Effect of types of carbon black and cure conditions on dynamic mechanical properties of elastomers

The dynamic mechanical properties of natural rubber and bromobutyl rubber (used in automotive suspension parts) were investigated to determine the effect of particle size of carbon black filler and state of cure of the rubber matrix. The results indicate that state of cure has little effect on storage modulus (hardness and stiffness). However, elastomers with a desirable storage modulus, with low sensitivity to temperature change, can be developed using a filler with a small particle size.     

Effect of cure temperature on urethane networks

Stress relaxation was used over a wide temperature range (?70° to 160°C) to characterize two similarily prepared but differently cured polyurethane networks. Polymer A was cured at 140°C and polymer B was cured at 80°C. The differences in physical properties and responses of the two polymers to the applied strain were consistent with the hypothesis that high cure temperatures produce a more chemically (biuret) crosslinked structure whereas low cure temperatures favour a domain-separated structure. Polymer A (high cure temperature) strain-crystallized below 0°C, had a longer rubber-modulus than that of polymer B, and showed a load—deflection curve more typical of a chemically crosslinked polymer.     

Structural determination of Torlon 4000T polyamide-imide by NMR spectroscopy

High field ¹H and ¹³C NMR spectroscopy and published information in the scientific literature were combined in the determination of the chemical structure of the commercially available Torlon^® 4000T, a polyamide-imide which is widely used in applications where good mechanical, thermal and oxidative properties are required. It was found from qualitative and quantitative NMR analysis that the three monomers used to synthesize Torlon are as follows: 1.0 trimellitic anhydride chloride, 0.7 4,4′-oxydianiline, 0.3 m-phenylenediamine. It was also shown that the sequence of appearance of the polymer's amide and imide functional groups follows a certain distribution of Amide-Imide, Amide-Amide and Imide-Imide repeat units due to the dual reactive sites, acid chloride and anhydride, of the monomer trimellitic anhydride chloride.     

麦秸刨花板用PMDI胶粘剂固化条件的研究

以麦秸为原料、PMDI为胶粘剂,利用K型热电偶、自动平衡记录仪跟踪检测板材热 压过程中板材中心温度随热压时间的变化情况,初步对PMDI胶粘剂的固化适宜条件加以研 究,以指导生产实践,提高生产效率。     

Influence of cure conditions on properties of resol/layered silicate nanocomposites

The effects on clay exfoliation of organic modification of montmorillonite (MMT) and the nature of the catalyst used during the synthesis and curing of a MMT modified phenolic resol resin were investigated. The impact on the final properties of other parameters such as reactivity ratio and temperature of condensation were also analyzed in order to optimize the conditions to prepare a customized organoclay‐based nanocomposite. Nanocomposites were analyzed by means of wide angle X‐ray scattering (WAXS), optical microscopy (TOM), and atomic force microscopy (AFM) techniques. The formation of either intercalated or quasi‐exfoliated structure was assessed in some systems. Thermal and mechanical properties of the cured composites were evaluated and correlated to their morphologies. More homogenous clay dispersion was achieved for composites prepared with aminoacid‐modified MMT, triethylamine (TEA) as catalyst, formaldehyde/phenol molar ratio (F/P) 2.0, and curing at 80°C. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Miscibility in molecular composites of polyamide-imide/polyetherimide

Summary Compositional dependence of miscibility in molecular composites of polyamide-imide/polyetherimide prepared by coagulation of the blend of the two polymers from dimethyl acetamide solutions has been established by calorimetric and dynamic mechanical thermal studies. This study reports on the thermodynamics of miscibility in the molecular composites.     

