磺化乙丙橡胶离聚体的熔融流动性及力学性能

研究了不同因素包括相转移催化剂、磺化度、中和度、中和用阳离子及增塑剂等对磺化乙丙橡胶离聚体的熔融流动性及力学性能的影响。结果表明,在合适条件下可得到Ｂｒａｂｅｎｄｅｒ扭矩为３５～４０Ｎｍ、拉伸强度为２０～２８ＭＰａ、断裂伸长率为５００％～６００％、永久变形小于１０％的热塑性弹性体     

Experimental study of weldline caused by flow lead effect in gas assisted injection moulded parts

Abstract

Gas assisted injection moulding has become one of the most important methods for the manufacture of plastic products. However, there are several unsolved problems that confound the overall success of this technique. The weldline caused by the flow lead effect in the polymer melt is one of them. In this report, an L′18 orthogonal array design based on the Taguchi method has been conducted to investigate the flow lead induced weldlines in gas assisted injection moulded parts. A plate cavity with a gas channel on the side was used for moulding. Experiments were carried out on an 80 t reciprocating screw injection moulding machine equipped with a high pressure gas injection unit. After moulding, the depth of the weldline was measured. For the factors selected in the main experiments, melt injection temperature and mould temperature were found to be the principal factors affecting the weldline depth of gas assisted injection moulded parts. Experimental investigation of a gas assisted injection moulding problem can help in better understanding the weldlines caused by flow lead effects, so that steps can be taken to optimise the surface quality of moulded parts. PRC/1755     

Melt flow and mechanical properties of sulfonated butyl rubber ionomers

Study of melt flow properties and mechanical properties of sulfonated butyl rubber ionomers showed that in the case of lithium ionomers addition of zinc stearate lowered obviously the melt viscosity, represented by torque value of a Brabender rheometer, and enhanced tensile strength of the ionomer up to 25% of zinc stearate, while in the case of ethylamine neutralized ionomer addition of zinc stearate lowered the melt viscosity not so obviously as in the case of lithium ionomer and slightly affected the tensile strength. Amine neutralized ionomers exhibited very low permanent sets, while the lithium ionomer showed much higher permanent set, which increased with sulfonate group and amount of zinc stearate added. Increase of neutralization degree below equivalent ratio of 1 significantly raised the melt viscosity and tensile strength. For monovalent cation ionomer, melt viscosity and tensile strength diminished with decreasing ionic potentials, but for divalent cation ionomers with increasing ionic potentials and with decreasing covalent character tensile strength decreased and melt viscosity increased. For different amine neutralized ionomers tensile strength decreased in the following orders: ethylamine > triethylamine > diethylamine; isopropylamine > ethylamine > tertiary butylamine > methylamine; ethylamine > hexylamine > dodecylamine > octadecylamine.     

Effects of dispersion on flow and mechanical properties of polymer blends

Blends of linear polyethylene and ethylene-propylenediene elastomer, representing the entire composition range, were prepared under various conditions of shear intensity. It was found that both viscoelastic flow parameters and mechanical properties at large deformation respond strongly to variations in shear history of material preparation. Mechanical degradation of the polymers not being detected, it is postulated that property variations are due to morphological effects related to domain sizes of the two components and to the ease of molecular diffusion across domain boundaries. Thus, mechanical properties develop over finite times of mixing, consistent with the attainment of steady states in domain sizes. Maximum sensitivity of mechanical properties to mixing variables is found for 50/50 blends of the polymers, which have maximum interdomain contact areas. It appears feasible to develop desired balances of flow and mechanical properties in such polyblends through the close control of component dispersion processes.     

Evaluation of water uptake and mechanical properties of biomedical polymers

Poly(vinyl alcohol) grafted with poly(d,l ‐lactide) or poly(d,l ‐lactide‐co‐glycolide) oligomers, were synthesized in our laboratory and investigated with respect to their potential for tissue engineering applications. In order to understand their structure–properties relationships the effect of length and composition as well as number of polyester grafts on PVA backbone chain on water uptake capability and hydrophilicity/hydrophobicity balance and on mechanical properties of hydrogels was evaluated. The E moduli of hydrogels display values between 0.01 and 100 MPa. The results indicate the route for the development of polymers with a very broad range of properties similar to those of natural cartilage tissue. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3682–3688, 2013     

Performance prediction of weldline structure in amorphous polymers

The presence of a weldline generally reduces the mechanical strength of injection molded parts. A typical remedy to eliminate the problem of weak weldline structure has been to increase the melt temperature. This, however, is not an acceptable solution in some situations. A general solution to the weak weldline problem requires an in-depth understanding of the thermomechanical history of the injection molding process. A theoretical model for the strength of weldlines is presented that provides a comprehensive physical insight of the bonding process at the weldline interface. The model is based on the self-diffusion of molecular chains across the polymer-polymer interface and the frozen-in orientation that remains parallel to the interface. Both factors are analyzed separately and then superimposed to predict the strength of weldlines from known processing conditions and geometry. Experimental results show good correlation with predictions.     

