Study on the Thermal Stabilization Effect of Polyamide on Polyoxymethylene

The thermal stabilization effect of polyamide (PA) on polyoxymethylene (POM) was studied by the isothermal weight loss analysis and thermogravimetric analysis (TGA), which shows that with the increase of PA content, the thermal weight loss and degradation rate decrease, the characteristic thermal degradation temperatures increase, and the thermal stability of POM can be improved remarkably. The nonisothermal degradation kinetics evaluated from TGA by the Coats-Redfern method shows that the PA-modified POM has higher activation energy than the virgin POM. The yellow index (YI), the melt index (MI), and the mechanical property measurements for both the virgin and the modified POM by multiple-processing further demonstrate that the PA applied in this study shows remarkable thermal stabilization effect on POM.     

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.     

Study on the High Efficiency Antioxidant of Polyoxymethylene

This article reports on the properties and uses of antioxidant F/B, a type of high efficiency antioxidant for polyoxymethylene (POM), consisting of the hindered phenolic main antioxidant, the secondary thermostabilizer phosphite ester, and lactone compound. Our experimental studies focused on the thermostabilization effect of antioxidant F/B on POM, which was measured by isothermal weight loss analysis at 220°C, isothermal weight loss rate analysis at 222°C, balance torque analysis, nonisothermal gravity analysis (TGA), oxidation induction time (OIT) analysis, and multiple processing and long-term aging analysis as compared to the commonly used antioxidant Irganox245 of POM. The results showed that the thermal stability of POM can be improved remarkably by using antioxidant F/B. The aging mechanism of POM under heat and oxygen was studied by the measurements of polarized light microscopy (PLM), differential scanning calorimetry (DSC), and X-ray photoelectron energy spectrum (XPS), which showed very slight changes of spherulites dimension, crystallinity, and the surface atom concentration after 15 days of aging at 140°C. Furthermore, the small amount of degradation of POM only occurred in the amorphous region of POM. These experiments demonstrated that lower amounts of antioxidant F/B can reach the same level of thermal stabilization of POM as is achieved with higher amounts of Irganox245, and can replace Irganox245 for use in the production of POM, which can further improve the thermal stabilization and reduce the production cost of POM.     

Nucleation effect of polyamide on polyoxymethylene

The crystallization behavior and morphology of polyoxymethylene (POM) and POM with polyamide (PA) were studied by polarized light microscopy (PLM), isothermal and nonisothermal differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The isothermal crystallization kinetics were analyzed with the Avrami equation. Compared with the virgin POM, the addition of PA can reduce the spherulites size and improve the crystallization growth rate and crystallinity (X_c) of POM, which demonstrates that the nucleation effect of PA as the high‐molecular nucleus is favorable to the mechanical properties and dimension stability of POLYM. ENG. SCI., 45:1174–1179, 2005. © 2005 Society of Plastics Engineers     

复配型受阻酚类抗氧剂对聚甲醛的稳定作用

将受阻酚类抗氧剂Irganox245和Irganox1010进行复配并加入聚甲醛中，通过将物料在设定温度下多次挤出，测定挤出物料的黄色指数、拉伸强度、冲击强度、熔体质量流动速率、热失重率等方法对单剂和复配抗氧剂在聚甲醛中的稳定作用进行了研究。结果表明：将抗氧剂Irganox245和Irganox1010复配后，提高了聚甲醛的分解温度，较好地保持了聚甲醛的各项性能，没有发生劣化现象，作用效果介于两种抗氧剂单独作用效果之间；在聚甲醛的热氧稳定性能方面起到一定的协同作用。     

无卤膨胀阻燃PP/PA6合金性能研究

研究了以聚磷酸铵（APP）、三聚氰胺（MA）和层状复合金属氢氧化物（LDH）复配得到的膨胀阻燃剂（IFR）对聚丙烯／尼龙6（PP／PA6）合金性能的影响，分析了不同阻燃体系对PP／PA6合金的阻燃性能、力学性能、热性能和微观形态的影响。结果表明，当APP／MA／LDH为21．0／7．5／1．5（质量比）时，PP／PA6合金具有较好的阻燃性能并能保持较高的力学性能。LDH可以提高阻燃材料的热稳定性和残炭量，而且SEM照片显示炭层微观形态为“面包”状的膨松状。     

