弹性体的极性对高密度聚乙烯/胶粉/弹性体三元体系相结构的影响(英语)

研究了非极性弹性体乙烯-辛烯共聚物（POE）和极性弹性体乙烯-乙酸乙烯酯（EVA）对高密度聚乙烯/胶粉/弹性体三元体系相结构的影响。结果表明,POE形成包埋结构,而EVA形成分散结构。     

低硬度乙烯-乙酸乙烯酯共聚物/聚烯烃弹性体/充油丁苯橡胶热塑性硫化胶的性能

采用动态硫化法制备了乙烯-乙酸乙烯酯共聚物/充油丁苯橡胶热塑性硫化胶(EVA/SBR TPV),在此基础上以聚烯烃弹性体(POE)替代部分EVA制备出低硬度TPV,并对其力学性能、Mullins效应和微观形貌进行了研究。结果表明,当EVA/SBR(质量比)为30/70时,TPV的综合性能良好;当EVA/POE/SBR(质量比)为25/5/70~20/10/70时,TPV的扯断伸长率超过1 000%,邵尔A硬度在50左右。EVA/POE/SBR TPV存在明显的Mullins效应,拉伸比一定时,最大应力和内耗随循环拉伸次数的增加而下降,瞬时残留变形则逐渐增大;拉伸比增大时,最大应力、瞬时残留变形和内耗均增加。基体中POE的存在赋予TPV更强的弹性回复能力。     

POE和EVA对IXPE发泡材料的改性研究

研究添加不同比例EVA树脂（乙烯-乙酸乙烯酯）和弹性体POE（乙烯-辛烯共聚物）对IXPE发泡材料的表观密度、拉伸性能及泡孔结构的影响。结果表明POE和EVA添加量增加,IXPE表观密度增大;当POE/EVA〈26份时,POE对IXPE发泡材料的拉伸强度的改性效果优于EVA,当POE/EVA〉26份时,EVA对IXPE发泡材料的拉伸强度的改性效果优于POE;POE对IXPE发泡材料断裂伸长率的改性效果较好;添加不同比例POE和EVA,都能制备出泡孔结构均匀IXPE发泡材料。     

动态硫化EPDM/EVA热塑性弹性体的制备与性能

采用动态硫化法制备了三元乙丙橡胶(EPDM)/乙烯-醋酸乙烯共聚物(EVA)共混型热塑性弹性体(TPE),并对其力学性能和微观相结构进行了研究。结果表明,动态硫化EPDM/EVA型TPE的拉伸强度及撕裂强度均随EVA含量的增加而提高,当EVA含量低于50wt.%时,其应力-应变曲线呈现出典型的弹性体特征;EPDM/EVA的共混比为60/40时,所制备的TPE表现出了良好的综合性能;EPDM分散相粒径在20μm以下且较均匀地分散EVA基体中。     

POE/硅橡胶热塑性弹性体的力学性能及加工性能研究

采用动态硫化方法制备了乙烯-丙烯共聚物(POE)/硅橡胶热塑性弹性体。考察了共混比和交联剂含量对POE/硅橡胶热塑性弹性体的力学性能以及流变加工特性的影响。结果表明,m(硅橡胶)/m(POE)为60/40,交联剂质量分数为2.5%时表现出优越的力学性能,拉伸强度达到9.8MPa,断裂伸长率达到740%。制备出的POE/硅橡胶在流变测试中表现出优越的流变性能,具有高剪切粘度低,低剪切粘度高的特点。     

乙烯-乙酸乙烯酯共聚物/聚甲醛动态硫化热塑性弹性体的制备

以1,1-二叔丁基过氧基-3,3,5-三甲基环己烷(Luperox231)/N,N’-间苯撑双马来酰亚胺(HVA-2)为硫化体系,采用反应挤出动态硫化法制备了乙烯-乙酸乙烯酯共聚物(EVA)/聚甲醛(POM)动态硫化热塑性弹性体。结果表明,EVA/POM动态硫化热塑性弹性体的综合力学性能明显改善,拉伸强度可达到12 MPa左右,但断裂伸长率较低;螺杆转速和挤出机加工温度对EVA/POM动态硫化热塑性弹性体的力学性能有影响,为制备性能良好的EVA/POM动态硫化热塑性弹性体,螺杆转速设定为250r/min,挤出机加工温度为145~175℃;Luperox231用量的增加使动态硫化热塑性弹性体的拉伸强度和断裂伸长率、永久变形以及肖D硬度均下降,而HVA-2用量的增加使动态硫化热塑性弹性体的拉伸强度和永久变形呈先降低后升高的趋势。     

