratio is the closer to unity. The interfacial tension is largely controlled by the polarities of the two phases, and can be varied over several orders of magnitude by using appropriate dispersants.
Studies based on fracture mechanics have been made on polyacetal toughened with a synthesized thermoplastic polyurethane. The effects of elongation rate and defects like holes and notches on tensile properties have been investigated. Using three-point bending specimens, fracture mechanics parameters such as strain energy release rate, G, Rice's contour integral, J, and fracture toughness, K have also been determined under plain stress conditions. The mechanical loss from the hysteresis curves, and ductile, brittle fractography using scanning electron microscopy have also been studied.
Polyacetal (POM) toughening with thermoplastic polyurethane (TPU) elastomer was investigated in terms of Theological, mechanical, and morphological properties. Polyacetal can be effectively toughened by the blending with TPU elastomer and the improvement on toughness is found most significant with TPU content from 20 to 30 percent. POM does fracture in ductile mode under extremely low deformation rate and the ductile-brittle transition rate is at 0.5 mm/min. The transition rate is increased with the increase of elastomer content. The precrack hysteresis energy is important in dictating the failure mode. The experimental results show the hysteresis energy (under constant load) increases with the increase of elastomer content and the decrease of deformation rate. Greater hysteresis energy results in larger precrack plastic zone size and thus tends to shift the fracture mode from brittle to ductile as the critical size of the plastic zone is reached. The adoption of the slow rate fracture method has the advantages of ranking toughness of very brittle polymeric materials vs. the conventional Izod or Charpy impact method by varying temperatures. FTIR shows significant interaction between POM and TPU which is probably responsible for the TPU elastomer being such an efficient toughening agent for POM. Delamination in the buffer zone between the plane-strain and the plane-stress is discovered and the possible mechanism is discussed.
The effect of thermoplastic polyurethane (TPU) elastomer on the melting point and the percentage crystallinity of polyacetal (POM) is studied by differential scanning calorimetry (DSC). Wide angle X-ray diffraction (WAXD) scans of POM, TPU and their blends have been taken and the results indicate that the crystalline structure of POM remains unaffected even after the addition of amorphous TPU. The influence of defects like holes and notches on the ultimate tensile strength has been examined. The resistance to crack initiation (J
c), the resistance to steady state crack propagation (R
p) and the resistance to crack growth at maximum load (R
max) are estimated. The POM/TPU blends display higher crack resistance values than pure POM. The hysteresis energy of blends is determined and is found to increase with TPU content.