Polyetherimide-modified epoxy networks: Influence of cure conditions on morphology and mechanical properties

The morphologies and mechanical properties of thermoplastic-modified epoxy networks generated through the reaction-induced phase separation procedure were studied as a function of isothermal cure conditions. The selected model system was diglycidyl ether of bisphenol A cured with 4,4′-methylenebis [3-chloro,2,6-diethylaniline] in the presence of a nonfunctionalized polyetherimide. Appropriate precuring and postcuring schedules were selected. The precure temperature had a strong effect on final morphologies because it affected the viscosity of the system at the cloud point and the extent of the separation process. The morphologies generated are discussed in connection with phase separation mechanisms. The ratio of the height of the loss peaks corresponding to each phase was an appropriate parameter to qualitatively predict the shape of morphology and to determine if the system was phase-inverted or not. The fracture toughness, K_Ic was significantly improved only when bicontinuous or inverted structures were generated, resulting from the plastic drawing of the thermoplastic-rich phase. Before phase inversion, K_Ic was hardly higher than that of the neat matrix due to poor interfacial adhesion. Nevertheless, the thermoplastic-rich particles constitute obstacles to the propagation of the crack and contribute to the toughening of the material, measured through impact resistance measurements. The observation of fracture surfaces revealed the occurrence of microcracking and crack-pinning. Strain recovery experiments showed that particle-induced shear yielding of the matrix was present as well. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2433–2445, 1997     

Influence of cure conditions on glass transition temperature and density of an epoxy resin

The glass transition temperature T_g and density of a TGDDM-DDS epoxy resin system were studied as a function of cure times at various cure temperatures. Both T_g and density asymptotically increased toward a maximum value with increasing cure time. The T_g and density measurements were related to the extent of cure, and the relationship in both cases was found to be independent of cure temperature.     

Effect of cure temperature on the formation of metakaolinite-based geopolymer

A series of metakaolinite-based geopolymer was prepared at several curing temperatures and its relationship with porosity, infrared spectrometry (FT-IR) and mechanical properties was investigated. The samples were cured at the following temperatures: 55, 65 and 80 °C for 1 h. After a post cure of 28 days, the samples were investigated by using the following techniques: compressive strength, mercury intrusion porosimetry (MIP), helium pycnometry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectrometry (FT-IR). All samples were amorphous by XRD. The sample thermally treated at 65 °C (C65) presented the highest values of compressive strength and relative integrated area of peak at 792 cm⁻¹. This peak was attributed to a higher concentration of tetra-coordinated aluminum, indicating a higher efficiency of the geopolymeric reaction. The C65 also presented the lowest volume of closed pores. The values of the skeletal and the true densities for C65 were very similar and consistent with the volume of the closed pores. On the other hand, this sample showed the highest bulk density obtained by MIP and the greatest difference between the open and closed porosity measured by MIP and helium pycnometry, respectively. All these results are coherent and clearly indicate that the amount of open pores is directly related to a better mechanical performance of the geopolymeric sample.     

Effect of melamine-formaldehyde structure on cure response of thermoset coatings

Reactivity of etherified melamine-formaldehyde (MF) resins with polyol binders depends on the pattern of substitution on off-ring nitrogen atoms. These sites can be doubly substituted [-N(CH₂OCH₃)₂] or singly substituted [-N(H)(CH₂OCH₃)]. The (N-H) portion of singly substituted sites is referred to as an imino group. The main finding of this work is that acid catalyzed cure response is improved greatly when the imino content is reduced to very low levels. The effect of degree of substitution on MF basicity and the site of protonation, ring, or side chain are key elements in the explanation of this cure response behavior. Properties were determined for films cured for 30 min at various temperatures with constant catalyst level and type (0.5 phr paratoluenesulfonic acid). Resins of varying imino content were used. With the MF resin of lowest imino content, extensive cure of acrylic and polyester polyols was observed at cure temperatures as low as 180°F (82°C). Paint tests of hardness and solvent resistance were useful for determining cure response. Dynamic mechanical analysis (DMA) on free films also indicated cure response differences. Storage modulus values from DMA were used to calculate crosslink densities of the thermoset films. Presented at Coatings for Asia ’99, August 30–September 1, 1999, Singapore. 730 Worcester St., Springfield, MA 01151.     

