Effect of annular expansion pipe extruder head on mechanical properties of pipes

With polymer pipes being used more commonly, performance requirements are increasing. Studies on the enhancement of mechanical properties of polymer pipes are particularly important. In this study, a self-designed annular expansion pipe extruder head was used to enhance the mechanical properties of HDPE pipes. Different morphologies of the HDPE pipes were produced under different processing conditions. When the extrusion angle was 30° (P30), the best mechanical properties were obtained. The hoop tensile strength and axial tensile strength were 14.5% and 41.0% higher, respectively, compared with the specimen without expansion (P0). This improvement of mechanical properties can be attributed to several reasons. First, the processing parameters of P30 reached the threshold shear rate and strain for shish-kebab formation, as shown by scanning electron microscopy. Second, P30 has the highest orientation parameter and crystallinity of 0.679 and 67.27%, respectively, from 2D wide-angle diffraction (WAXD). Polarized FTIR shows the same trend as 2D-WAXD. Third, the outer bamboo-like self-reinforced structure is formed inside the pipe at 30° expansion angle while the core layer has a well-formed crystal structure; the special structure improves the overall performance of HDPE pipe. This method can be utilized in large-scale industrial production.     

Analysis and calculation of the electric drive for the extruder in a controllable electrical complex for production of synthetic yarns

The conditions that function W_e(z), which ensures the minimum acceptable time of the switching process, must satisfy can be formulated as follows: — function W_e(z) should have nulls equal to the poles of W_n(z) positioned in the unit circle or outside of plane z; — function W(z) or 1 — W_e(z) should have all nulls of W_n(z) located in the unit circle or outside of plane z as nulls; — function W(z) or 1 — W_e(z) should contain z⁻¹ as cofactor z⁻¹. If W_n(z) is an unstable unit impulse response, then F(z) should contain all poles of W_n(z) lying in the unit circle or outside of plane z as nulls (with the exception of the poles for z = 1). If W_n(z) has nulls located in or outside of the unit circle, these nulls must be nulls of W(z) = 1 − (1 − z⁻¹). In these two cases, the briefest time of the switching process will exceed the value which can be obtained for a system with a stable unit impulse response W_n(z) which has no nulls in or outside of the unit circle of plane z. __________ Translated from Khimicheskie Volokna, No. 56–59, March–April, 2008.     

Effect of cure history on dynamic mechanical properties of an epoxy resin

The effect of cure history on the dynamic thermomechanical properties of a high temperature curing epoxy resin has been studied using torsional braid analysis. In isothermal cures “full cure” is not possible except at temperatures above the maximum glass transition temperature (T_g) of the cured resin, hence the necessity of a “post-cure” after lower temperature isothermal cures. The highest T_g and maximum cross-linking in the cured resin was for a linear heating rate of 0.05°C/min from 30 to 200°C; higher heating rates lead to lower glass transition temperatures.     

Effect of extruder elements on fiber dimensions and mechanical properties of bast natural fiber polypropylene composites

Illusions and facts about aspect ratio and the corresponding mechanical properties of the polypropylene flax are studied in this work. Selection of extruder elements controls significantly the fiber final dimensions. Hence, the load transfer efficiency can be improved. Different extruder layouts are tried. First and second trials investigate the mixing degree effect using kneading elements with eight and four kneading elements, respectively. The third and fourth trials keep four kneading blocks but differentiate in using multiprocessing element MPE and toothed elements, respectively. All the four configurations are tested at different shearing rates namely 100, 200, and 300 rpm and different fiber loadings 10, 20, and 30 wt %. Polypropylene (PP) with high flowing properties and slivers flax natural fibers are used. The output extruded strands are mechanically tested. The third and fourth configurations showed superiority to the normal kneading profiles regarding the mechanical properties. Samples of composites are withdrawn after each processing extruder element to study the effect of this element on the fiber dimension. Measurement of extracted fibers is carried out by two methods namely dynamic image analysis machine and secondly normal microscopic investigation. Weibull distributions are defined for fiber geometry distributions for the different locations on the extruder configuration. Also, the effect of the shear rate and the extruder configuration on the final dimensions of the fibers extracted from the composite. The results show the correlation between extruder configuration and fiber aspect ratio and hence the composite overall strength. However, further processing like injection molding erases the pre‐extrusion effect. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40435.     

Effect of the thermal history of polymers on their dynamic mechanical properties

A torsion pendulum was used to compare quenched and annealed specimens of representative polymers with respect to their dynamic mechanical properties. Among amorphous polymers, the effects of thermal history appear to be both moderate and similar for different polymers. For some crystalline polymers, the effects of thermal history are again moderate. However, the effects are very great in one of the crystalline polymers selected, presumably because it is easily supercooled below its melting point.     

