Thermodynamic and mechanical properties of amine-cured epoxy resins using group interaction modelling

The prediction of thermal and mechanical properties of amine-cured epoxy resins by group interaction modelling is presented. The derivation of the group interaction based approach to the prediction of macroscopic engineering properties of both linear and crosslinked epoxy resins is described with specific application to MY721 resin. The glass transition temperature, bulk and tensile modulus and linear thermal expansion coefficient of tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) cured with 4,4′-diaminodiphenyl sulphone (DDS) are estimated using the model and compared with results from dynamic mechanical experiments. The glass transition of TGDDM/DDS is calculated to occur at approximately 248 °C and the reasons for a secondary peak in the spectrum cured to 180 °C are given. The bulk and tensile modulus of TGDDM/DDS are calculated to be 7.54 GPa and 5.34 GPa, respectively.     

High-Performance Polymeric Materials through Hydrogen-Bond Cross-Linking

It has always been critical to develop high-performance polymeric materials with exceptional mechanical strength and toughness, thermal stability, and even healable properties for meeting performance requirements in industry. Conventional chemical cross-linking leads to enhanced mechanical strength and thermostability at the expense of extensibility due to mutually exclusive mechanisms. Such major challenges have recently been addressed by using noncovalent cross-linking of reversible multiple hydrogen-bonds (H-bonds) that widely exist in biological materials, such as silk and muscle. Recent decades have witnessed the development of many tailor-made high-performance H-bond cross-linked polymeric materials. Here, recent advances in H-bond cross-linking strategies are reviewed for creating high-performance polymeric materials. H-bond cross-linking of polymers can be realized via i) self-association of interchain multiple H-bonding interactions or specific H-bond cross-linking motifs, such as 2-ureido-4-pyrimidone units with self-complementary quadruple H-bonds and ii) addition of external cross-linkers, including small molecules, nanoparticles, and polymer aggregates. The resultant cross-linked polymers normally exhibit tunable high strength, large extensibility, improved thermostability, and healable capability. Such performance portfolios enable these advanced polymers to find many significant cutting-edge applications. Major challenges facing existing H-bond cross-linking strategies are discussed, and some promising approaches for designing H-bond cross-linked polymeric materials in the future are also proposed.     

Morphology, dynamic mechanical and thermal studies on poly(styrene-co-acrylonitrile) modified epoxy resin/glass fibre composites

Poly(styrene-co-acrylonitrile) (SAN) was used to modify diglycidyl ether of bisphenol-A (DGEBA) type epoxy resin cured with diamino diphenyl sulfone (DDS) and the modified epoxy resin was used as the matrix for fibre reinforced composites (FRPs) in order to get improved mechanical and thermal properties. E-glass fibre was used as the fibre reinforcement. The morphology, dynamic mechanical and thermal characteristics of the systems were analyzed. Morphological analysis revealed heterogeneous dispersed morphology. There was good adhesion between the matrix polymer and the glass fibre. The dynamic moduli, mechanical loss and damping behaviour as a function of temperature of the systems were studied using dynamic mechanical analysis (DMA). DMA studies showed that DDS cured epoxy resin/SAN/glass fibre composite systems have two T_gs corresponding to epoxy rich and SAN rich phases. The effect of thermoplastic modification and fibre loading on the dynamic mechanical properties of the composites were also analyzed. Thermogravimetric analysis (TGA) revealed the superior thermal stability of composite system.     

颗粒Al_2O_3增强环氧树脂复合材料的微波固化动力学及性能

利用Avrami法研究了Al_2O_3颗粒及其添加量对E51/DDS体系的微波固化表观活化能的影响,采用差示扫描量热、动态力学分析、力学性能测试和扫描电子显微镜等试验手段对产物的热性能、力学性能及微观形态进行研究。结果表明,Al_2O_3颗粒增强E51/二氨基二苯砜(DDS)体系可以显著降低其微波固化的反应活化能,其中相比于未添加的体系,添加量达到40%时,其微波固化活化能降低了19.3%;加入Al_2O_3颗粒可以提高体系的玻璃化转变温度,增加幅度与添加量正相关;且体系的损耗模量随着添加量的增加而降低。拉伸和弯曲模量随着Al_2O_3添加量的增加而增加,而拉伸和弯曲强度则呈现先增加后减小的趋势。断面分析表明Al_2O_3颗粒的存在阻止了微裂纹的扩展,消耗更多的能量,提高了浇注体的力学性能。     