Studies on novel composites of polyoxymethylene/ polyamide 6

A series of new composite of polyoxymethylene/polyamide 6 (POM/PA 6) were synthesized by using ε‐caprolactam as a reactive solvent with POM soluble in it. Incorporating a small content of POM (1–4 wt %) into PA 6 led to a great improvement of impact resistance POM/PA 6. The effects of POM content on the mechanical, morphological, and thermal properties of the composites were investigated. Incorporating minor POM (1 wt %), disposed in finely dispersed level (about 1 μm), into PA 6 matrix can greatly reduce the crystallization rate and crystallinity of PA 6. Scanning electron microscopy measurements indicated that much microfibers with aspect ratio about 10 appeared with the addition of 3 wt % POM because of the change of phase separation mechanisms. As a result, with a small content of PA 66 (1–4 wt %) incorporated, the impact strength and elongation of POM/PA 6 were improved markedly, with retention of good tensile strength. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 335–339, 2006     

High Efficiency Nucleating Agents of Polyoxymethylene

In this research, the effects of different kinds of nucleating agents on the crystallization and mechanical properties of polyoxymethylene (POM) were studied, including inorganic, organic, and polymer nucleating agents and their compounds. These properties showed that nanoCaCO₃, sorbitol derivative TMB-5, polyamide PA-4, and compound C-1/polyamide (PA)-4 can make spherulites of POM finer and more perfect, and effectively improve its notched impact toughness, in which the compound C-1/PA-4 displayed more remarkable nucleation effect. The study on the nonisothermal crystallization of POM showed that the crystallization temperature and crystallization growth rate of POM increased when C-1/PA-4 was added. The isothermal crystallization kinetics were also analyzed by the Avrami equation. The addition of C-1/PA-4 can increase the values of the Avrami exponent (n) and crystallization rate constant (k), and reduce the half-time of isothermal crystallization, t_1/2, and the time corresponding to the maximum rate of crystallization, t_P, indicating its remarkable nucleating effect on POM.     

Thermal stabilization effect of biphenol monoacrylate on polyamide 6

Biphenol monoacrylate (AL) was combined with a traditional hindered phenolic‐based binary antioxidant system to form a ternary stabilization system for the purpose of further improving the thermal–oxidative stability of polyamide 6 (PA6). The thermal stabilization effect of the antioxidant AL on PA6 was studied in terms of the reduced viscosity, the chemical structure, the yellow index, and the mechanical properties. The results showed that the antioxidant AL, with the proper chemical structure, could improve the thermal stability of PA6 effectively through a unique bifunctional stabilizing mechanism. The interaction of the molecules of PA6 with the antioxidant AL was investigated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nonisothermal crystallization kinetics of polyoxymethylene/montmorillonite nanocomposite

The nonisothermal crystallization kinetics of polyoxymethylene (POM), polyoxymethylene/Na–montmorillonite (POM/Na–MMT), and polyoxymethylene/organic–montmorillonite (POM/organ–MMT) nanocomposites were investigated by differential scanning calorimetry at various cooling rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the nonisothermal crystallization process of POM/Na–MMT and POM/organ–MMT nanocomposites. The difference in the values of the exponent n between POM and POM/montmorillonite nanocomposites suggests that the nonisothermal crystallization of POM/Na–MMT and POM/organ–MMT nanocomposites corresponds to a tridimensional growth with heterogeneous nucleation. The values of half‐time and the parameter Z_c, which characterizes the kinetics of nonisothermal crystallization, show that the crystallization rate of either POM/Na–MMT or POM/organ–MMT nanocomposite is faster than that of virgin POM at a given cooling rate. The activation energies were evaluated by the Kissinger method and were 387.0, 330.3, and 328.6 kJ/mol for the nonisothermal crystallization of POM, POM/Na–MMT nanocomposite, and POM/organ–MMT nanocomposite, respectively. POM/montmorillonite nanocomposite can be as easily fabricated as the original polyoxymethylene, considering that the addition of montmorillonite, either Na–montmorillonite or organ–montmorillonite, may accelerate the overall nonisothermal crystallization process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2281–2289, 2001     

