Enhancement in Thermal Stability of Polyoxymethylene (POM)-Based Biopolymer Blend Materials

In this study, we demonstrate the enhancement in thermal stability of polyoxymethylene (POM)-based biopolymer blend materials. Polyoxymethylene (POM)/Polylactic acid (PLA) blends have been used as alternative biopolymer materials for supporting environmental problems with thermal stability feature. The effects on POM biopolymer blend materials with a controlled PLA amount in their compositions under various injection conditions, were investigated by thermogravimetric analysis, dynamic mechanical analysis, and differential scanning calorimetry. The POM/PLA biopolymer blend materials showed POM phase acted as a homogeneous nucleating site for increasing PLA crystallization, which improves storage modulus of the blend materials. The decomposition temperatures of POM/PLA biopolymer blends tend to shift around 30˚C - 50˚C lower compared to the decomposition temperatures of PLA. Thus, the decomposition temperature behavior of POM/PLA blends seems to be closer to POM. The suitable ratio in POM70/PLA30 resulted in the high strength of the blend materials. The POM/PLA biopolymer blend material was tested at various injection speeds and good miscibility was obtained at an injection speed of 100 mm/s. This enhancement of thermal stability in POM/PLA blend materials should be useful in the development of high-performance bio-based thermoplastic materials.

Studies on polyoxymethylene dimethyl ethers production from dimethoxymethane and 1,3,5-trioxane over SO_(4)^(2-)/ZrO_(2)-TiO_(2)

Polyoxymethylene dimethyl ethers(OMEs)with physical properties similar to those of diesel has received significant attention as green additives for soot emission suppression.Herein,series of SO_(4)^(2-)/ZrO_(2)-TiO_(2)catalysts were developed for OMEs production from dimethoxymethane(DMM)and1,3,5-trioxane through sequential formaldehyde monomer insertion into C-O bond of DMM.Not Lewis but Bronsted acid sites were identified to be active for the decomposition of 1,3,5-trioxane into formaldehyde unit,however,both of them are effective for the chain propagation of DMM via formaldehyde unit insertion into C-O bond.Kinetic studies indicated each chain growth step exhibited the same parameters and activation barrier on corresponding Bronsted and Lewis acid sites due to the same reaction mechanism and very similar chemical structure of OMEs.Also,the catalytic stability investigation suggested the deactivation behavior was derived from the carbon deposition,and the decay factor could be exponentially correlated with the amount of coke accumulation.

基于POM的全球M_(2)正压潮数值模拟

普林斯顿海洋模型(POM)是应用较为广泛的区域海洋数值模型,但在全球潮汐数值模拟中的适用性尚待检验。本研究将三极网格和潮汐势引入POM中,对包含北极点的海洋潮波问题进行模拟,并建立水平分辨率1°×1°的全球大洋潮波数值模型,对全球M_(2)正压潮波进行数值模拟。模拟结果显示,太平洋存在5个M_(2)分潮无潮点,大西洋存在4个M_(2)分潮无潮点,印度洋存在3个M_(2)分潮无潮点,北冰洋存在2个M_(2)分潮无潮点;总体来看,大洋M_(2)分潮振幅小于近岸振幅,赤道太平洋海域出现2个M_(2)分潮的高振幅区,北冰洋与其他三大洋相比振幅最小。POM模拟结果与TPXO7.2全球潮汐同化模型结果基本一致,两者振幅均方根误差为5.6 cm,迟角均方根误差为10.0°,振幅的平均相对误差为12.5%;POM模拟结果与全球潮汐常数(GTCs)数据集对比,两者振幅均方根误差为21.4 cm,迟角的均方根误差为29.1°,振幅的平均相对误差为25.1%。表明所构建的POM全球大洋潮波模型能够较为准确地模拟全球潮波,得到全球潮汐的分布特征,为POM应用于其他全球海洋动力过程研究提供借鉴和参考。