Effect of cryo-ground rubber on melt flow and mechanical properties of polypropylene

The influence of cryo-ground rubber (CGR) on melt flow and mechanical properties of polypropylene has been investigated. Cryo-ground rubber was incorporated in the polypropylene matrix (a) in powder form and (b) as masterbatch with natural rubber. Natural rubber was found essential as a dispersing agent. The loading of cryo-ground rubber has no significant effect on viscosity at high shear rates (>61 s^?1) but at lower shear rates (>61 s^?1), viscosity functions change shape with increasing cryo-ground rubber content. The dynamic mechanical properties revealed that polypropylene is thermodynamically incompatible with natural rubber and cryo-ground rubber. Cryo-ground rubber in the powder form shows poor adhesion to polypropylene matrix and, therefore, decreases the impact strength at higher loading. Addition of masterbatch of cryo-ground rubber and natural rubber improves the impact strength of polypropylene.     

Measurement and modeling of flow and mechanical properties of ASR-filled polymer composites

Screw extrusion process was used to evaluate the flow properties of ASR/LDPE composite whose rheological properties cannot be obtained from the conventional capillary rheometer measurements. The results show that the viscosity of the mixture increases with increasing automobile shredder residue (ASR) content. Although there exists significant scatter in the results because of the non-homogeneity of the mixtures, the result can be used to roughly predict the flow properties of the materials. Thus, based on linear regression fits of the flow data, a second order polynomial relationship was established between the viscosity of ASR/LDPE composite and ASR concentration. HDPE was used in the mechanical tests. The results also show that the tensile modulus can be predicted, accurately, using a conventional composite model.     

Evaluation of surface-active agents by mechanical properties of highly filled composites

Mechanical spectroscopy is used to study the behavior under accelerated aging of surface-active additives in highly filled composites using a binder based on an hydroxyl-terminated polybutadiene. First, the mechanical properties of composites containing an amine polyester or an aziridine polyester are compared to those of a composite without any surface-active agents. It is thus confirmed that the aziridine polyester is a better surface-active agent than the amine polyester. The improvement in properties from the aziridine polyester is not affected by accelerated aging at 333°K. It was also established that composites with a mixture of both polyesters showed adequate initial mechanical properties and maintained those properties upon accelerated aging. Various hypotheses are proposed to explain the behavior of surface-active agents.     

Evaluation of mechanical properties of epoxy–guar gum composites

Guar gum (GG) and hydroxypropyl guar gum (HPG) are widely used in a variety of applications ranging from foods, pharmaceutics to mining and explosives. However, there have been very few studies conducted investigating the use of these materials as fillers in polymer composites. GG and HPG were incorporated in an epoxy matrix and the mechanical properties of the resultant composites were determined. The tensile strength, flexural strength, and impact strength of the composites indicate that they provide reinforcement to the composites upto 5–7.5 phr after which there is a rapid decrease in the respective properties. HPG with higher propoxy content was found to provide greater reinforcement due to its increased hydrophobic nature leading to greater polymer–filler interaction. The nature of the filler required that the water absorption and related tests be carried out. The composites showed increased water absorption and also weight loss on exposure to acid and alkali environments, with HPGs showing greater variations when compared with GG, making the composites susceptible to moisture. The study shows that these fillers make an inexpensive, eco‐friendly, and renewable addition to conventional organic and inorganic fillers where the composites do not come into immediate contact with water. POLYM. ENG. SCI., 48:124–132, 2008. © 2007 Society of Plastics Engineers     

Melt flow properties,mechanical properties,thermal properties and morphology of polycarbonate/highly branched polystyrene blends