Synergistic effects of ammonium polyphosphate/melamine intumescent system with macromolecular char former in flame-retarding polyoxymethylene

The improvement of the flame retardancy of polyoxymethylene (POM) is a world-wide difficult problem due to its zippered decomposition property. This paper reported the preparation of the flame-retarding (FR) POM with the synergistic combination of ammonium polyphosphate (APP)/melamine (ME) intumescent flame retardant system and macromolecular char former (MC). The UL94 testing, mechanical properties testing, thermogravimetric analysis (TGA), cone calorimetry and scanning electron microscopy (SEM) were used to investigate the corresponding structure, performance and synergistic flame retardant mechanism. The experimental results showed that, in the used macromolecular char formers (novolac, PA6 and TPU), the combination of novolac with APP/ME intumescent system has the best synergism in flame-retarding POM, greatly enhancing the quality of the formed condensed charred layer and hence the corresponding flame retardancy. The obtained FR POM composite could achieve flame retardancy of UL94 3.2 mm V-0 level and remarkably decreased heat release rate relative to pure POM. The synergistic effect of novolac was shown to be the char formed cross-linking reaction of it with APP. Due to the thermodynamic compatibility of novolac and POM, the prepared FR POM composite also has fairly good mechanical performance, having tensile strength of 49.1 MPa and Izod notched impact strength of 2.60 kJ/m².     

高分子甲醛吸收剂对聚甲醛的热稳定性能与结构的影响研究

采用差式扫描量热仪、热重分析仪及偏光显微镜研究高分子甲醛吸收剂共聚酰胺(COPA)和密胺树脂(MF)对聚甲醛(POM)的热稳定性能与结构的影响。结果表明,两种高分子甲醛吸收剂都能起到结晶成核剂的作用。同时,COPA对POM的热稳定性效果要优于MF,但会提高POM的黄色指数,而MF会降低POM的黄色指数。     

Melting behavior and nonisothermal crystallization kinetics of polyamide 6/polyamide 66 molecular composites via in situ polymerization

The melting behavior and nonisothermal crystallization kinetics of pure polyamide 6 (PA 6) and its molecular composites with polyamide 66 (PA 66) were investigated with differential scanning calorimetry. The PA 6/PA 66 composites had one melting peak, whereas the coextruded PA 6/PA 66 blends had two melting peaks. With the addition of PA 66 to PA 6 via in situ anionic polymerization, the melting temperature, crystallization temperature, and crystallinity of PA 6 in the composites decreased. The half‐time of nonisothermal crystallization increased for a PA 6/PA 66 molecular composite containing 12 wt % PA 66, in comparison with that of pure PA 6. The commonly used Ozawa equation was used to fit the nonisothermal crystallization of pure PA 6 and its composites. The Ozawa exponent values in the primary stage were equal to 1.28–3.03 and 1.28–2.97 for PA 6 and its composite with 12 wt % PA 66, respectively, and this revealed that the mechanism of primary crystallization of PA 6 and PA 6/PA 66 was mainly heterogeneous nucleation and growth. All the results indicated that the incorporation of PA 66 into PA 6 at the molecular level retarded the crystallization of PA 6. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2172–2177, 2005     

Nonisothermal crystallization kinetics of flame‐sprayed polyamide 1010/nano‐ZrO2 composite coatings

Polyamide1010 (PA1010) and its composite with nanometer‐sized zirconia (PA1010/nano‐ZrO₂) coatings were deposited using a flame spray process. The kinetics of nonisothermal crystallization of PA1010/nano‐ZrO₂ composite coatings was investigated by differential scanning calorimetry (DSC) at various cooling rates. Several different analysis methods were used to describe the process of nonisothermal crystallization. The results showed that the modified Avrami equation and Mo's treatment could describe the nonisothermal crystallization of the composite coatings very well. The nano‐ZrO₂ particles have a remarkable heterogeneous nucleation effect in the PA1010 matrix. The values of halftime and Z_c showed that the crystallization rate increased with increasing cooling rates for both PA1010 and PA1010/nano‐ZrO₂ composite coating, but the crystallization rate of PA1010/nano‐ZrO₂ composite coating was faster than that of PA1010 at given cooling rate. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