Effect of photodegradation on dynamic mechanical properties of nylon 6

Changes in the dynamic mechanical properties of nylon 6 (α-form) under ultraviolet light irradiation were investigated. On irradiation with spectrally dispersed ultraviolet light in the wavelength range of 219–415nm, the dynamic modulus E′ and the density of nylon 6 were increased below about 300nm. It was found that the increment in E′ and the density were the result of crosslinking. When E′ was measured with time elapsed during irradiation by light of 253.7 nm, E′ initially decreased with time, increased at a longer time, and then reached a limiting value asymptotically. From the result of the change in E′ with time, it was assumed that the scission and crosslinking reactions occur simultaneously during ultraviolet light irradiation. Thus, the change in E′ with elapsed time was exppressed by the equation E′_t = E′₀ exp (?k₁t) + E′_∞[1 ? exp (?k₂t)], where E′_t is the dynamic modulus at time t, E′₀ is the E′ at t = ₀, E′_∞ is the limiting value of E′, and k₁ and k₂ are the rate constants. The apparent activation energies for k₁ and k₂ were 3.23 and 2.50 kcal/mole, respectively, and the former value agreed with the activation energy for the scission of the amide groups. The effects of the photodegradation on the temperature dispersion of nylon 6 were also investigated. On irradiation with light at 253.7 nm, the α-relaxation which appeared at about 90°C was broadened and the intensity of the γ-relaxation at ?95°C in the tan δ-versus-temperature curve was lowered. The β-relaxation which appeared at ?45°C for the wet nylon 6 decreased its intensity.     

退火对聚碳酸酯注塑制品力学及动态力学性能的影响

本文研究了聚碳酸酯（Lexan OQ2720）注塑制品退火后的力学及动态力学性能的变化。结果表明,制品的应力集中情况有明显改善,力学性能除断裂伸长率外都产生了较高提升,拉伸强度提高了14.86%,弯曲强度提高了12.7%,弯曲模量提高了21.27%,冲击强度提高了17.93%;动态力学分析结果表明,,注塑制品的内部存在应力。经退火后,注塑制品内部取向、缠结的分子链得到充分松弛,制品储能模量随温度的变化呈线性规律,内部链段的状态稳定,热变形温度得到了提高。而未退火试样的储能模量随温度变化起伏不定,内部链段的状态比较活跃。动态频率对制品中应力有一定响应能力,响应频率范围约为30-60Hz,随着频率扫描温度的升高,由于应力集中降低,频率对应力响应能力不断降低。     

密炼机转子直径对降温性能的影响

要获得质量好的混炼胶抖,必须经过充分的混炼,选用适宜的混炼机是非常重要的,控制加工温度是胶料在混炼机内混炼的关键。特别是白炭黑胶料的混炼必须控制其温度,所以,对混炼机进行降温就显得尤为重要。文中将新型加压式55L捏和机与老式的75L密炼机进行了降温对比试验。测定了整机及各个部位的降温幅度和导热率。     

Blends of nylon with polyethylene: Effect of compatibilization on mechanical and dynamic mechanical properties

Blends of Nylon 6 with very low density polyethylene (VLDPE) have been studied. The blends exhibit two phase morphology wherein VLDPE is dispersed in the form of spherical domains in Nylon 6 matrix. The water absorption of the blends decreased with increasing VLDPE content. The mechanical properties of these blends show loss in tensile and impact strength due to poor adhesion at the interface. Addition of a compatibilizer containing MAH groups was found to result in improved properties. The tensile strength increased significantly whereas impact testing showed no break confirming better stress transfer across the interface. The dynamic mechanical analysis showed presence of microheterogeneity resulting into merging of tan delta peaks as a result of compatibilization. The observed results are ascribed to the possible reaction between reactive groups in Nylon 6 and the compatibilizer leading to compatibilization through copolymer formation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 161–168, 1998     

Effect of hygrothermal fatigue on dynamic mechanical properties of glass-reinforced polyesters

Several nonreinforced and reinforced crosslinked polyester formulations were prepared and investigated. Solid glass microspheres, with and without coupling agent, were used as reinforcement. All samples were exposed to various cyclic hygrothermal fatigue patterns, differing from one another by the temperature and duration of a cycle. Dynamic mechanical measurements were used to evaluate the effect of hygrothermal fatigue on the mechanical properties of all formulations. Fatigue induced changes in the glass–matrix interphase led to the appearance of relaxation peaks (β′ and β″) in the temperature range between ?50°C and ?10°C. Electron microscopic evidence was obtained for the existence of nodular morphology on all fracture surfaces. The character of nodular morphology was described in terms of an inhomogeneous thermoset network.     

The effect of axial pressure gradient on extruder mixing characteristics

Many twin screw extruders are operated in the starve-fed mode with the majority of the extruder having partially-filled channels. There will always be regions of totally filled channels due to the presence of the die or reverse elements. The authors experimentally show the effect of the change of percent drag flow on the rate of distributive mixing in the co-rotating and counter-rotating twin screw extruder. Optimum operating conditions for distributive mixing are identified experimentally and verified theoretically.     