A highly branched polystyrene (HBPS) was synthesized via the copolymerization of 4‐(chloromethyl) styrene with styrene using the self‐condensing atom transfer radical polymerization method. The addition of HBPS as a melt modifier for polycarbonate (PC) was attempted. Melt flow properties, mechanical properties, thermal properties and morphology of the blends were studied. The results showed that a significant drop in the blend viscosity occurs immediately on addition of HBPS. Impact strength, tensile strength and glass transition temperature (T_g) of all the blends have not been significantly reduced compared with those of pure PC. The TGA analyses showed that an initial weight loss temperature of all the blends is above 458 °C and slightly low compared with that of pure PC, but all the blends still have excellent thermal stability. Morphological studies using SEM showed that a two‐phase morphology is characteristic of all the blends, with more or less spherical droplets of the minor HBPS phase dispersed in the continuous PC phase. Copyright © 2006 Society of Chemical Industry     

Evaluation of flow properties of toner powder using conical rotor

In order to accurately evaluate the dynamic flow properties of toner powder, a new rotary shearing tester with a conical rotor was developed. This instrument was equipped with an automatic pressing system to compress toner powder. The tester could simultaneously measure torque and compression load during the intrusion and rotation of the conical rotor into the same packed toner powder. The optimum rotational speed and intrusion rate of the conical rotor for the characterization of the flow properties of toner powder were discussed based on test results; their values were calculated as 0.017 s^− 1 and 0.083 mm/s, respectively. The torque of toner powder changed in proportion to the cube of the depth of intrusion in the toner powder bed. The surfaces of toner powder samples prepared from polymer resin and carbon pigment particles were coated with fine particles (SiO₂, TiO₂) under a different condition. The flow characteristics of toner powder with a different particle surface were evaluated based on the relationship between the shearing torque and the void fraction of packed toner. In the present case, the Rumpf model was applied to estimate the shearing force H at the contact point between two particles of toner powder. The value of H for toner powder with a rough particle surface, which was covered with fine particles (SiO₂, TiO₂), was 41 nN, while that for toner powder with a smooth particle surface, which was not covered with fine particles, was 357 nN. Further the effects of the particle shape of the toner on the torque of toner powder after compression under the same conditions were investigated. The torque of toner powder decreased with an increase in circularity.     

A study of the flow properties of rubbers using the rheometrics mechanical spectrometer

The dynamic shear properties of a natural rubber and several commercial synthetic polyisoprenes were measured in a Rheometrics mechanical spectrometer. The dynamic viscosity vs angular velocity curve was fitted to the three-constant Car, reau model. The rheological parameters were correlated with molecular characteristics such as gel content and weight average molecular weight. The viscosity measurements at high shear rate were obtained from capillary rheometry. The viscosity vs shear rate curve at the low shear rate end was found to be superimposible on the plot of dynamic shear viscosity vs twice the angular velocity.     

Evaluation of mechanical properties and hydrophobicity of room-temperature,moisture-curable polysilazane coatings

Polysilazane coatings have a broad need in real-life applications, which require low processing or working temperature. In this work, five commercially available polysilazanes have been spin-coated on polycarbonate substrates and cured in ambient environment and temperature to obtain transparent, crack-free, and dense films. The degree of crosslinking is found to have a significant impact on the hardness and Young's modulus of the polysilazane films but has a minor influence on the film thickness and hydrophobicity. Among all five polysilazane coatings, the inorganic perhydropolysilazane-based coating exhibits the largest hardness (2.05 ± 0.01 GPa) and Young's modulus (10.76 ± 0.03 GPa) after 7 days of curing, while the polyorganosilazane-derived films exhibit higher hydrophobicity. The molecular structure of polysilazanes plays a key role in mechanical properties and hydrophobicity of the associated films, as well as the adhesion of coatings to substrates, providing an intuitive and reliable way for selecting a suitable polysilazane coating material for a specific application.     

Preparation of SBA-15 extrudates: Evaluation of textural and mechanical properties

SBA-15 powder (P) was shaped into cylindrical extrudates (Ex) by compounding with additives such as bentonite (binder), methylcellulose and tetraethylorthosilicate (TEOS). The extrudates of SBA-15 were characterized by XRD, N₂ adsorption and thermogravimetric analysis. The orderly growth of SBA-15 is evident from the XRD patterns. The surface area and pore volume of SBA-15 (P) were around 884 m²/g and 1.1 cm³/g, respectively. The decrease in surface area and pore volume were observed for SBA-15 (Ex) in comparison to SBA-15 (P). This may be due to partial blocking of pore entry and surface coverage of additives during shaping of extrudates. The mechanical strength of SBA-15 (Ex) was examined by vertical crushing method. The effect of additives on the mechanical strength of SBA-15 (Ex) was examined by varying the composition. The results indicate linear increase of mechanical strength with increase in the content of bentonite and methylcellulose, but non-linear response with increase of TEOS and water. Compounding additives have been established to improve the mechanical strength of the extrudates.     