凝胶丁腈共聚弹性体增韧聚甲醛的加工流变行为及力学性能

研究了聚甲醛(POM)/凝胶丁腈共聚弹性体(GNBE)共混物的熔体流动指数(MFI)、高压毛细管流变行为和力学性能。结果表明,共混物MFI随GNBE用量的增加下降较大。聚酰胺(PA)对POM/GNBE共混体系的MFI影响较小,而热塑性酚醛树脂(PFR)的影响显著。当PFR的质量份为4时,POM共混物的MFI达最小值(0.053g/min),约为未加增容剂POM共混物MFI的1/6。随着剪切速率的提高,共混物剪切黏度迅速与POM接近。这种黏度变化行为说明共混物比GNBE对剪切速率更敏感,共混物的黏度受POM的影响较大。随着剪切速率的提高,POM与GNBE的黏度比迅速减小,并接近1,说明POM和GNBE在高剪切速率下共混时,GNBE的液滴能够在POM连续相中分散达到最小。含20份GNBE的POM共混物在高剪切速率下的熔体表观黏度与POM相当;在PFR质量份为6时,POM共混物的缺口冲击强度达到21.6kJ/m2,超过了GNBE质量份为40的POM共混物。当PFR质量份为4时,共混物的缺口冲击强度为对应的不加增容剂共混物的冲击强度的2倍多,扯断伸长率提高了55.4%。     

阻燃成炭剂trimer和微胶囊红磷复配阻燃聚甲醛的研究

采用兼具阻燃和成炭作用的笼状磷酸酯三（1-氧代-1-磷杂-2,6,7-三氧杂双环［2.2.2］辛烷-4-亚甲基磷酸酯）（trimer）和微胶囊红磷（MRP）复配阻燃聚甲醛（POM）。采用垂直燃烧试验、极限氧指数和热重分析研究复配阻燃体系对POM的阻燃性能,并对阻燃POM的力学性能进行分析。结果表明,trimer和MRP有很好的协同阻燃性能;trimer/MRP/ME的添加量为23 %时,阻燃聚甲醛达到UL 94 V-0,极限氧指数最高达29.4 %。     

Enhancement of thermal,morphological, and mechanical properties of compatibilized based on PA6-enriched graphene oxide/EPDM-g-MA/CR: Graphene oxide and EPDM-g-MA compatibilizer role

In this study, a series of elastomeric nanocomposites based on specific amounts of polyamide6 (PA6)/chloroprene rubber (CR) blends which are compatibilized with ethylene propylene diene monomer-grafted-maleic anhydride (EPDM-g-MA) and different amounts of graphene oxide (GO) were prepared with melt mixing method. The effect of compatibilizer and reinforcement concentration in the PA6/CR blend matrix was investigated using theoretical and experimental analysis. Dispersion of nanoplatelets within rubber blend matrix was proven with transmission electron microscopy and field emission-scanning electron microscopy. The modified microstructure of samples showed the significant effect of EPDM-g-MA and GO on the size reduction of CR droplets in the PA6 continuous phase. The results from differential scanning calorimetry and dynamic mechanical thermal analysis revealed the effect of EPDM-g-MA and GO as an effective nucleating agent in PA6-enriched GO/CR (PA6EGO/CR). The findings obtained from thermogravimetric analysis displayed that the GO in the presence of an EPDM-g-MA as a compatibilizer can cause a higher thermal stability in PA6EGO/CR. From mechanical properties, by adding a compatibilizer to the PA6/CR blend, the tensile strength changed from 39.0 to 45.1, the Young's modulus altered from 522.2 to 716.0 and the elongation at break changed from 246.8 to 222.2. While incorporation of 5 phr of GO to the compatibilized blend, the tensile strength increased by 25.2%, the Young's modulus increased by 36.6% and the elongation at break decreased by 20%. The Christensen–Lo model used for analyzing the stiffness of PA6EGO/EPDM-g-MA/CR with emphasis on the influence of the interphase region to predict the effect of various loadings of GO and EPDM-g-MA of Young's modulus. The rheology and creep tests showed a significant effect of EPDM-g-MA and GO content on the rheology behavior of nanocomposites.     

