A facile rheological approach for the evaluation of “super toughness point” of compatibilized HDPE / MWCNT nanocomposites

Fast and efficient determination of the optimal mechanical property of a polymer/CNT nanocomposite is crucial to develop polymer conductive nanocomposites. This work establishes a rheological approach to evaluate the super-toughness point of compatibilized high density polyethylene (HDPE)/multi-walled carbon nanotube (MWCNT) nanocomposites. Results illustrate that three types of HDPE/MWCNT nanocomposites exhibit obvious gel plateaus in the dynamic rheological curves and the gel points of nanocomposites with compatibilizer shift to the low MWCNTs loading. The super-toughness points of HDPE/MWCNT nanocomposites with compatibilizers show the correspondence with the gel points acquired from the rheological data, indicating that dynamic rheology is an effective way to determine the super-toughness points of HDPE/MWCNT nanocomposites with compatibilizers. Furthermore, unique network structure at the gel points is directly observed and the new mechanism of toughness is proposed. This study provides new insights for effective control of the structures and properties of polymer/CNT nanocomposites.     

Comparison of microstructure and mechanical properties of ultra-narrow gap laser and gas-metal-arc welded S960 high strength steel

The microstructural characteristics and mechanical properties, including micro-hardness, tensile properties, three-point bending properties and Charpy impact toughness at different test temperatures of 8 mm thick S960 high strength steel plates were investigated following their joining by multi-pass ultra-narrow gap laser welding (NGLW) and gas metal arc welding (GMAW) techniques. It was found that the microstructure in the fusion zone (FZ) for the ultra-NGLW joint was predominantly martensite mixed with some tempered martensite, while the FZ for the GMAW joint was mainly consisted of ferrite with some martensite. The strength of the ultra-NGLW specimens was comparable to that of the base material (BM), with all welded specimens failed in the BM in the tensile tests. The tensile strength of the GMAW specimens was reduced approximately by 100 MPa when compared with the base material by a broad and soft heat affected zone (HAZ) with failure located in the soft HAZ. Both the ultra-NGLW and GMAW specimens performed well in three-point bending tests. The GMAW joints exhibited better impact toughness than the ultra-NGLW joints.     

Some results related to the toughness of 3-domination critical graphs

A graph G is said to be k-γ-critical if the size of any minimum dominating set of vertices is k, but if any edge is added to G the resulting graph can be dominated with k−1 vertices. The structure of k-γ-critical graphs remains far from completely understood, even in the special case when the domination number γ=3. In a 1983 paper, Sumner and Blitch proved a theorem which may regarded as a result related to the toughness of 3-γ-critical graphs which says that if S is any vertex cutset of such a graph, then G−S has at most |S|+1 components. In the present paper, we improve and extend this result considerably.     

Fabrication of a high-strength hydrogel with an interpenetrating network structure

Hydrogels have potential applications in many fields, but the poor mechanical strength has limited their further development. In this article, we designed a high-strength hydrogel with an interpenetrating network (IPN) structure from polyacrylamide (PAM) and poly(vinyl alcohol) (PVA). Synthesis parameters, such as PVA/AM mass ratio, crosslinker dosage and elongation time were carried out for high tensile strength and elongation. The results showed that chemical crosslinking, physical entanglement and PVA precipitates were the dominant parameters for the improvement of mechanical properties. The PVA structure transferred from crystal to amorphous due to intermolecular and intramolecular interactions (such as hydrogen bond and self-crosslinking). PVA precipitates scatterred in the brittle PAM matrix homogeneously which dispersed the applied stress and improved the hydrogel toughness. The tensile strength and elongation were extremely high, they were 2.4 MPa and 3100%, respectively. The simple method is versatile in synthesizing high-strength IPN hydrogels using many kinds of polymer species.     

Rubber toughening of poly(ether imide) by modification with poly(butylene terephthalate)

Rubber toughening of poly(ether imide) (PEI) has been elusive up to now due to the high processing temperature of PEI, which leads to degradation of the rubber. In this study, by profiting from the miscibility between PEI and poly(butylene terephthalate) (PBT), and the low T_g of PBT, we prepared a blend by melt extrusion with 20 wt% PBT in an attempt to render it toughenable by decreasing its T_g and processing temperature. The PEI-rich blend was subsequently mixed with maleic anhydride (0.9 wt%) grafted poly(ethylene-octene) copolymer (mPEO) up to 30 wt%. The decrease in T_g and processing temperature resulted in no observable degradation of the mPEO, and to the formation of a homogeneous morphology of rubber particles with a fine particle size, indicating that compatibilization was achieved. Upon rubber addition, stiffness decreased, while a very large toughness increase occurred with only 15% mPEO (impact strength more than 10-fold that of the PEI-PBT matrix). Upon observation of the fracture surface, the increase in impact strength was attributed partially to the cavitation and debonding of the rubber particles, and mostly to the deformation and yielding of the PEI-PBT matrix.     