树枝形聚合物/线性聚合物共混的研究进展

综述了国内外有关树枝形聚合物／线性聚合物共混物的形态结构、热性能、动态力学性能、流变性能和物理力学性能的研究进展，树枝形聚合物因其独特的结构和性能特点，可作为聚合物的加工助剂、流变学改性剂、增容剂以及增强或增韧剂。     

明胶/海藻酸钠(京尼平交联)互穿网络膜的制备与性能

为了提高海藻酸钠与明胶各自的性能,首先,以海藻酸钠和明胶为原料,以京尼平、CaCl2为交联剂,采用分步交联法制备了明胶/海藻酸钠互穿网络膜。然后,利用FTIR对明胶/海藻酸钠互穿网络结构进行了表征与分析,根据FTIR结果推测了互穿网络结构形成的机制。最后,探讨了京尼平的加入量和明胶与京尼平的质量比对互穿网络膜力学性能和交联度的影响,及海藻酸钠与明胶的质量比对互穿网络膜力学性能、断面形貌、热稳定性和吸水保水性能的影响。结果表明:当明胶与京尼平的质量比为200∶1、海藻酸钠与明胶的质量比为2∶1时,互穿网络膜具有最佳的力学性能、吸水保水性能和相容性;此外,互穿网络膜的力学性能也优于纯海藻酸钠膜与纯明胶膜的。明胶的加入提高了互穿网络膜在低温区的热稳定性,但降低了高温区的热稳定性。海藻酸钠与明胶之间可能以分子间作用力、氢键及离子键等相互作用,提高了二者各自的初始分解温度与最大热分解温度。研究解决了海藻酸钠与明胶力学性能差的问题,为拓展海藻酸钠在医用领域的应用提供参考。     

Molecular dynamics study of binding energies, mechanical properties, and detonation performances of bicyclo-HMX-based PBXs

To investigate the effect of polymer binders on the monoexplosive, molecular dynamics simulations were performed to study the binding energies, mechanical properties, and detonation performances of the bicyclo-HMX-based polymer-bonded explosives (PBXs). The results show that the binding energies on different crystalline surfaces of bicyclo-HMX decrease in the order of (010)>(100)>(001). On each crystalline surface, binding properties of different polymers with the same chain segment are different from each other, while those of the polymers in the same content decrease in the sequence of PVDF>F(2311)>F(2314) approximately PCTFE. The mechanical properties of a dozen of model systems (elastic coefficients, various moduli, Cauchy pressure, and Poisson's ratio) have been obtained. It is found that mechanical properties are effectively improved by adding small amounts of fluorine polymers, and the overall effect of fluorine polymers on three crystalline surfaces of bicyclo-HMX changes in the order of (010)>(001) approximately (100). In comparison with the base explosive, detonation performances of the PBXs decrease slightly, but they are still superior to TNT. These suggestions may be useful for the formulation design of bicyclo-HMX-based PBXs.     

Molecular dynamics simulations of RDX and RDX-based plastic-bonded explosives

Molecular dynamics simulations have been performed to investigate well-known energetic material cyclotrimethylene trinitramine (RDX) crystal and RDX-based plastic-bonded explosives (PBXs) with four typical fluorine-polymers, polyvinylidenedifluoride (PVDF), polychlorotri-fluoroethylene (PCTFE), fluorine rubber (F(2311)), and fluorine resin (F(2314)). The elastic coefficients, mechanical properties, binding energies, and detonation performances are obtained for the RDX crystal and RDX-based PBXs. The results indicate that the mechanical properties of RDX can be effectively improved by blending with a small amount of fluorine polymers and the overall effect of fluorine polymers on the mechanical properties of the PBXs along three crystalline surfaces is (001)>(010) approximately (100) and PVDF is regarded to best improve the mechanical properties of the PBXs on three surfaces. The order of the improvement in the ductibility made by the fluorine polymers on different surfaces is (001) approximately (010)>(100). The average binding energies between different RDX crystalline surfaces and different polymer binders are obtained, and the sequence of the binding energies of the PBXs with the four fluorine polymers on the three different surfaces is varied. Among the polymer binders, PVDF is considered as best one for RDX-based PBXs. The detonation performances of the PBXs decrease in comparison with the pure crystal but are superior to those of TNT.     