POM/PP/PE高刚耐热复合材料的制备及性能研究

为获得高刚耐热聚乙烯基复合材料用于工程结构的改善和优化,本文制备了聚甲醛(POM)/聚丙烯(PP)/聚乙烯(PE)三元复合材料。采用PE-g-MAH作相容剂改善POM/PP/PE三元体系的相容性,研究PE-g-MAH对POM/PP/PE复合材料性能的影响。当PE-g-MAH添加量达到7.5份时,复合材料屈服强度达到最大值24.76MPa,提升了15.4%;冲击强度达到最大值25.78kJ·m^(-2),提升了50.7%;屈服伸长率达到最小值13.96%,降低了29.3%。结果表明,PE-g-MAH的加入提高了POM/PP/PE复合材料的综合力学性能,既改善了材料的相容性,同时也大幅提高了复合材料的储能模量,材料的刚性和耐热性能均得到了改善。

基于多指标下POM纤维对EPS轻型混凝土性能的影响

为探究聚甲醛(POM)纤维对聚苯乙烯(EPS)轻型混凝土性能的综合影响,避免以往单纯依赖力学性能指标评价的不足,比选后基于长度为12 mm的POM纤维研究了不同性能评价指标下POM纤维的最优掺量。结果表明:基于基本的力学性能及相对动弹性模量变化绝对值,掺量为0.9%时,POM纤维对EPS轻型混凝土的增强效果最优,冻融损伤最低;基于吸水性及流变性能指标,掺量同样为0.9%时浆体稠度及抗吸水能力最佳;基于干缩性能,则掺量为1.2%时,浆体抗干缩效果最优;基于冻融后相对弹性模量变化率,则掺量为0.6%时相对弹性模量衰减率最低;研究揭示了POM纤维增强EPS轻型混凝土的复杂性和多样性,进一步通过微观分析,辅证了POM纤维增强增韧EPS轻型混凝土的机理。

FVCOM与POM在黄渤海潮波数值模拟的对比研究

FVCOM与POM是在中国海域应用较为普遍的两种海洋模型,两种模型的网格划分方式不同,FVCOM采用非结构化网格,POM采用结构化网格。利用黄渤海沿岸共37个验潮站的资料对模拟结果进行验证对比,并结合前人的研究,发现FVCOM与POM均能较好地模拟黄渤海海域的潮波系统,两者的数值模拟结果相似,但也有不同。将FVCOM与POM两种海洋模型计算结果与37个验潮站实测数据调和分析出的M2分潮振幅和迟角进行拟合对比分析,表明FVCOM模式在黄渤海海域潮汐模拟的效果要优于POM模式。

Mechanism of chain propagation for the synthesis of polyoxymethylene dimethyl ethers

Polyoxymethylene dimethyl ethers(PODE)were synthesized from the reaction of paraformaldehyde with dimethoxymethane(DMM)over different acid catalysts at different conditions.Products were found to follow the Schulz-Flory distribution law.The chain propagation proceeds through the insertion of an individual segment of CH2O one by one,while the simultaneous insertion of a few CH2O segments or their assembly is unlikely.Due to the restriction of this law,it is difficult to increase the selectivity to the desired products(e.g.,PODE3 4).

Chemical equilibrium controlled synthesis of polyoxymethylene dimethyl ethers over sulfated titania

The chemical equilibrium and reaction kinetic behavior in the synthesis of polyoxymethylene dimethyl ethers （DMMn） were investigated over sulfated titania in order to reveal the decisive factor controlling the reaction. The results showed that the molar ratio of adjacent DMMn products in equilibrium solution had the same value, which depended absolutely on the reaction temperature. Meanwhile, the reactions had the same DMMn products distributions under varied reaction conditions. The equilibrium constants of the related step-wise reactions for DMMn formation were equal, which were calculated based on the bulk compositions of the reaction solution. And thus, the selectivity to DMMn was mainly controlled by the chemical equilibrium, i.e., thermodynamic control. In brief, the present results provide some guidance for future synthesis of DMMn.

