体积收缩率对光固化树脂基复合材料收缩应力的数值模拟

依据SiC晶须增强树脂基复合材料的光固化实验结果，运用材料的温度应力原理，利用降温等效体积应变与光固化体积收缩率关系的假设，建立了有限元模型。研究并分析了树脂基体中组分配比、光固化层厚和晶须增强体对成型件收缩应力的影响。结果表明：树脂基体中组分配比和晶须增强体对收缩应力的影响很大，而光固化层厚对收缩应力的影响较小。     

光敏聚氨酯丙烯酸酯固化收缩应力的影响因素

光敏聚氨酯丙烯酸酯体系的光固化速度快,然而快速的聚合动力学会导致树脂在光聚合过程中内应力释放受到阻碍,出现严重的聚合收缩现象,使体系双键转化率降低,光固化材料性能较差。为了了解性能与聚合过程之间的关系,文中采用中红外光谱仪和光流变仪相结合的技术来监测光敏聚氨酯丙烯酸酯(PUA)的光聚合过程。结果发现,引发剂含量增加可以提高固化速率,降低聚合过程中的法向应力;UV光强降低会减少收缩应力,但同时也会降低体系的双键转化率。当单体官能度增加,凝胶点推迟出现,收缩应力降低。随着稀释剂单体中乙氧基柔性链增加,固化材料的柔韧性增大,从而收缩应力降低。     

固化度与固化收缩对非对称复合材料层合板固化变形的影响

采用三维有限元方法研究复合材料非对称层合板在热载荷和固化收缩载荷下的固化变形情况, 建立了材料力学特性、 固化体积收缩量和温度与固化度之间的函数关系, 考察了层合板变形曲率与温度和固化度之间的关系。数值计算结果表明: 非对称层合板变形曲率与固化终止时固化度有密切关系; 固化变形主要发生在降温阶段; 固化收缩对层合板变形曲率影响很小, 主要发生在第二个保温平台的前半段。      

混杂光固化3D打印树脂固化动力学性能

以环氧树脂(EPON828)和聚氨酯丙烯酸酯(RJ429)为基础树脂,采用自由基-阳离子混杂光固化体系来制备可用于3D打印的混杂光固化树脂,研究固化过程中自由基和阳离子光引发剂的种类、质量配比和加入量对光固化树脂固化动力学及其力学性能与成型精度的影响。结果表明:阳离子光引发剂Gencure 842和自由基光引发剂Doracur 1173为最佳复配引发剂,最佳质量比为0.75∶1,最优加入量为6.0%(质量分数);环氧树脂828和聚氨酯丙烯酸酯429的最佳质量比为1∶1,混杂光固化树脂的黏度为50.5Pa·s;光固化制品的拉伸强度和冲击强度分别为6.60MPa和8.28kJ·m~(-2),体积收缩率和翘曲度分别为-3.986%和3.62%,满足3D打印光敏树脂的成型要求。     

SL法用光固化树脂中聚合物填充剂对收缩性影响研究

本文用聚合物填料对SL用光敏树脂进行改性处理 ,研究了填料量对树脂粘度、密度、固化速度 ,以及对固态聚合物密度、线收缩、和体收缩的影响 ,并经激光快速成型机验证 ,获得了一种用于激光快速成型的实际可行低收缩性光敏树脂     

混杂紫外光固化胶黏剂的研制

合成了既有自由基固化基团(丙烯酸酯双键)又有阳离子固化基团(环氧基团)的丙烯酸环氧单酯,用红外光谱表征了合成产物并分析了自由基-阳离子混杂紫外光固化过程特征吸收峰的变化.研究了不同的稀释剂对自由基光固化和自由基-阳离子混杂光固化的凝胶率、固化体积收缩率和黏接强度的影响,结果表明:自由基-阳离子混杂光固化体系体积收缩率有明显降低,黏接强度有较大提高.     

