氯丁橡胶/有机粘土纳米复合材料的拉伸诱导结晶行为研究

通过熔体插层法制备氯丁橡胶(CR)/有机粘土纳米复合材料(CRCNs),研究有机粘土用量对CRCNs拉伸诱导结晶行为的影响。结果表明:随着应变增大,CRCNs的应力增大,当应变达到一定值时,应力迅速增大,诱导结晶集中产生;随着有机粘土用量增大,CRCNs发生拉伸诱导结晶行为的应变增大;当有机粘土用量为5份时,CRCNs的拉伸性能较好,CRCNs中橡胶分子链成功插层进入有机粘土片层,有效扩大了有机粘土层间距,有机粘土与橡胶基体界面作用较强,在橡胶基体中的分散较均匀。     

黏土含量与结构对天然橡胶拉伸诱导结晶行为的影响

采用熔体法制备天然橡胶/有机黏土纳米复合材料(NRCNs),重点考察黏土片层结构及其含量对拉伸结晶型橡胶拉伸诱导结晶行为的影响。并通过XRD、TEM等测试表征NRCNs的微观相态结构。实验结果表明:随着拉伸形变的增加,NRCNs的定伸应力逐渐增加;当达到某一临界应变值ε_0时,NRCNs的定伸应力快速增加——拉伸诱导结晶行为产生;随着有机黏土含量的增加,NRCNs拉伸诱导结晶行为在较低的应变下产生,这主要是因为纳米分散的有机黏土具有较大的形状系数,对橡胶分子链具有较强的限制作用,刚性平行黏土片层结构有利于促进柔性橡胶分子链在拉伸形变过程中快速取向。     

顺丁橡胶/有机黏土纳米复合材料的拉伸诱导结晶行为

采用熔体法制备了顺丁橡胶/有机黏土(OC)纳米复合材料(BRCNs),通过偏光显微镜观察BRCNs在不同拉伸情况下的聚集态结构,并研究了OC的结构及用量对顺丁橡胶拉伸诱导结晶行为的影响。结果表明,随着拉伸形变的增加,BRCNs的定伸应力呈增大趋势;当应变达到某一值时,BRCNs的定伸应力迅速增加,拉伸结晶化集中产生;随着OC用量的增加,BRCNs拉伸诱导结晶行为在较低的应变条件下产生。     

异戊橡胶/有机黏土纳米复合材料的力学性能及相态结构

研究了异戊橡胶/有机黏土纳米复合材料(IRCNs)的硫化特性及力学性能,通过X射线衍射仪和扫描电镜表征了IRCNs的相态结构。结果表明,随着有机黏土用量的增加,IRCNs的拉伸强度表现出先升高后降低的变化规律,当有机黏土用量为5份时,IRCNs的拉伸强度达到最大。拉伸循环后IRCNs的临界应变值增加,表明其拉伸诱导结晶行为更容易在高应变下发生。在IRCNs内有机黏土片层均匀地分散于异戊橡胶基体中,并且异戊橡胶大分子插层进入了有机黏土片层之间,使得有机黏土的层间距增大,形成了插层结构,起到了补强作用。     

天然胶乳/有机粘土复合材料的结构和拉伸诱导结晶行为研究

采用乳液法制备天然胶乳/有机粘土纳米复合材料(NRLCNs),研究NRLCNs的结构、试样厚度和有机粘土用量对NRLCNs拉伸诱导结晶行为的影响。结果表明:NRLCNs为插层型结构,NRLCNs的物理性能明显优于NRL胶料;试样厚度相同时,有机粘土用量为3份的NRLCNs物理性能最优;有机粘土用量相同时,试样厚度较小的NRLCNs物理性能较优;随着拉伸强度的增大,NRLCNs的定伸应力逐渐增大,当达到临界应变值时,定伸应力迅速增大,产生拉伸诱导结晶行为,试样厚度较小的NRLCNs易产生拉伸诱导结晶行为。     

有机粘土/异戊橡胶纳米复合材料应变诱导结晶行为的研究

制备有机粘土(OC)/异戊橡胶(IR)纳米复合材料(IRCNs),研究OC用量对IRCNs拉伸性能和应变诱导结晶行为的影响。结果表明:IRCNs中OC的衍射峰角度较OC不同程度减小,且细致、均匀地分散于橡胶基体中,形成有序插层结构;随着OC用量增大,IRCNs的拉伸强度先增大后减小,当OC用量为5份时,IRCNs的拉伸强度最大(16. 44 MPa),较IR提高41%;IRCNs的应变诱导结晶行为随着OC用量增大向低应变转移,应力临界诱变点逐渐减小;当应变小于应力临界诱变点时,IRCNs中OC的取向度较低,当应变大于应力临界诱变点时,OC取向明显并趋于极限。     