A Synthesis, Process Optimization, and Mechanism Investigation for the Formation of Polyoxymethylene Dimethyl Ethers

Polyoxymethylene dimethyl ethers(DMM_n) are promising diesel additives. The synthesis of DMM_n from methylal(DMM) and paraformaldehyde over the NKC-9 acidic ion-exchange resin catalyst was investigated. Many unrecyclable by-products such as methyl formate, dimethyl ether and formic acid were produced in the reaction. To increase the selectivity of the desired products DMM_(3-6) and reduce the amount of unrecyclable by-products, the effects of reaction temperature, time, pressure and the molar ratio of the raw materials were evaluated through a series of single factor experiments. Experiments revealed that trace amount of water could suppress the formation of unrecyclable by-products, and the optimum initial water content(less than 2 wt%) was investigated. In addition, the synthetic process needs to go through the polyoxymethylene hemiformals intermediate stage, and then the DMM_n were obtained when polyoxymethylene hemiformals reacted with methanol. Ultimately, a possible mechanism is proposed to describe the formation of DMM_n from polyoxymethylene hemiformals in detail, in which it is revealed that the formation of carbocation intermediates is important in the reaction processes.

基于3POM教育模式的实践创新型研究生人才培养途径

研究生实践创新能力的培养是高校教育教学改革的重要内容。本研究对研究生创新实践能力培养模式进行了探究。三维系统植物次生代谢教学模式(3POM)在传统课堂授课的基础上,充分利用互联网教育平台的各种优势,增添了“海报制作”“论坛汇报”2个模块,形成了完整的知识转化体系,对实践创新型研究生人才的培养具有积极意义,同时可以汇集社会资源,打破传统教育资源局限,为研究生科研素养与创新能力提升的教学模式改革提供了思路。

The Friction Wear Properties and Application of Thermoplastic Polyester Elastomer and Polyoxymethylene

The experiment of injection molding, Dais-simulating test, morphological structure investigation(Scanning Electron Microscopy, SEM),X-ray photoelectron spectroscopy(XPS)were performed on mini-automobile spherical seat which was made of thermoplastic polyester elastomer(TPEE)and oiled polyoxymethylene(POM),respectively. The friction-wear properties between the frictionl pair of polymer spherical seat and metallic(iron)spherical pin were studied. The test results indicate that the antifriction property of TPEE is superior to that of POM, while its surface chemical effect is inferior to that of POM.

Study on the Miscibility and Phase Behavior of Polyoxymethylene with Novolak

The miscibility and phase behavior of the blends of polyoxymethylene (POM)/Novolak were investigated by the cloud point method, which showed that the POM/Novolak blends exhibited a lower critical solution temperature. The melting point of POM decreased when diluted with Novolak. From the melting temperature depression of POM, a negative interaction parameter (x) between POM and Novolak was obtained. The IR spectrum revealed that the miscibility between POM and Novolak was caused by the specific interaction between the OH groups of Novolak and the ether oxygen atoms of POM. The morphology of the blends investigated by polarized light microscopy showed that the size of spherulites of POM was sharply decreased by its mixing with Novolak. This suggests that Novolak be used as a compatibilizer for POM.

Brφsted-acidic ionic liquids as efficient catalysts for the synthesis of polyoxymethylene dialkyl ethers

Acetalation of formaldehyde(HCHO)with dialkyl formal or aliphatic alcohol to prepare polyoxymethylene dialkyl ethers(RO(CH2O)nR,n≥1)catalyzed by Br?nsted‐acidic ionic liquids has been developed.The correlation between the structure and acidity activity of various ionic liquids was studied.Among the ionic liquids investigated,1‐(4‐sulfonic acid)butyl‐3‐methylimidazolium hydrogen sulfate([MIMBs]HSO4)exhibited the best catalytic performance in the reaction of diethoxymethane(DEM1)with trioxane.The influences of ionic liquid loading,molar ratio of DEM1to HCHO,reaction temperature,pressure,time,and reactant source on the catalytic reaction were explored using[MIMBs]HSO4as the catalyst.Under the optimal conditions of n([MIMBs]HSO4):n(DEM1):n(HCHO)=1:80:80,140°C,and4h,the conversion of HCHO and selectivity for DEM2?8were92.6%and95.1%,respectively.The[MIMBs]HSO4catalyst could be easily separated and reused.A feasible mechanism for the catalytic performance of[MIMBs]HSO4was proposed.