不饱和聚酯树脂的原位同时增韧和降收缩研究

不饱和聚酯树脂(UPR)的应用非常广泛，但是由于其固化收缩率高和固化物韧性差，使其应用受到了影响。文中在总结大量增韧和降收缩研究的基础上，合成了一系列添加剂，可以同时起到增韧和降收缩的作用。除此之外，还考察了同时增韧和降收缩的UPR体系的其它力学性能和热性能以及微观形貌。将合成的添加剂与商品降收缩剂H-870的效果进行了综合比较，结果表明，QS-MB不仅有很好的增韧作用，而且可作为低收缩剂使用，而后者则不具增韧效果。     

光固化胶粘剂的研制

采用环氧丙烯酸树脂制备光固化胶粘剂,研究了胶粘剂各组分含量、引发剂配比、引发剂含量对固化时间和粘接强度的影响,得到了一种具有优良光固化性能和粘接强度的光固化胶粘剂.     

丙烯酸环氧单酯的合成及光-热固化性能

以环氧树脂和丙烯酸为原料,合成了既可以光固化也可以热固化的丙烯酸环氧单酯,用FT-IR表征了合成产物以及光-热固化过程特征吸收峰的变化.研究了不同的稀释剂对光固化和光-热联合固化的凝胶率、吸水率、力学性能和热性能的影响,测试结果表明,光固化膜凝胶率低,柔韧性好,光-热固化以后断裂强度增大.     

非收缩共聚环氧树脂基体固化的反应动力学

用FT—IR和DSC研究了非收缩共聚环氧树脂基体的固化过程,得到了膨胀性单体NSOC和环氧树脂E51的反应动力学参数及其共聚的表现动力学参数,并且得到了共聚树脂的固化时间与固化温度,贮存时间与贮存温度的关系曲线。这对树脂的实际应用和固化工艺的选择有重要的意义。理论处理的结果表明,固化时树脂基体的体积膨胀可能降低反应的活化能。     

改性不饱和聚酯树脂的形态和性能

不饱和聚酯树脂(UPR)由于固化收缩率大和固化物韧性差而影响了它的广泛应用,继合成了同时具有增韧和降收缩效果的添加剂PMB后,本文研究了添加剂的分子量和用量、添加改性后UPR体系的固化工艺及不同UPR基体树脂等因素对固化物的微现形态和性能的影响。结果表明,PMB在多种UPR中都可以产生明显的第二相结构,PMB的分子量和用量都存在一个增韧效果的最佳值,较高的固化温度有利于第二相结构的产生。     

Characterization method of photopolymerization kinetics of two dental composite resins using two types of light sources

The aim of this study was to characterize to photopolymerization curves of two dental composite resins (Z100^® from 3M ESPE Corp., and Tetric^® Ceram^® from Ivoclar Vivadent Corp.) according to the time exposure, the curing mode and the type of light source (halogen versus light emitting diode light curing units). The behavior and durability of composite resin do not depend only on their global shrinkage but also on their kinetic of polymerization which was studied with a mercury dilatometer. Four characteristics could be highlighted: the initial dilatation peak, the angle formed by the initial drop of shrinkage with the vertical axis, the angle formed by the secondary drop of shrinkage with the vertical axis and the intersection point between the two drops of shrinkage. The temperature rise was studied using a thermocouple to determine the position of the temperature peak in regard to the dilatation peak of the shrinkage curve. This is of interest for the clinical use of dental resin and light sources as well as curing procedures.     

Shrinkage properties of a modified dental resin composites containing a novel spiro-orthocarbonate expanding monomer

ObjectivesThis study investigated the photopolymerization-induced shrinkage properties of conventional methacrylate-based composites modified by a novel spiro-orthocarbonate (SOC) expanding monomer.MethodsThe epoxy monomer and SOC expanding monomer were added to a methacrylate-based resin matrix at five different ratios ranging from 20 wt.% (SOC + Epoxy) (group 1) to 60 wt.% (SOC + Epoxy) (group 5). Volumetric shrinkage and contraction stress developing after polymerization were measured using X-ray micro-computed tomography and a universal testing machine, respectively.ResultsThe volumetric shrinkage of the resin composite samples ranged from 0.92% (group 5) to 3.85% (control group) 30 min after light curing. Group 5 had the lowest volumetric shrinkage (p < 0.05), followed by groups 4, 3, 2 and 1. The contraction stress of the materials ranged from 1.86 MPa (group 5) to 3.56 MPa (control group). The lowest contraction stress was also observed in group 5, 30 min after curing (p < 0.05).ConclusionIncluding SOC expanding monomer reduced volumetric shrinkage and contraction stress of composites in comparison with conventional methacrylate-based composites.     