高密度聚乙烯/黏土纳米复合材料的研究进展

主要论述了高密度聚乙烯(PE-HD)/黏土纳米复合材料的制备因素对结构形态的影响及其性能的研究进展。当前的研究表明,黏土有机化处理和使用相容剂能改善材料的插层和剥离结构;PE-HD基体对结构的影响比较复杂,一方面,随着聚合物相对分子质量的增加,聚合物分子链的尺寸增加,分子链长的聚合物更难进入到黏土夹层间,不利于黏土的剥离;另一方面,黏度随相对分子质量的增加而增加,黏度的增加在熔融加工过程中可提高熔体的剪切力,有利于聚合物进入堆叠的纳米黏土层间,使得片层分离而达到剥离结构;黏土加入量过高不利于得到剥离结构;在加工工艺上,母料法比直接混合法得到的插层效果好,选择合适的设备、对螺杆进行优化设计以提高剪切效果,有利于得到插层和剥离结构的PE-HD/黏土纳米复合材料。PE-HD/黏土纳米复合材料的性能研究表明,由于黏土没达到完全剥离和均匀分散,纳米复合材料的脆性增加,韧性降低,且随黏土含量的增加脆性增加,这与PE-HD和黏土界面相间的相互作用密切相关;黏土粒子分散程度越高,其与熔体接触面积越大,PE-HD分子链运动受阻,材料弹性提高;纳米复合材料中黏土层作为二维异向成核剂,可以提高材料的结晶速率,使结晶温度升高,黏土含量过大会降低结晶度;黏土分散不均会造成复合材料的气体渗透性降低;一方面,片层的阻透效应可提高材料热稳定性,另一方面,有机改性黏土的催化作用又会使PE降解而降低其热稳定性,当黏土含量适中时,黏土片层均匀分散,阻透性能起主要作用,但随着黏土含量的增加,催化作用迅速加强并成为主要因素,使复合材料热稳定性降低;此外,燃烧过程中形成焦烧物可提高PE-HD/黏土纳米复合材料的阻燃性。     

有机粘土/天然胶乳纳米复合材料的循环拉伸诱导结晶行为研究

采用乳液插层法制备有机粘土（OC）/天然胶乳（NRL）纳米复合材料（NRLCNs）,研究OC用量和循环拉伸对NRLCNs拉伸诱导结晶行为的影响。结果表明：NRLCNs为插层结构,随着OC用量的增大,NRLCNs的拉伸强度先增大后减小,当OC用量为4份时,NRLCNs的力学性能达到最佳,拉伸强度为15.86 MPa,较天然橡胶胶料（未加OC）的拉伸强度提高58%;OC的加入有助于NRLCNs发生拉伸诱导结晶,随着其用量的增大,NRLCNs的拉伸结晶临界诱变点的拉伸应变减小;经过循环拉伸处理的NRLCNs橡胶分子产生了一定的取向,再次拉伸时能够更快地达到拉伸结晶临界诱变点,产生拉伸诱导结晶。     

撕裂模式下EAA/CR TPV的Mullins效应及其可逆回复行为

采用动态硫化法制备了乙烯-丙烯酸共聚物(EAA)/氯丁橡胶(CR)热塑性硫化胶(TPV),研究了其微观相结构、撕裂模式下的Mullins效应及热处理条件下的Mullins效应的可逆回复行为。结果表明,TPV的微观形貌呈明显的"海岛"结构;在EAA/CR TPV的单轴循环撕裂过程中出现了明显的Mullins效应,且随着应变的增大,最大撕裂强度、瞬时残余应变、内耗和tanδ呈明显上升趋势,但应力软化因子则持续下降;当应变一定时,随着循环次数的增加,瞬时残余应变和应力软化因子随之增大,最大撕裂强度、内耗和tanδ则逐渐减小;对单轴循环撕裂测试后的样品进行热处理,其Mullins效应的回复程度获得提高,且在100℃的热处理温度下回复效果最佳。     

PE/OC纳米复合材料的结晶性能与流变性能

以聚乙烯(PE)为基体,通过熔融插层法将有机黏土(OC)加入到PE基体中,制备了PE/OC纳米复合材料,并对复合材料的微观结构、结晶性能、流变性能以及力学性能进行表征测试.结果表明:w(OC)为3％时,PE/OC纳米复合材料形成了部分剥离型结构,复合材料的结晶度最大,且拉伸强度最大,达27.6?MPa,但随着OC含量进...     