Crystallization behavior of polyamide 11/multiwalled carbon nanotube composites

Differential scanning calorimetry (DSC) was used to investigate the isothermal and nonisothermal crystallization kinetics of polyamide11 (PA11)/multiwalled carbon nanotube (MWNTs) composites. The Avrami equation was used for describing the isothermal crystallization behavior of neat PA11 and its nanocomposites. For nonisothermal studies, the Avrami model, the Ozawa model, and the method combining the Avrami and Ozawa theories were employed. It was found that the Avrami exponent n decreased with the addition of MWNTs during the isothermal crystallization, indicating that the MWNTs accelerated the crystallization process as nucleating agent. The kinetic analysis of nonisothermal crystallization process showed that the presence of carbon nanotubes hindered the mobility of polymer chain segments and dominated the nonisothermal crystallization process. The MWNTs played two competing roles on the crystallization of PA11 nanocomposites: on the one hand, the MWNTs serve as heterogeneous nucleating agent promoting the crystallization process of PA11; on the other hand, the MWNTs hinder the mobility of the polymer chains thus retarding the crystal growth process of PA11. The activation energies of PA11/MWNTs composites for the isothermal and nonisothermal crystallization are lower than neat PA11. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Thermal stability and thermal degradation kinetics of short and long glass fiber reinforced PA10T composites

In this work, the long glass fiber reinforced poly(decamethylene terephthalanide) (PA10T/LGF) composites and short glass fiber reinforced PA10T (PA10T/SGF) composites were prepared by two different extrusion processing methods, respectively. The results of mechanical properties reveal the introduction of glass fiber can improve the performance of the material, and the LGF reinforced PA10T composites can achieve much higher performance than the SGF reinforced ones at the same level of fiber contents. The thermal stabilities of neat PA10T, PA10T/SGF, and PA10T/LGF are investigated by nonisothermal TG analysis. The thermal degradation kinetics is introduced by using Kissinger and Flynn‐Wall‐Ozawa methods and the thermal degradation mechanism functions of the samples are calculated by the Coats‐Redfem model. The results show that the thermal stabilities of PA10T/SGF and neat PA10T are better than that of PA10T/LGF. In addition, the incorporation of glass fiber into PA10T do not have much effect on the reaction mechanism type of thermal degradation compared with that neat PA10T. Furthermore, the thermal stability analysis of the composites is verified by the computed results of Gibbs free energy (ΔG^#). POLYM. ENG. SCI., 59:246–253, 2019. © 2018 Society of Plastics Engineers     

Studies on crystallization behaviors and crystal morphology of polyamide 66/clay nanocomposites

X‐ray diffraction methods, DSC thermal analysis, and polarized light microscopy (PLM) were used to investigate the structural changes of nylon 66/clay nanocomposites. PA 66/clay nanocomposites were prepared by the method of melt intercalation. The results indicate that the addition of the intercalated organo‐montmorillonite (OMMT) can induce generation of the β‐form crystal of PA 66 and substantially affect the arrangement of molecules in the α‐form crystal, although the crystallinity scarcely changes. Also, the DSC results indicate that the addition of OMMT in the PA 66 matrix leads to increases of crystallization temperatures and the full width at half maximum (FWHM) of the exothermic peaks. Moreover, the viscosity factor is the main influence on FWHM of the exothermic peaks of PA 66/clay nanocomposites. The results of nonisothermal crystallization kinetics show that OMMT has the effect of heterogeneous nucleation and leads to the decrease of the size of the spherocrystal. The heterogeneous nucleation effects of OMMTs influence the mechanism of crystallization and the growth mode of PA 66 crystals. PLM photographs verify that the size of spherocrystal is decreased and visually confirm the theory of crystallization kinetics. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 756–763, 2005