Drying shrinkage of expansive cements

Drying shrinkage behaviour of expansive cement pastes were studied and compared with those of portland cements. Results indicate that the shrinkage behaviour of these two cements is significantly different from each other. Generally, expansive cements shrink more than portland cements, and especially more so if they have not been adequately cured, i.e. curing period of at least 7 days is necessary to ensure good performance against shrinkage. Internal damage caused by large amounts of expansion leads to a large magnitude of shrinkage. In that event curing does not seem to have any beneficial impact on shrinkage performance. Steel reinforcement also seems to decrease shrinkage magnitude, but it has no effect on the shrinkage characteristic. Much of the research on expansive cements has so far been focused on the expansion behaviour rather than on the shrinkage behaviour. More research on shrinkage is needed to improve its field performance.     

Mitigation of autogenous shrinkage in alkali activated slag mortars by internal curing

Alkali activated slag shows considerable promise as an environmentally friendly alternative to binders produced from ordinary portland cement. The shrinkage behavior of alkali activated slags, however, is not well understood, and is a hurdle to widespread adoption. The use of pre-wetted lightweight aggregate-based internal curing to mitigate shrinkage in slags activated by Na₂CO₃ solution or waterglass/NaOH solution has been investigated. Chemical shrinkage measurements were used to determine the amount of additional curing water needed by the mixtures, and autogenous and total shrinkage measurements used to determine the effects of internal curing on the overall shrinkage of the systems. Internal curing can completely mitigate autogenous shrinkage; however, in the systems examined here, drying shrinkage was the dominant shrinkage factor. In such a case, the benefits of internal curing are most clearly observed during the first 7 days.     

Influence of hydrogen bonding on properties of BIS-GMA analogues

The influence of chemical structure on the important properties of composite matrix resins is being systematically investigated. This study addresses the relationships between pendent side chain structures, viscosity and curing shrinkage. In particular, viscosity is known to be greatly influenced by intermolecular interactions, such as hydrogen bonding, and free volume effects. In order to establish the relative importance of these factors, analogues of BIS-GMA were synthesized in which the pendent hydroxyl groups were replaced by trimethyl siloxyl, and by dimethyl, isopropyl siloxyl groups. The viscosities were determined with a cone and plate viscometer and curing shrinkages were determined gravimetrically. They were compared to previously determined values for BIS-GMA and its methyl and hydrogen substituted analogues. The high viscosity of BIS-GMA is drastically reduced by replacement of the hydroxyl group, or its substitution by silylation. The relatively smaller effects produced by varying the bulk of the substituted side chains indicates that the main effect on viscosity is due to the presence or absence of hydrogen bonding. Conversely, increasing the bulk of the side chain substituent has less effect on viscosity, but significantly reduces the curing shrinkage. Changes in curing shrinkages were explained in terms of effects of free volumes associated with the monomers.     

Accelerated microwave curing of concrete: A design and performance-related experiments

Microwave (MW)-accelerated curing has emerged as an innovative and popular curing method for concrete materials. This paper reports the results of a study to model the horn antenna used for the MW irradiation of a workpiece with a mobile MW-accelerated concrete curing unit, based on a coupled thermal and electromagnetic analysis. The mathematical models were useful for evaluating the heat generation within a horn antenna and as a basis for constructing a mobile MW-accelerated curing unit with an operating frequency of 2.45 GHz and a MW power level of 800 W. Further, the early-age compressive strength development and volume stability of MW-cured concrete were investigated in terms of its shrinkage and compared to the properties of autoclave-cured concrete. The design results showed that under the concept of the allowable maximum temperature for the concrete workpiece, which was controlled to less than 80 °C, a horn antenna that was 216.70 mm wide, 333.68 mm long, and 273.0 mm high produced a uniform thermal distribution in a concrete workpiece. Moreover, experimental investigations showed that the application period for curing using a mobile MW-curing unit was considerably shorter than that in autoclave curing methods. The appropriate delay time (time after concrete mixing) was 30 min, and MW irradiation for 45 min could improve the maximum 8-h early-age compressive strength of MW-cured concrete, whereas an application time of 15 min produced the 28-day compressive strength. When a concrete workpiece was cured at high temperature using MW energy for more than 15 min at a temperature greater than 80 °C, the effect was a continuous increase in the early-age compressive strength, which was greater than that achieved by autoclave curing. In terms of volumetric stability, MW-curing for 30 and 45 min increased the ultimate shrinkage to a greater extent than that by autoclave curing and vice versa in the case of a MW application time of 15 min.     