New insights into thermodynamic description of strain-induced crystallization of peroxide cross-linked natural rubber filled with clay by tube model

Clay changes the strain-induced crystallization behavior of natural rubber and induces a dual crystallization mechanism due to the orientation of clay layers during deformation. The structure evolution was probed by in-situ synchrotron wide-angle X-ray diffraction, while the thermodynamics of the onset of crystallization was analyzed by the tube model. The entropy change required for the onset of the strain-induced crystallization of the clay filled rubber is composed of the entropy reduction due to the rubber-filler interactions and also the stretching. The summation of the two kinds of the entropy reduction is nearly equal to that of the neat rubber. The thermodynamic analysis reveals that the orientation of clay layers along the direction of stretching reduces the chain conformational entropy and changes the crystallization mechanism. These results give some new insights into the strain-induced crystallization process and the reinforcement mechanism for the clay filled rubber.     

The isothermal crystallization of crosslinked polyethylene under uniaxial extension

An experimental study of the crystallization of chemically crosslinked polyethylene at constant strain under isothermal conditions was carried out. Changes in the stress and birefringence were measured simultaneously as a function of time. Both the stress and the birefringence behavior are consistent with previous work carried out under constant rate of cooling conditions. This indicates that the cooling conditions do not affect the structural features of the crystallization process. A comparison of the stress and birefringence curves shows that there are periods off time during which both stress and birefringence increase; stress increases and birefringence decreases; stress decreases and birefringence increases; and both stress and birefringence decrease. None of the crystal morphological models proposed to date for the strain-induced crystallization of crosslinked polyethylene appear to be able to account fully for this behavior.     

Effect of diethylene glycol (DEG) on the crystallization behavior of poly(ethylene terephthalate) (PET)

The effect of diethylene glycol (DEG) on the crystallization of poly(ethylene terephthalate) (PET) was studied under isothermal and dynamic conditions. The strain-induced crystallization of PET and its relationship to DEG content was also studied. The samples were isothermally and dynamically crystallized in the differential scanning calorimeter (DSC). The thermograms were then analyzed to determine the kinetic parameters. Strain-induced crystallization was studied by stretching samples at different strain rates. These samples were then annealed for various periods of time and quenched to room temperature. Birefringence and density were measured on the annealed samples. Results indicate that the DEG content reduces the rate of crystallization of PET when crystallizing from the melt, isothermally and dynamically. When crystallizing from the glassy state, the effects of DEG are not prominent. The mechanism of crystallization is not affected by the amount of DEG, within the range of DEG contents evaluated. In the case of strain-induced crystallization, increased DEG content reduces the crystallinity of PET at intermediate strain rates, but at higher strain rates, the crystallinity is not affected by the DEG content. © 1993 John Wiley & Sons, Inc.     

“Mechanism of the self-reinforcement of cross-linked NR generated through the strain-induced crystallization”

The author proposed new models and concept for the self-reinforcement of NR. The first model indicates that general rubber vulcanizate consists of the heterogeneous structure, partially continuous cross-linked phase (75%) and continuous uncross-linked phase (25%). In addition, the author proposed other new models and concept for the strain-induced crystallization in vulcanized NR, in which the strain-induced crystallization takes place in the uncross-linked phase in cross-linked rubber. In the uncross-linked phase under large extension, molecular flow and orientation occur due to the very high compressive, shear and tensile stresses generated by the surrounding hard cross-linked phases, which makes the strain-induced crystallization possible in the uncross-linked phase. As macroscopic extension increases, the crystallization spreads over the whole uncross-linked phases, thus the uncross-linked phase changes its character from original soft rubber to the strong super network consisting of a bundle of extended molecules interconnected at the crystals. The characteristic phenomena observed in the stress-strain relation of NR such as the stress-upturn, high tensile strength and large stress-softening (Mullins effect) can be reasonably explained using these models and concepts.     

A stroboscopic X-ray apparatus for the study of the kinetics of strain-induced crystallization in natural rubber

A stroboscopic X-ray diffraction machine is described that allows studying kinetics aspects of strain-induced crystallization in natural rubber. Besides conventional mechanical cycling in extension, samples may be submitted to periodic extension cycling over a 0.05 Hz–30 Hz frequency range and for various amplitudes of elongation. Pertinent parameters as crystalline content, crystallite orientation and segmental order parameter for the amorphous fraction are determined. The existence of a regulation process of the strain experienced by the chains that remain molten due to the phenomenon of strain-induced crystallization is clearly demonstrated during conventional mechanical cycling at low deformation rate. Melting retardation is shown to lead to an equalization of crystalline content in conditions of periodic cycling of moderate amplitude and below some average elongation. On the other hand, crystallization appears to be a rapid process subsisting up to the maximal cycling frequency corresponding to a stretching time of 17 ms. This is confirmed by periodic cycling of higher amplitude that suggests that strain-induced crystallization may appear within millisecond time. An approximate logarithmic dependence of the crystalline content and elongation of the amorphous fraction upon stretching time is further found.     