注射成型熔接线区域流动诱导双折射行为

带有熔接线的透明聚苯乙烯平板制品通过带嵌件的模具注射成型,利用光弹测试考察了不同工艺条件下的制品双折射行为,探讨了嵌件造成的相邻熔接线区域熔体流动行为及对制品双折射分布的影响。结果表明,保压压力和熔体温度对制品双折射整体分布影响明显;嵌件后熔接缝区域与制品其他区域的双折射行为有较大差异,其变化与熔体相遇后流动行为和熔接部位分子取向分布有关;制品最大双折射值出现在嵌件后一定距离处。热收缩实验进一步验证了上述结果。     

SBS／ESBS共混体系力学性能及熔体流动速率的研究

研究了苯乙烯-丁二烯-苯乙烯（SBS）和环氧化苯乙烯-丁二烯-苯乙烯（ESBS）质量配比及ESBS环氧基质量分数对SBS／ESBS共混物的力学性能以及熔体流动速率的影响。结果表明,随着SBS与ESBS质量配比的减小,共混物的绍尔A硬度逐渐增大,拉伸强度和断裂伸长率先增大后减小,熔体流动速率先减小后增大。当SBS和ESBS质量配比为60：40时,共混物的邵尔A硬度为85,拉伸强度和断裂伸长率分别为26．86MPa和795．5％,综合性能最佳。随着ESBS环氧基质量分数的增大,SBS／ESBS共混物的硬度逐渐增大,拉伸强度和断裂伸长率降低,熔体流动速率变小。     

Evaluation of structural and mechanical properties of aerosol-deposited bioceramic films for orthodontic brackets

Four types of bioceramic films (Al₂O₃, SiO₂, hydroxyapatite (HA), and brushite) were prepared via a simple aerosol deposition (AD) process at room temperature, and their structural and mechanical characteristics were compared to verify their potential for use in orthodontic brackets. The results showed that the HA and brushite films featured considerably high deposition rates compared with other coating technologies. Moreover, it was revealed that the crystallite size of all samples was largely reduced below 100?nm, which can enhance the biological performance and mechanical properties of bioceramic films. The HA and brushite films also had optimum mechanical properties, namely, adhesive strength and shear bond strength. These two instrumental mechanical properties were believed to be achieved by not only thicker bumps due to the high deposition rate but also strong mechanical interlocking at the ceramic-to-resin interface. This study confirmed that AD-prepared HA and brushite films have high potential for application in orthodontic brackets.     

Evaluation of dynamic mechanical properties of unidirectional composites in relation to their morphology

We were interested in the dynamic mechanical behavior of unidirectional composites from E-glass fibers and an epoxy matrix with several glass fiber contents ranging from 43% to 68%. A method is proposed for the determination of the viscoelastic response of such reinforced material, based on successive applications of the three-phase self-consistent analysis proposed by Christensen and Lo. When we apply this model in consecutive steps, we can take into account some morphological features including nonuniform arrangement of the fibers in the transverse plane with clustering or connecting arrangements as well as particular strengthening effects of the polymer in the interphase.     

Variation of flow induced phase morphology of fluoroelastomer and polycarbonate blends and their mechanical properties

The variations of the flow induced phase morphology of fluoroelastomer/polycarbonate (FL/PC) extruded blends and their mechanical properties were investigated in this paper. The phase morphology and mechanical property of extruded blends under the capillary die were examined by scanning electron microscope (SEM) and tensile machine, respectively. From SEM observation, the dispersed phases in the longitudinal direction for these extruded blends were categorized as sphere, ellipsoid, rod, and fiber. Furthermore, the processing window for the deformation of phase morphology in the longitudinal direction for FL/PC 10/90 w/w and 25/75 w/w extruded blends at 235 and 260 °C was studied. As shear stress was smaller than 7.0 × 10⁴ Pa, the spherical phase almost did not deform. The transformation from the sphere to the fiber form occurred in the range of shear stress 7.0 × 10⁴ Pa and 15.8 × 104 Pa. In particular, as shear stress was larger than 15.8 × 10⁴ Pa, the fiber broke up into a series of small droplets. Finally, it was concluded that the morphology with the mixture of fiber-like and spherical structures in the longitudinal direction could enhance the FL/PC blends with longer break elongation and higher Young’s modulus.