热养护过程中超高性能混凝土的收缩性能研究

热养护能够提高UHPC的强度和减小UHPC的干燥收缩,已经广泛应用于工程实践中。主要研究了UHPC在热养护过程中的收缩变形性能和不同热养护龄期下UHPC的微观结构。结果表明,在热养护过程中,UHPC在50℃以内基本不发生收缩,当温度接近70℃时,收缩值迅速增加,最终的收缩值为450×10-6;随着配筋率的提高,UHPC在热养护过程中的收缩减小。热养护后,基体变得致密,Ca(OH)2的含量大幅减少,水化程度大大提高。     

黏结剂相对分子质量对浇注PBX固化应力的影响?

采用自行研制的固化应力测试装置,测量了端羟基聚丁二烯(HTPB)基浇注高聚物黏结炸药(PBX)固化过程的应力变化,计算出固化应力数据,分析了黏结剂相对分子质量对热固性浇注PBX固化应力的影响,并对其在不同固化温度下的黏结强度进行了测试。结果表明:同一固化温度时,随着HTPB相对分子质量的逐渐增大,浇注PBX在固化阶段的最大热应力及收缩应力都逐渐减小。固化温度为100℃时,相对分子质量为1 500、2 800、4 000的HTPB基固化物因固化反应所产生的最大热应力分别为2.14、1.12、1.01 MPa,最大收缩应力分别为0.29、0.22、0.15 MPa。在固化降温阶段,HTPB相对分子质量越大,浇注PBX的收缩应力也越大。HTPB相对分子质量相同时,固化物的黏结强度随着固化温度的升高而降低;而固化温度一定时,HTPB相对分子质量对浇注PBX的黏结强度影响不大。     

Enhancing the performance of calcium sulfoaluminate blended cements with shrinkage reducing admixture or lightweight sand

This study investigates the effect of using shrinkage reducing admixture (SRA) or lightweight sand (LWS) on enhancing the performance of calcium sulfoaluminate (CSA) cement in combination with ordinary Portland cement (OPC). Of special interest is the efficacy of the SRA or LWS in modifying the expansion/shrinkage and compressive strength characteristics of OPC-CSA systems in the absence of adequate duration of water curing, which is critical for the expansive reaction of CSA cement and its ability to mitigate shrinkage. Hydration kinetics, autogenous and drying deformation, thermogravimetry, and scanning electron microscopy (SEM) are used to evaluate the effect of SRA or LWS on the performance of the OPC-CSA systems. Test results indicate that the OPC-CSA system can exhibit similar drying shrinkage to that of the plain OPC mixture when no moist curing is applied. In the presence of LWS or SRA, the OPC-CSA systems exhibited lower shrinkage or higher extent of expansion compared to the corresponding OPC-CSA mixture alone. This is attributed to delay of the drop in internal relative humidity and promoting hydration of the OPC-CSA system which can enhance the ettringite-generating potential of CSA cement. The use of LWS was found to be highly effective in enhancing compressive strength of OPC-CSA system. SEM results at 91 days confirm the higher density and lower porosity for the paste surrounding LWS particles compared to the corresponding mixture made without LWS. In the case of inadequate moist curing, the presence of LWS or SRA is shown to enhance the overall performance of OPC-CSA system. For a given overall desirability value of 0.65 determined by multi-objective optimization, the incorporation of 1% SRA or 10% LWS was found to enable the reduction the required period of moist curing from 6 days to 5 and 3 days, respectively.