Effect of the shaft eccentricity and rotational direction on the mixing characteristics in cylindrical tank reactors

Strategy of the shaft eccentricity is introduced to enhance the mixing characteristics in a flat bottomed cylindrical vessel without baffles. The mixing is ensured by a six-curved blade impel er. Three solutions which are models of food emulsions are used as working fluids. These solutions have a shear thinning behavior modeled by the power-law. The effects of fluid properties, stirring rates, impeller rotational direction and impeller eccentricity on the 3D flow fields and power consumption are investigated. Three values of impeller eccentricity are consid-ered, namely 0%, 24%and 48%of the vessel diameter. It is found that the opposite clockwise rotational direction reduces the power consumption, compared with the clockwise rotational direction. Also, the obtained results show that an impeller placed at an eccentric position between 24%and 48%of the vessel diameter and at the third of the vessel height may ensure the best mixing characteristics.     

同向旋转三螺杆挤出机固体输送段输送特性研究

基于离散元法分别对同向旋转的三螺杆以及双螺杆挤出机固体输送行为进行仿真模拟,对三螺杆挤出机颗粒速度分布以及受力分布进行分析,将三螺杆和双螺杆挤出机颗粒填充效率、输送质量以及质量流率进行对比分析.结果表明,位于螺棱和机筒附近位置的颗粒受到螺棱推力及机筒摩擦力影响较大,具有较高的速度;挤出机内部各区域颗粒填充顺序受螺杆旋转...     

注塑机肘杆合模机构弹性力学性能的探讨（三）

从注塑机肘杆合模机构弹性变形的运行特征进行分析研究,介绍了作者对弹性力学在注塑机肘杆合模机构中研究应用的一些成果。研究了拉杆和肘杆两者之间抗拉刚度的关系,提出了拉杆及肘杆根据拉伸刚度的设计方法及准则;研究了推力座导杆、销轴、模板支架、模板等抗弯挠度的特征及其相互之间的联系,提出了有关零件抗弯挠度的设计方法及准则;研究了有关零件的挠度和强度之间的内在联系,提出了根据挠度要求进行强度设计的准则。     

注塑机肘杆合模机构弹性力学性能的探讨（四）

从注塑机肘杆合模机构弹性变形的运行特征进行分析研究,介绍了作者对弹性力学在注塑机肘杆合模机构中研究应用的一些成果。研究了拉杆和肘杆两者之间抗拉刚度的关系,提出了拉杆及肘杆根据拉伸刚度的设计方法及准则;研究了推力座导杆、销轴、模板支架、模板等抗弯挠度的特征及其相互之间的联系,提出了有关零件抗弯挠度的设计方法及准则;研究了有关零件的挠度和强度之间的内在联系,提出了根据挠度要求进行强度设计的准则。     

Linear dynamic mechanical properties of an SBS block copolymer

Dynamic viscosity and elastic modulus for a low molecular weight styrene-butadiene-styrene (SBS) block copolymer ate measured as a function of temperature (80-170°C) and frequency using the eccentric rotating disc geometry. These linear properties are superimposed to yield master curves each of which exhibits two branches below different (critical) reduced frequencies. At lower temperatures, the non-Newtonian behavior characteristic of SBS block copolymers is observed. In contrast, Newtonian response occurs at higher temperatures. As a consequence, plots of the viscoelastic properties vs temperature exhibit discontinuities below the critical frequencies, reflecting a narrow transition at about 142°C. Above this temperature, it is inferred, consistent with the equality of dynamic and steady state viscosities, that the polystyrene (S) blocks, existent in dispersed domains at low temperatures, exceed a critical degree of compatibility with the continuous polybutadiene phase. The activation energies indicate that the S blocks affect the temperature dependence of the dynamic properties in proportion to their presence in an interphase which is assumed to continuously grow in size as temperature is raised to the transition temperature. Below the critical reduced frequencies, it is inferred that S domain disruption may increasingly occur in conjunction with the observed property enhancement due to these domains, relative to the miscible blocks, as reduced frequency is lowered. However, above these frequencies, the presence of frequency-temperature superposition implies that the S domains and the miscible blocks are equivalent in their effects on properties. At still higher reduced frequencies, the domains present at the low temperatures studied are assumed to remain intact, but plateau behavior similar to the response characteristic of homopolymers is observed.     

Effect of crystallinity on the dynamic mechanical relaxations of poly(butylene isophthalate)

Summary The viscoelastic spectrum of poly(butylene isophthalate) annealed at 90 °C for different times has been examined by dynamic mechanical spectroscopy.Crystallinity affects both the main a absorption associated with the glass to rubber transition and the sub-ambient secondary relaxation region. The latter results from two overlapping processes, ₁ and ₂, that have been evidentiated by a resolution procedure. Values of 52 and 76 kJ/mol have been obtained for the activation energies of the low (₁) and high (₂) temperature component respectively. It is suggested that these values are not affected by the methylene chain length and by the isomerism of the phthaloyl residue.