Effect of nucleating agent on the structure and properties of polypropylene/poly(ethylene-octene) blends

The effect of the sorbital nucleating agent on properties of the ethylene-octene copolymer (POE) toughened polypropylene (PP) was studied. The results show that the addition of POE increases notched Izod and Charpy impact strength significantly but impair the tensile strength and flexural modulus. As a nucleating agent (1,3,2,4-di(p-methylbenzylidene) sorbitol, DM) was added, the toughness and stiffness of toughed PP increased simultaneously at the same content of POE. This result shows that the toughness and stiffness of toughed PP are in balance. Polarized light microscopy analysis shows that with the addition of POE and nucleating agent, only a low level of PP spherulites were observed.     

层状仿生高分子纳米复合材料

自然界中,鲍鱼壳具有有机-无机多级次层状结构以及大量的复合界面作用,力学性能优异。这一独特的层状结构主要由霰石碳酸钙片层构成,并通过体积分数约为5%的生物高分子在层间进行粘合。受鲍鱼壳这一微观结构的启发,我们利用不同的基元材料如纳米蒙脱土、碳纳米管以及氧化石墨烯等构筑仿鲍鱼壳层状结构,并结合多种界面设计,实现不同界面、不同基元材料之间的协同作用,得到了力学性能优异的高分子纳米复合材料。仿生高分子纳米复合材料的成功制备,为今后的研究提供了崭新的思路,拓宽了高分子纳米复合材料的应用前景。     

J-integral evaluation of nanoclay-modified HDPE/PA6 microfibrillar composites

Microfibrillar composites (MFC) are polymer-polymer composites with many advantages, including good dispersion and bonding of in-situ generated fibrils. Recently, it has been shown that their performance can be enhanced by suitable addition of organophilized montmorillonite (oMMT) provided the numerous oMMT-induced effects are harmonized. This work deals with evaluation of resistance against unstable crack propagation (J-integral) in combination with Charpy and tensile impact strength methods, and SEM observation of fibrils shape and size and fracture surfaces. The results indicate that addition of PA6 inclusions and oMMT to relatively ductile HDPE reduces toughness evaluated using Charpy and J-integral. The fact that tensile impact strength is not reduced by oMMT indicates the importance of the impact testing mode for MFC. Of importance is the fact that formation of PA6 fibres reinforced with oMMT practically does not reduce toughness. Hence, the drawn oMMT-modified system with significantly higher stiffness and practically unchanged fracture resistance can be obtained. Combination of the complex effect of oMMT and in-situ fibrils reinforcement present a tool to attain polymer systems with enhanced well-balanced properties.     

SUPER TOUGH GELS WITH A DOUBLE NETWORK STRUCTURE

 Living tissues work with fantastic functions in soft and wet gel-like state. Thus, hydrogels have attracted much attention as excellent soft & wet materials, suitable for making artificial organs for medical treatments.However, conventional hydrogels are mechanically too weak for practical uses. We have created double network (DN) hydrogels with extremely high mechanical strength in order to overcome this problem. DN gels are interpenetrating network (IPN) hydrogels consisting of rigid polyelectrolyte and soft neutral polymer. Their excellent mechanical properties cannot be explained by the standard fracture theories. In this paper, we discuss about the toughening mechanism of DN gels in accordance with their characteristic behavior, such as large hysteresis and necking phenomenon. We also describe the results on tissue engineering application of DN gels.     

酚醛树脂的增容作用对聚甲醛/丁腈橡胶共混物的韧性、结晶形态和亚微相态的影响

考察了酚醛树脂(Novolak)的增容作用对聚甲醛(POM)/丁腈橡胶(NBR)共混物的韧性、结晶形态和亚微相态的影响.实验结果表明,POM与NBR不相容,直接共混不能提高POM的韧性;添加Novolak后,当NBR质量分数为40%时共混物发生“脆-韧”转变.POM/NBR共混物中POM球晶尺寸大,易形成应力集中点,导致增韧效果不佳;Novolak可通过与POM的分子链间相互作用,改变POM分子链固有的规程和排列方式,使球晶显著减小.亚微相态显示,POM/NBR呈现“海-岛”结构相态,NBR在基体中分散性很差;添加Novolak可提高NBR在基体中的分散性;当NBR质量分数达到40%时,NBR在基体中呈现带状网络结构.网带结构能够终止受外力作用而在基体中产生的银纹和剪切屈服,增加了共混物的破裂能,从而使共混物的韧性显著提高.