Characterization of double network epoxies with tunable compositions

This article reports the processing and characterization of epoxy resins with near constant molar cross-link density prepared from sequentially reacted amine cross-linking agents. Stoichiometric blends of curing agents with compositions ranging from all polyetheramine to all diaminodiphenylsulfone (DDS) are reacted with an epoxy monomer in a staged curing procedure. The low reactivity of the aromatic amine permits the selective reaction of the aliphatic amine in the first stage. The residual aromatic amine and epoxide functionality are reacted in a second stage at higher temperature. Above approximately 50% DDS content the first stage produces sol glasses which have not reached the gel point. The glass transition temperatures of the partially cured networks decrease monotonically with increasing DDS content. The partially cured networks can be characterized thermally and mechanically above their respective glass transitions without significantly advancing the reaction of the residual DDS and epoxide functionality. The networks formed after the second stage of the cure exhibit thermal and mechanical properties intermediate between those of the two individual amine cured networks, according to composition. The blends do not show any evidence of phase separation across the entire composition range in either the partially cured or fully cured state.     

The effect of particle shape on the mechanical properties of filled polymers

The existing models for predicting the elastic moduli of polymers dispersed with particles of shape other than spheres and continuous fibres are reviewed. The applicability and limitation of these equations are discussed. The emphasis of the review is to seek a unified understanding and approach to the effect of particle shape at finite concentration on the elastic moduli, thermal expansion coefficient, stress concentration factor, viscoelastic relaxation modulus and creep compliance of filled polymers. The effects of anisotropic particle shape on mechanical properties of polymeric composites are clearly illustrated. Attention is also drawn to the relationship between elastic moduli, thermal expansion, creep elongation and stress relaxation moduli.     

脲键和氨酯键对嵌段聚氨酯和嵌段聚脲微相分离影响的研究

本文研究了脲键和氨酯键对溶液聚合的四种聚氨酯、聚脲模型化合物性质的影响。用DSC,DMS研究了在相界面或在硬段微区不同键对聚合物热学和动态力学性质的影响。较高极性的脲键给聚合物提供了较强的氢键和较好的热稳定性,并使这些聚合物在橡胶平台区有较高和变化较小的动态剪切模量。这可用脲键比氨酯键有较好的相分离和较高的熔化温度来说明。     

Polymere Nanoverbundwerkstoffe: Chancen,Risiken und Potenzial zur Verbesserung der mechanischen und physikalischen Eigenschaften

Polymer Nanocomposites: chances, risks and potential to improve the mechanical and physical properties The development of nano‐particle reinforced polymer composites is presently seen as one of the most promising approaches of materials for future engineering applications. The unique properties of at least some types of the nano‐particles (e.g., Carbon Nanotubes or Carbon Black) and the possibility of combining them with conventional materials and reinforcements (e.g., carbon‐, glass‐ or aramid‐fibres), has led to an intense research in the field of nanocomposites. Especially Carbon Nanotubes have shown a high potential for an improvement of the properties of polymers. Besides an increase in the electrical conductivity even at an extremely low nanotube content the improvement of the mechanical properties is of special interest. The exceptionally high aspect ratio in combination with a low density and a high strength and stiffness make the carbon nanotubes a most interesting candidate for a reinforcement of polymeric materials. The electrical, mechanical and thermal properties of Carbon Nanotubes open up new perspectives also for their use as multifunctional materials, e.g. conductive polymers with improved mechanical performance. The problem, however, is to transfer the interesting potential regarding the mechanical, thermal and electrical properties to the polymer. Two main issues have to be addressed for a significant improvement of the properties of polymers by adding Carbon Nanotubes: the interfacial bonding and, especially also, a proper dispersion of the individual Carbon Nanotubes in the polymeric matrix.     

Preparation and characterization of epoxy nanocomposites by using PEO-grafted silica particles as modifier

EP/SiO₂ nanocomposites, which contained PEO flexible chain, have been prepared via epoxy resin and PEO-grafted silica particles. The PEO-silica particles were obtained by endcapping PEO-1000 with toluene 2,4-diisocyanate (TDI), followed by a reaction with silica sols. The chemical structure of the products was confirmed by IR measurements, and the mechanical properties of composites such as impact strength, flexural strength, dynamic mechanical thermal properties were investigated. The results showed that the addition of the PEO-grafted silica particles to the epoxy/DDS curing system, the impact strength is 2 times higher than that of the neat epoxy. While the storage modulus and the glass transition temperature are a little changed. The morphological structure of impact fracture surface and the surface of the hybrid materials were observed by scanning electron microscope (SEM) and atomic force microscopy (AFM), respectively.     