聚烯烃弹性体对剑麻纤维增强聚丙烯复合材料性能的影响

为提高剑麻(SF)增强聚丙烯(PP)复合材料的韧性,分别采取乙烯-辛烯共聚物(POE)和马来酸酐接枝POE(POE-g-MAH)二种弹性体对其进行增韧改性;研究了弹性体和纤维用量的变化对SF/PP/弹性体三元复合体系力学性能的影响及其内在原因。结果表明:POE和POE-g-MAH对剑麻增强聚丙烯复合材料均有良好的增韧效果;仅从增韧效果而言,在弹性体用量较低阶段POE优于POE-g-MAH,但当弹性体增至30%以后,POE-g-MAH则好于POE;在拉伸强度、拉伸模量、弯曲强度及弯曲模量方面,POE-g-MAH均比POE效果更好。     

PP/POE热塑性弹性体的动态流变性能研究

研究了聚丙烯/乙烯-辛烯共聚物(PP/POE)动态硫化热塑性弹性体的动态流变性能。结果表明:2,5-二甲基-2,5-双(过氧化叔丁基)己烷(DBPH)交联的材料弹性较好,随着过氧化物用量的增加,PP/POE体系的能量损耗减少,弹性增加。TAIC交联材料的内耗较小,加入TAIC抑制了PP的降解,并使材料的内耗减少,含量越多内耗越少。在不同比例的PP/POE体系中,较低的振动频率下POE控制材料的弹性模量,较高的振动频率下PP控制材料的弹性模量。     

具有网络形态的热塑性聚氨酯／聚烯烃弹性体共混体系的研究

通过熔融共混法制备了热塑性聚氨酯（TPU）分别与三元乙丙橡胶（EPDM）、乙烯-辛烯共聚物（POE）、苯乙烯-丁二烯-苯乙烯三嵌段共聚物（SBS）共混。对三种共混体系的形态结构研究显示，这三种聚烯烃弹性体在TPU基体中均形成了网络结构。网络状结构的形成使TPU的拉伸强度、断裂伸长率和拉伸模量得到显著提高，其熔体中形成的分子链互锁也使共混体系的平衡扭矩增加。由于三种不同聚烯烃弹性体与TPU的极性差不同，导致了网络状形态结构的完整性出现差异，因而使其显示了不同的增强效果，其中EPDM最佳，POE其次，而S13S与TPU的极性差最小，增强效果也最差。     

高密度聚乙烯/聚烯烃弹性体/三元乙丙橡胶热塑性弹性体的结构与性能

采用动态硫化法制备了高密度聚乙烯(HDPE)/三元乙丙橡胶(EPDM)热塑性弹性体(TPV),并在基体中添加聚烯烃弹性体(POE)以改善其性能.对所制得的TPV的力学性能、微观相结构和动态黏弹行为进行了研究.结果表明,当HDPE/EPDM(质量比)为40/60时,HDPE/EPDM TPV表现出良好的综合性能;用POE...     

Polymorphism of LiGa5O8 and of LiGa5O8-MgGa2O4Solid Solutions

High-temperature X-ray diffraction and differential thermal analyses showed that LiGa₅O₈ exists in two polymorphs related by the first-order transition at 1138°±3°C of the low-temperature simple-cubic form, space group (probably) O⁷, to the high-temperature spinel (fcc) form, space group O _h ⁷. The transition is rapid, and the high-temperature form in pure LiGa₅O₈ could not be quenched to room temperature under the conditions used. However, the high-temperature polymorph can be quenched under equilibrium conditions when 40 mol% or more MgGa₂O₄ is present. The subsolidus equilibrium relations in the system MgGa₂O₄-LiGa₅O₈ are discussed.     