聚酰胺酰亚胺对BMI/DP共聚树脂的增韧研究

以DP(二烯丙基双酚A)为BMI(双马来酰亚胺)的共聚改性剂,制备BMI/DP共聚树脂;然后以PAI(聚酰胺酰亚胺)为增韧改性剂,制备PAI增韧改性BMI/DP共聚树脂。研究结果表明:当w(PAI)=3%(相对于共聚树脂质量而言)时,改性树脂具有较好的增韧效果;此时,其冲击强度(11.81 kJ/m2)提高了19%以上,KIC(临界应力强度因子)值(1.45 MPa.m0.5)和GIC(临界应变能释放率)值(351.4 J/m2)均比增韧前提高了30%以上,表现出较好的断裂韧性,并且其断面为典型的韧性破坏;其Tg(玻璃化转变温度)达到了252.5℃,5%热失重温度仍超过405℃,说明其耐热性几乎没有下降。     

Toughening of a dicyandiamide-cured epoxy resin: Influence of cure conditions on different rubber modifications

Cure kinetics of modified epoxy resins cured with dicyandiamide are studied. The influence of different heating rates in the curing process, such as curing behavior, morphology, and thermo-mechanical properties, is studied. Additionally, three different post-cure cycles at 180°C are employed. Two butadiene-based toughening agents are used, a carboxyl-terminated polybutadiene-co-acrylonitril (CTBN) prepolymer and a functionalized block copolymer of polytetrahydrofuran and hydroxyl-terminated polybutadiene. The amphiphilic block copolymer enables investigations with a bimodal particle size morphology. All results are contrasted with those of the neat resin and butadiene-free block polymer. Faster curing processes result in smaller average particle sizes and better fracture toughness of the modified epoxy resins. Further improvements are achieved with additional post-cure cycles at 180°C. An increased interfacial adhesion between the particles and the epoxy matrix is considered to be the main mechanism. Optimized lengths of the post-cure process can be determined with the butadiene-based toughening agents indicating a competing thermal degradation. Longer post-cures than 40 min lead to lower fracture toughness in the butadiene-based modified materials. In general, similar influences of the curing and post-curing process on the bimodal and unimodal distributed system can be observed differing in more intense dependencies of the bimodal system.     

Effect of initial cure time on toughness of geopolymer matrix composites

The toughness of geopolymer matrix composites (GMC) has been identified as a limiting factor to their use in structural applications. Advanced ceramic matrix composites (CMC), which also are limited by brittle behavior, have shown gains in toughness through careful tailoring of the interface between fiber and matrix. This can create various crack dissipating mechanisms and prevent premature composite failure. Such interface modification has already been applied to a fiber reinforced geopolymer and while the resulting composite showed a reduction in brittle behavior, the modified interface produced an unacceptable loss in modulus without any other well-defined quantitative gains. Information gathered from other studies suggests the large decrease in modulus observed in the GMCs with the weakened interface may have been the result of poor matrix properties stemming from an inadequate cure. Therefore, this current study explores the effects of initial cure time on composite performance by measuring the mechanical properties GMCs with a modified interface. GMCs containing unidirectional Nextel 610 fiber were cured under two different sets of process conditions to better understand the influence of matrix properties. Additionally, specimens consisted of cleaned and carbon coated fiber surfaces, in an attempt to evaluate extremes of interfacial strength. Mechanical properties were then evaluated for comparison to determine if improved geopolymer matrix properties would allow a weakened interface to yield performance gains more in keeping with expectations based on CMC's. The results of the study indicate that specimens with carbon coating benefited from the longer initial cure time. The average increase in flexural modulus and strength over samples with one hour initial cure time was ~65% and ~170% respectively. Stress-strain behavior of the carbon-coated specimens with an extended cure time also indicated a greater degree of damage tolerance as compared to those without interphase.     

Effect of cure kinetic simulation model on optimized thermal cure cycle for thin‐sectioned composite parts

In this article, the optimal design of the thermal cure cycle of a prepreg material has been presented. Three different kinetic methods have been considered to determine the kinetic parameters of the curing reaction of an epoxy/glass prepreg. The capability of these kinetic models in simultaneously predicting kinetic parameters in isothermal and non‐isothermal conditions differs with each other. For the simulation of the cure cycle, a zero‐dimensional model has been used and coupled with the genetic algorithm to optimize the cure cycle of thin composite parts. The effect of the kinetic models on the optimized cure cycle has been investigated. Of these models, only one model could predict the kinetic parameters outside the experimental temperature regions and resulted in a reliable and acceptable optimized cure cycle. The validity of the optimized cure cycle has been also verified experimentally. POLYM. COMPOS., 34:1172–1179, 2013. © 2013 Society of Plastics Engineers     