Strain-induced crystallization of cis-1,4-polybutadiene containing dispersed 1,2-polybutadiene crystalline particles

Some grades of cis-1,4-polybutadiene contain dispersed crystalline particles made up of a block copolymer having amorphous cis-1,4- and crystalline 1,2 blocks. The particles are known to enhance the strain-induced crystallization of cis-1,4 matrix rubber. The deformational behavior was examined by dynamic shear measurements at small deformation and tensile stress–strain measurements at large deformation. In the shear measurements (linear behavior), the temperature dependence of the shift factor in the time-temperature superposition has been evaluated. The higher temperature dependence was observed for the lower crystalline particle content and higher degree of branching of the matrix rubber. The presence of the crystalline particles resulted in the viscosity enhancement like that expected from the dispersed particles. In the tensile measurements (non-linear behavior), the rubbers showed strain softening. The higher degree of strain softening was observed for the higher amount of the crystalline particles and lower degree of branching. The strain softening is a result of the crystalline particles facilitating the elongation. Because these particles posses the branches which are cis-1,4 chains of the block copolymer, the branches are lubricating the system during the stretching. The length of the branches must be short enough so as to produce no significant entanglement constraint. This observation is in accord with the previous one that a relatively long branch gives strain hardening, whereas a relatively short branch gives strain softening. The strain softening was found to enhance the strain-induced crystallization. This conclusion is opposite to what one might expect from the entanglement constraints by the long branches, forcing the orientation of the chains, and thus enhancing the strain-induced crystallization. © 1996 John Wiley & Sons, Inc.     

Intercalation process and rubber–filler interactions of polybutadiene rubber/organoclay nanocomposites

The intercalation process and microstructural development of polybutadiene rubber (BR)/clay nanocomposites cured with sulfur were systematically investigated with respect to the organic modifier (primary and quaternary ammonium compounds) of the clay. X‐ray diffraction spectra were recorded at various stages of processing to obtain information about the intercalation process. The rubber–filler interactions was examined on the basis of the surface free energy, stress‐softening effect, and crystallization behavior. A well‐ordered intercalated structure was obtained in the primary ammonium modified clay (P‐OMMT) and quaternary ammonium modified clay (Q‐OMMT) filled with BR composite. The BR/Q‐OMMT composites showed higher mechanical properties and higher hysteresis under tension and lower crystallization abilities than the BR/P‐OMMT composites. The results also show that higher interfacial interactions existed between Q‐OMMT and BR than between P‐OMMT and BR. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of EPDM on LDPE/LLDPE blends: mechanical properties

Blends of two polyethylenes and an elastomer were prepared to investigate the effect of the latter polymer. The blends contain equal parts of low density (LDPE) and linear low density polyethylene (LLDPE), and ethylene–propylene–diene rubber (EPDM) with variable content ranging from 0 to 17.5%. Melt-mixed blends were prepared using a single-screw extruder. The influence on the mechanical properties of the following factors were analyzed: EPDM content, stretching rate in the range from 10 to 750 mm/min, and two cooling conditions. From the equilibrium torque the miscibility was analyzed. The structure exhibited by the stress–strain (–) curve of the polyethylenes blend is reduced with the addition of the elastomeric phase, and the ultimate properties increase because the amorphous phase becomes softer and reduces its capability to transmit the applied stress to the crystalline particles. The slope of the – curve in the strain hardening region shows a maximum value at the stretching rate ∼ 50–80 mm/min, which is explained partially in terms of the strain-induced crystallization of the polyethylene components. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 677-683, 1997     

Peel Adhesion of Natural Rubber Bonded to Polyethylene Terephthalate: Effect of Crosslinking on Rate/Temperature Response

Laminates consisting of natural rubber (NR) sandwiched between cloth fabric and polyester film were pulled apart at various rates and temperatures in a T-peel geometry. Peel energies for joints containing uncrosslinked or lightly-crosslinked NR did not obey simple time-temperature superposition. This behavior is attributed to strain-induced crystallization during peeling. However, when the rubber was highly crosslinked, strain crystallization seems to be absent, as peel energies now can be WLF shifted to form a mastercurve.     

Peel Adhesion of Natural Rubber Bonded to Polyethylene Terephthalate: Effect of Crosslinking on Rate/Temperature Response

Laminates consisting of natural rubber (NR) sandwiched between cloth fabric and polyester film were pulled apart at various rates and temperatures in a T-peel geometry. Peel energies for joints containing uncrosslinked or lightly-crosslinked NR did not obey simple time-temperature superposition. This behavior is attributed to strain-induced crystallization during peeling. However, when the rubber was highly crosslinked, strain crystallization seems to be absent, as peel energies now can be WLF shifted to form a mastercurve.