Magnetoresistance of CuxCo1-xFe2O4 Ferrites

Magnetoresistance measurements (Δ/R) were carried out on Cu _x Co_{1- x} Fe₂O₄ samples with x =1, 0.75, 0.50, 0.25 and cobalt ferrite in the range of magnetic intensity (H) from 1.0 to 4.5 kG. Linear plots were obtained between log (Δ/R) and log H for all compositions except that of cobalt ferrite. The values of n at x =0.5 do not agree with the results of some authors. The discrepancy may be attributed to the value of magnetic field intensity at which such measurements were carried out. The similarity of features of n and μ_D with composition leads us to believe that the magnetoresistance may arise from the scattering of conduction electrons by localized electrons involving the s-d exchange interaction.     

Sintering of Si3N4-Y2O3-Al2O3

Sintering kinetics of the system Si₃N4-Y2O₃-Al₂O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si₃N₄ were studied with additions of 4 to 17 wt% Y₂O₃ and 4 wt% A1₂O₃. Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ' -Si₃N₄ and glass or β '-Si₃N₄, α '-Si₃N₄, and glass. The compositions and amounts of the residual glassy phases are estimated.     

Expansive properties of the mixture C4ASH12 − 2CS III. Effects of temperature and restraint

The effects of temperature and restraint upon the hydration and the expansion of $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}\text{? 2}\text{C}\text{S}$ mixture compacts in different contact solutions have been investigated. Temperatures above 20°C do apparently hinder the formation of an impervious felt-like layer of ettringite around the $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}$ particles, thus greatly reducing the retarding effect of the lime. An uniaxial restraint of 1 Kg/cm² is enough to reduce sensibly the expansions which remain however high (about 100%). The results can be satisfactorily interpreted by the reaction and expansion mechanism hypothesized in our previous papers.     

Raman Study of Glasses of Ba2TiSi2O8 and Ba2TiGe2O8

Raman spectra are reported for fresnoite (Ba₂Ti(Si,Ge)₂O₈ glasses, and comparison is made between the Raman spectra of the corresponding crystalline powders and glasses of Ba₂TiSi₂O₈ and Ba₂TiGe₂O₈. The Ba₂TiGe₂O₈ glass spectra show correspondence with the Ba₂TiGe₂O₈ crystalline Raman spectra; the v _s(Ge–O–Ge) mode occurs at 518 cm⁻¹ in the glass and at 521 cm⁻¹ in the crystalline material. Five-fold coordinated titanium is the majority species present in the Ba₂TiGe₂O₈ glass as revealed by a strong band at 824 cm⁻¹ in the I glass spectrum. The Ba₂TiSi₂O₈ glass spectra are similar to the Ba₂TiSi₂O₈ crystalline spectrum; the strongest band is found at 836 cm⁻¹ in the I glass spectrum. Through comparison with the previous Raman data of other titania silicate glasses, we conclude that the Ba₂TiSi₂O₈ glass has a structure similar to the crystalline phase.     

Preparation and properties of poly(Nε,Nε-dicarboxymethyl-l-lysine)

A new ampholytic homopolypeptide, $\text{poly}\text{(N}{}^{\mathrm{\epsilon }}\text{,N}{}^{\mathrm{\epsilon }}\text{-}\text{dicarboxy-methyl-}\text{l}\text{-lysine}\text{)}$, which has one tertiary amino and two carboxyl groups in the side chain has been derived from a hydrochloride salt of poly(L-lysine). The polymer in aqueous solution seems to be in the coil form with locally extended structure (LES) at neutral pH. In both the acidic and alkaline regions, the molar ellipticity of the polymer changes as a result of change in net charge on the side chain. The conformational changes may be from the coil with LES to other coiled forms. 5–7 M NaClO₄ and 80% aqueous methanol induce the α-helix in the polymer at neutral pH. Divalent cations, Cu²⁺ and Ca²⁺, do not induce any remarkably ordered structures such as α-helix or β-structure in the polymer in aqueous solution at any pH. Ultraviolet absorption studies show an absorption peak of the polymer-Cu²⁺ complex near 240 nm. Dependence of the peak intensity on pH at various q values ($\text{q =}\text{[}\text{Cu}{}^{\mathrm{2+}}\text{]}\text{[}\text{residue}\text{]}$) indicates the two steps of the complex formation. At q less than 0.64, the formation is described only with the first step. An average coordination number for Cu²⁺ at the first step was calculated to be about 2 by the method of Mandel and Leyte. The association constant of Cu²⁺ with the residue at the step was determined from the absorption data to be far smaller than that for the Cu²⁺-EDTA complex. The second step of the formation occurs in the case of large q but the absorption data for the second step cannot be obtained exactly due to precipitation.     