Controllable synthesis of polyoxymethylene dimethyl ethers by ionic liquids encapsulated in mesoporous SBA-16

The promising combustion and emission properties of polyoxymethylene dimethyl ethers(PODEn)are of significant interest.However,the synthesis of PODEn products with desired chain lengths is still a problem facing synthetic PODEn.Herein,a series of unique IL@SBA16Cx solid catalysts are prepared by encapsulation of ionic liquids(ILs)within the nanocage of SBA16 through a silylation method.The structure of the encapsulated catalyst was characterized by UVvis spectra,Fourier transform infrared(FTIR),N2 adsorptiondesorption isotherms,Powder Xray diffraction(XRD),Transmission electron microscopy(TEM)and Elemental analysis.The encapsulated catalysts show similar catalytic activity to the homogeneous counterparts and display higher selectivity to the targeted PODE35 products than their homogeneous counterparts in the synthesis of PODEn from methanol(MeOH)and trioxymethylene(TOM).The encapsulated catalysts exhibit a superior PODE35 selectivity and could be the promising catalysts for PODEn synthetic reaction.

POM圆盘轴对称弯曲振动研究

研究了一种材料为聚甲醛(POM)的薄圆盘声波辐射体,压电换能器在其中心处产生振动激励.采用解析法设计了POM圆盘,用有限元方法对POM圆盘−换能器振动系统进行了建模、计算.在系统谐振频率处,有限元计算和实验测试了圆盘的振动位移与系统的电声效率.结果表明,POM圆盘和钢圆盘半径、厚度相同时,POM圆盘−换能器振动系统在空气中的半功率带宽更宽,而钢圆盘−换能器振动系统的电声效率更高;POM圆盘−换能器振动系统更易施加较高的电压或有功功率;激励电压相同时,POM圆盘的振动位移大于钢圆盘.

Investigation of the Thermal Decomposition Properties of Polyoxymethylene

By testing the melt index （MI）, tensile strength and breaking extension ratio, the thermal ageing rate of polyoxymethylene （POM） was analyzed and compared. The surface morphology and type of function group of POM surface were observed and analyzed by SEM and XPS. The results show that the MI value increases gradually with the ageing time at 120℃, indicating that the thermal oxidation decomposition occurrs slowly. The effect of 20-day thermal ageing on the tensile strength and breaking extension ratio of POM is not obvious, showing that the ageing of POM is quite a long process. After 105-day, thermal ageing cracking and powdering occurr on the POM surface. XPS determination shows the Cls spectra of samples before and after ageing include two peaks of C-C and C-O, while after ageing the content of C-C decreases and the content of C-O increases, indicating that the thermal ageing of POM is mainly the breaking and decomposing of C-C bond. The Ols/Cls ratio of original samples is 56.98% and after 105-day thermal ageing the ratio is 72.92%.

Formation kinetics of polyoxymethylene dimethyl ethers from methylal and trioxane with little water

Polyoxymethylene dimethyl ethers(CH_(3)-O-(CH_(2)O)_(n)-CH_(3),PODE_(n),n>1)can be added to diesel to reduce air pollution caused by incomplete combustion.Driven by this need,a cost-effective and efficient synthetic route is presented and investigated by this work for the production of PODE_(n),which are formed from methylal and trioxane with low water content(<10%(mass))over HZSM-5 catalyst in a batch slurry autoclave at the temperature from 353.15 K to 393.15 K.The reaction rate laws including the PODE_(n) and byproducts of polyoxymethylene hemiformals(HF_(n)),polyoxymethylene glycols(MG),methanol(MeOH)and methyl formate(MF)are developed.The rate constants of propagation step(k_(6))and depolymerization step(k_(-6))are assumed independent on polymerization degree of PODE_(n).The rate of reaction is proportional to the content of the catalyst(Wcat)for the catalytic reaction within the scope of the study.All kinetic parameters were estimated by combining genetic algorithm and least square regression to fit experimental data well.This work is valuable for process optimization and reactor design.