Review of modern techniques to generate antireflective properties on thermoplastic polymers

Modern optical applications need solutions for providing polymer surfaces with antireflective properties. The problems involved in coating comprise thermal limitations, incompatible mechanical properties of coating and substrate materials, and interaction between polymers and plasma. As an alternative for coating, antireflective properties on polymers can also be obtained by hot embossing or by ion etching of surface structures. My objective is to provide the criteria for choosing suitable deposition or structuring methods based on an understanding of plasma-, radiation-, and ion-induced surface phenomena; material compatibility; mechanical and environmental performance; and cost issues. The potential to produce antireflective interference coatings is documented for plasma-enhanced physical- and chemical-vapor-deposition methods, including modern hybrid techniques, as well as for solgel wet-chemical processes. The review about state-of-the-art coatings focuses on the thermoplastic acrylic, polycarbonate, and cycloolefin polymers.     

聚醚醚酮及其共混物的研究EI

综述了高性能树脂聚醚醚酮及其共混物的研究现状，讨论了聚醚醚酮的形态结构、结晶和熔融双峰行为及力学性能的研究，指出了共混物的分子结构对相容性、形态结构及力学性能的影响，说明共混使所得高分子材料的性能更多样化。     

环氧树脂低聚物原位增容PA66/TLCP共混物

用环氧树脂低聚物作界面增容剂,熔融挤出法制备了PA66/TLCP共混物。通过拉伸、弯曲等力学性能测试并结合热失重(TG)分析,结果表明:环氧树脂低聚物增容后的共混物力学性能、热稳定性均有显著提高。共混物断面SEM扫描结果表明,由于环氧树脂低聚物界面增容作用,分散相TLCP在基体PA66中的分散性提高并且相畴尺寸减小。加工流变学测试和红外光谱显示,环氧树脂低聚物与基体树脂PA66和分散相TLCP分子在熔融加工过程中原位发生化学反应,环氧树脂低聚物在共混物界面起到桥的作用。     

Biocomposites based on cellulose acetate and short curauá fibers: Effect of plasticizers and chemical treatments of the fibers

Biocomposites based on cellulose acetate and short curauá fibers were prepared by extrusion on a laboratory scale. The influence on the mechanical and thermal properties of the biocomposites caused by three different plasticizers, dioctyl phthalate (DOP), triethyl acetate (TEC) and glycerol triacetate (GTA), and the chemical treatment of the fibers was evaluated. The fibers were mercerized or extracted with acetone. The efficiency of the plasticizers was determined by their molecular features, however, for some applications DOP can be replaced by less hazardous plasticizers, such as TEC and GTA. The biocomposites presented morphology of fibrils uniformly dispersed in the polymer matrices and higher Young’s modulus, higher thermal dimensional stability and lower thermal conductivity in comparison with the properties of the corresponding plasticized polymer matrices. Moreover, these biocomposites combine mechanical and dimensional properties of dense materials with thermal conductivities of porous and thermally insulating polymers.     

含1,3,5-三嗪结构聚芳醚高性能聚合物的合成

1,3,5-三嗪基聚合物具有优异综合性能,但传统1,3,5-三嗪基聚合物难溶解、难熔融,通常在高温高压下才能制得高分子量聚合物,限制了其在分离膜、绝缘漆和粘合剂等领域的应用。文中基于分子设计理论,分别在聚合物分子链中引入柔性侧基、非对称性结构、扭曲或扭曲非共平面结构等,合成了系列既耐高温又可溶解的含1,3,5-三嗪结构新型聚芳醚高性能聚合物,探讨了分子结构等对聚合物溶解性、热性能和力学性能间影响规律。     

Ductile PLA nanocomposites with improved thermal stability

Polylactide (PLA) is used as a biomedical material because it is biodegradable, but the vast majority of biodegradable polymers in clinical use are composed of rather stiff materials that are unsuitable for use in numerous applications because they exhibit limited extendibility, weak mechanical strength, and poor thermal stability. We modified PLA with 2-methacryloyloxyethyl isocyanate (MOI) to prepare ductile PLA materials. By utilizing a novel sol–gel process, PLA nanocomposites were further prepared with improved mechanical properties and thermal stability. The 10% thermal decomposition temperature for PLA modified with 5% MOI and 5–10% silica was 21–32 °C higher than that of original pristine PLA. Elongation at break increased by 4–13 times when compared to neat PLA while the tensile strength was maintained at 30–40 MPa. These synthesized PLA nanocomposites can be applied as biomaterials with improved mechanical and thermal properties.