Miscibility study of Torlon polyamide-imide with Matrimid 5218 polyimide and polybenzimidazole

We have discovered two new miscible polymer blend systems, namely, Torlon^® 4000T with Matrimid^® 5218 and Torlon 4000T with polybenzimidazole (PBI). Both Matrimid 5218 and PBI are miscible at a molecular level with Torlon 4000T over the whole composition range as confirmed by microscopy, DSC, FTIR and DMA. DSC and DMA studies show the existence of a single glass transition in each blend. The T_g-composition curve of Torlon/Matrimid blend system forms a sigmoid curve as a function of composition, while the T_g-composition curve of the Torlon/PBI blend system is double parabola-like. FTIR spectra show the existence of hydrogen-bonding interactions in these two polymer blend systems.     

Influence of cure conditions on out‐of‐autoclave bismaleimide composite laminates

Bismaleimides (BMI) are thermosetting polymers that are widely used in the aerospace industry due to their good physical properties at elevated temperatures and humid environments. BMI‐based composites are used as a replacement for conventional epoxy resins at higher service temperatures. Out‐of‐Autoclave (OOA) processing of BMI composites is similar to that of epoxies but requires higher cure temperatures. Polymer properties such as degree of cure and crosslink density are dependent on the cure cycle used. These properties affect mechanical strength as well as glass transition temperature of the composite. In the current research, carbon fiber/BMI composite laminates were manufactured by OOA processing. The void content was measured using acid digestion techniques. The influence of cure cycle variations on glass transition temperature and mechanical strength was investigated. Properties of manufactured specimens were compared with that of conventional autoclave cured BMI composites. Laminates fabricated via OOA processing exhibited properties comparable to that of autoclave cured composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43984.     

Polyimides: Effect of molecular structure and cure on thermomechanical behavior

The thermomechanical spectra (～0.5 → 1 cps) of systematically related polyimides synthesized from four aromatic dianhydrides and eleven aromatic diamines are discussed with respect to structure-property relationships and cure. In displaying two main transitions, T_g and T_β, most of the polymers behave as amorphous materials such as polymethylmethacrylate. A different mechanism for the relaxations is invoked which involves more intermolecular interaction for those polymers (from pyromellitic dianhydride) which give more complex behavior. Difficulties in obtaining structure-property relationships in the field of high temperature rigid polymers are discussed in terms of defects in molecular structure, the effect of vitrification in freezing out reactions during cure, different chemical reactivities of the reactive precursor polyamic acids, and the effects of thermal reactions which occur in the vicinity of the glass transition regions.     

关于300D/32F扁平丝FDY工艺条件探讨

现在市场上的同质化产品太多,多样化面料价格居高不下,为满足客户需求和改善行业竞争模式,对涤纶扁平300 D/32 F工艺讨论.在生产中不断调整工艺参数,检测产品品质.通过优化工艺可以稳定生产出AA率高的异形扁平FDY 300D/32F全消光丝.     

Effect of cure systems on shrinkability of polyolefin–EPDM blends

Effects of cure systems on shrinkability of polyolefin and EPDM blends have been studied as a function of cure time and amount of elastomers added. During measurement one of the parameters is kept constant while the other varies. The shrinkability of the blends increases with the increase in cure time when elastomer content is fixed. Similarly, at constant cure time higher loading of elastomer increases the shrinkability of the blends. Samples stretched under high temperature show higher shrinkability than those stretched under room temperature. Dicumylperoxide (DCP) is a more effective curing agent for making a particular set of blends more shrinkable than the sulfur. The changing morphological pattern with DCP-cured shrunk samples from those of sulfur cured samples is corroborated by the SEM studies where the elastomer phase appears to be globular in nature. The crystallinity of the blend depends on the dose and type of the elastomer used in polyolefin. The curing efficiency of the elastomerphase depends on the polyolefin used as blend partner. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 597–603, 1998