Mechanical and Morphological Properties of Polypropylene/Polyoxymethylene Blends

This work studies the mechanical and morphological properties of polypropylene (PP)/polyoxymethylene (POM) blends. The PP/POM blends were prepared by melting-blend with an internal mixer. The contents of PP were used at 10%, 20%, 30%, 70%, 80% and 90% by weight. The phase morphology of the blends was observed by scanning electron microscope (SEM) due to the mechanical properties depended on the phase morphology. The results show the decrease of the impact strength, Young’s modulus and tensile strength of POM/PP blends with increasing of PP content up to 30 wt% and then increase again with a high PP content. The percent strain at break of the blends increases after adding PP in a range of 70 - 90 wt%. SEM study reveals that the POM/PP blends clearly demonstrate a two-phase matrix-particle microstructure. The results also show that the domain size of dispersed PP or POM phase increases with increasing PP or POM content. The POM domain size is smaller than the PP domain size which leads to a little change of mechanical results of PP.

eXtended Pom-Pom黏弹性流体的改进光滑粒子动力学模拟

黏弹性流体广泛存在于自然界和工业生产中,对其复杂流变特性的研究具有重要的学术价值和应用意义.本文提出一种改进的光滑粒子动力学方法,对基于eXtended Pom-Pom模型的黏弹性流动进行了数值模拟.为了提高计算精度,采用一种不含核导数计算的核梯度修正离散格式.为了防止粒子穿透固壁,提出一种增强型的边界处理技术.为了消除张力不稳定性,将人工应力耦合到动量守恒方程中.运用改进光滑粒子动力学方法数值模拟了基于eXtended Pom-Pom模型的黏弹性Poiseuille流和黏弹性液滴撞击固壁问题,通过与解析解或有限差分方法解的比较以及对数值收敛性的评价,验证了改进光滑粒子动力学方法的有效性和优势,并在此基础上,深入分析了Reyonlds数、Weissenberg数、溶剂黏度比、各向异性参数、松弛时间比和分子链臂数等流变参数对流动过程的影响.

Polyoxymethylene dimethyl ethers synthesis from methanol and formaldehyde solution over one-pot synthesized spherical mesoporous sulfated zirconia

The synthesis of polyoxymethylene dimethyl ethers as an ideal diesel fuel additive is the current hot topic of modern petrochemical industry for their expedient properties in mitigating air pollutants emission during combustion.In this work,a series of spherical sulfated zirconia catalysts were prepared by a one-pot hydrothermal method assisted with surfactant cetyltrimethylammonium bromide(CTAB).The prepared sulfated zirconia catalysts were used to catalyze PODEn synthesis from methanol and formaldehyde solution.Various characterization(XRD,BET,SEM,TGA,NH_(3)-TPD,FTIR,and Py-IR)were employed to elaborate the structure–activity relationship of the studied catalytic system.The results demonstrated that S/Zr molar ratio in precursor solution played an effective role on catalyst morphology and acidic properties,where the weak Brønsted acid sites and strong Lewis acid sites were favorable to the conversion of methanol and formation of long-chain PODEn,respectively.The reaction parameters such as catalyst amount,molar ratio of FA/MeOH,reaction time,temperature and pressure were optimized.The speculated reaction pathway for PODEn synthesis was proposed based on the synergy of Brønsted and Lewis acid sites,which suggested that Brønsted and Lewis acid sites might be advantageous to the activation of polyoxymethylene hemiformals[CH_(3)(OCH_(2))_(n)OH]and methylene glycol(HOCH_(2)OH),respectively.