Effects of metal-support interactions on the hydrogenation of CO over PdSiO2 and PdLa2O3

A study of CO hydrogenation over $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$ has been carried out for the purpose of identifying the effects of Pd dispersion, Pd morphology, and support composition on the catalytic activity of supported Pd. The specific activity of each catalyst for methanol and methane synthesis was determined from microreactor studies carried out at a fixed set of reaction conditions. Palladium dispersion was measured by H₂O₂ titration, and the morphology of the Pd crystallites, as expressed by the distribution of Pd(100) and Pd(111) planes, was determined from in situ infrared spectra of adsorbed CO. The crystallite morphology of the $\text{Pd}\text{SiO}{}_2$ catalysts is the same, independent of Pd weight loading: 90% of the surface is comprised of Pd(100) planes and 10% of the surface is comprised of Pd(111) planes. By contrast, the crystallite morphology of the $\text{Pd}\text{La}{}_2\text{O}{}_3$ catalysts changes with Pd loading. Primarily Pd(100) planes are exposed at low-weight loadings while Pd(111) planes are exposed at high-weight loadings. The Pd dispersion has little effect on the methanol turnover frequency over both $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$, for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over $\text{Pd}\text{SiO}{}_2$, but increases with decreasing dispersion over $\text{Pd}\text{La}{}_2\text{O}{}_3$. It is further observed that the Pd morphology influences the specific activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ is a factor of 7.5 greater than that of $\text{Pd}\text{SiO}{}_2$.     

In situ laser raman spectroscopy of the sulfiding of Moγ-Al2O3 catalysts

Raman spectra of sulfided $\text{Mo}\text{γ-}\text{Al}{}_2\text{O}{}_3$ catalysts were obtained using in situ techniques for two sulfiding methods. For samples sulfided by 10% $\text{H}{}_2\text{S}\text{H}{}_2$ at 400 °C, MoS₂ structures were observed. A stepwise sulfiding using 10% $\text{H}{}_2\text{S}\text{H}{}_2$, with spectra recorded at 150, 250, and 350 °C, resulted in observation of molybdenum oxysulfide, reduced molybdate, and surface “MoS₂” phases. Reexposure of these samples to air led to radical modification of the oxysulfide structures as well as transformation of some sulfide phases. A model incorporating terminal and bridging MoS bonding and anion vacancies is proposed. This model is based on the conversion of isolated and aggregated molybdate and MoO₃ species to oxysulfide and reduced molybdenum phases. Conversion of reduced molybdenum phases to sulfides is observed to be slow.     

Wet Milling of Fe/Al/Al2O3 and Fe2O3/Al/Al2O3 Powder Mixtures

Wet milling of Al₂O₃-aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al₂O₃ and Fe₂O₃/Al/Al₂O₃ powder mixtures. The influence of the milling process on the physical and chemical properties of the milled powders has been studied. Particle refinement and homogenization were found not to play a dominant role, whereas plastic deformation of the metal particles leads to the formation of dislocations and a highly disarranged polycrystalline structure. Although no chemical reactions among the powder components in Fe₂O₃/Al/Al₂O₃ powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al₂O₃ powder mixtures caused by mechanical alloying was detected. Chemical reactions of Fe and Al particle surfaces with the atmosphere and the milling media lead to the formation of highly porous hydroxides on the particle surfaces. Hence the specific surface area of the powders increases, while the powder density decreases during milling. The fraction of Fe oxidized during milling was determined to be 0.13. The fraction of Al oxidized during milling strongly depends on the metal content of the powder mixture. It ranges between 0.4 and 0.8.