Shear and extensional properties of short glass fiber reinforced polypropylene

Shear and extensional properties of a commercial short glass fiber reinforced polypropylene were carefully investigated using commercial rheometers and a novel on‐line rheometer. This on‐line slit rheometer, installed on an injection molding press, has been designed to measure the steady shear viscosity, the first normal stress difference, and the apparent extensional viscosity of polymer melts and composites for high strain rates up to 10⁵ s⁻¹ in shear and 200 s⁻¹ in extension. Our results show that the steady‐state viscosity measurements using the on‐line rheometer are in excellent agreement with those obtained using commercial rheometers. The steady‐state and the complex viscosities of the composites were found to be fairly close to that of the matrix, but the Cox‐Merz rule was not verified for the composites at high rates. The elasticity of the composites was found to be equal to that of the polypropylene matrix. The apparent extensional viscosity was obtained from the pressure drop in the planar converging die of the slit rheometer using the analyses proposed by Cogswell [1] and Binding [2]. The extensional viscosity of the polypropylene was found to be much larger than the shear viscosity at low strain rates with a Trouton ratio of about 40 that decreased rapidly with increasing strain rate down to the value of 4 at 200 s⁻¹. The extensional viscosity of the composites was also found to be close to that of the matrix, with values 35 and 5% larger for the 30 and 10 wt% reinforced polypropylenes, respectively. These results are compared with the predictions of the Goddard model [3], which are shown to overpredict our experimental results. POLYM. COMPOS. 26:247–264, 2005. © 2005 Society of Plastics Engineers.     

Interfacial crosslinking and diffusion via extensional rheometry

When a coextruded multilayer sheet is pulled in a uniaxial extensional rheometer the interfacial area per unit volume increases, amplifying interfacial effects. To investigate interfacial reaction, a pair of functional and miscible polyethylenes were co‐extruded into multilayer sheets (256 layers). One polyethylene contained 8 wt% glycidyl methacrylate comonomer the other 4 wt% anhydride grafts. The extensional force to pull the molten multilayer sheet was measured via a rotating clamp extensional rheometer (RME, Rheometric Scientific). Owing to the reaction in the interfacial region before and during the extension, the measured extensional force increased dramatically. The interfacial stress was extracted and correlated to the extent of interfacial crosslinking. The rate of interfacial crosslinking was found to exceed the rate of area generation at extension rates < 0.01 s^?1. By annealing samples and then stretching them, the growth rate of the interlayer was determined, and a diffusion coefficient estimated.     

Preparation and characterization of graphene reinforced PA6 fiber

Here, we report the successful preparation of PA6/GO composite fibers through in situ polymerization and the melting spinning method. The results suggest that graphene has induced only minor changes on the relative viscosity yet exhibits significant effects on the crystallization characteristics. The SEM images of the fibers have shown several expended borders as a consequence of graphene addition. The maximum strength of the composite fibers (5.3 cN/dtex) has been reached 0.05 wt % graphene added to the system; the draw ratio was equaled to 3.8. Compared to the neat PA6 fiber, the fibers with graphene displayed superior creep resistance features; the creep rate constant was 0.38 at a 0.05 graphene concentration, with a draw ratio of 3.5. The approach employed in this research paves the way towards PA6/graphene nanocomposites have been prepared through in situ polymerization using caprolactam and graphene oxide/water pulp as starting materials. In situ polymerization approach facilitated a superior interaction between PA6 and graphene. Compared to graphene oxide powder, the graphene oxide in water pulp has prevented the agglomeration when added to the caprolactam melt, leading to its enhanced dispersion within the system. PA6/graphene as‐spun fiber has been produced by the mean of melt‐spinning strategy using a melt‐spinning machine, obtaining products with different draw ratios after drawing at 120 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45834.     

Fabrication and characterization of hollow nanofibrous PA6 yarn reinforced with CNTs

Core-sheath nanofibrous yarns were obtained through electrospinning of polyamide 6 (PA6) solution containing different concentrations of multi-wall carbon nanotubes (MWNTs) as sheath and PVA multifilament as the yarn core. By dissolving PVA, for obtaining conductive hollow nanofibrous PA6/MWNTs yarn, two types of porosity could be obtained including hollow central tube due to the structure of hollow yarn and nano-porous areas embedded in electrospun nanofibers. SEM results showed that the diameters of nanofibers were varying in the range of 103–145 nm obeying MWNTs concentrations and TEM results revealed that the MWNTs were embedded in nanofiber matrix as straight and aligned form. DSC analysis showed that electrospinning process caused the formation of less-ordered γ phase in nanofibers. The electrical conductivity of yarns increased from 10^?13 S m^?1 to 2.4?×?10^?6 S m^?1 with increasing the concentration of nanotubes from 0 wt.% to 7 wt.%.     

The use of extensional rheometry to establish operating parameters for stretching processes

This work describes a method of determining the limits of uniform extensibility, in terms of failure and fracture, from rheological tests in extensional flow. The limit of uniform stretching can be expressed in terms of the Weissenberg number for the process, as demonstrated by data for three chemically diverse polymers, polystyrene, poly(methyl methacrylate), and a polyester. The BKZ-K model can be used to predict necking failure, as determined by the Considére criterion, and an empirical correlation can be derived for fracture.     

Shear viscosity of nylon 6 melts reinforced with microfibrous calcium silicate hydrate

Steady shear viscosity of nylon 6 melts reinforced with xonotlite, microfibrous calcium silicate hydrate (6CaO · 6SiO₂ · H₂O), is investigated. The highly filled nylon 6 melt tends to exhibit a yield value, resulting in remarkable viscosity increase particularly at low shear rates. Addition of the xonotlite significantly increases activation energy of viscous flow of the nylon 6 melt, leading the viscosity to be strongly temperature dependent. Comparisons with the melts filled with glass fibers and wollastonite are made. Flow-induced orientation becomes more important at low volume fractions. Shortening of the xonotlite during shear flow measurement can also be observed.     

Fibre reinforced nanocomposites: Mechanical properties of PA6/clay and glass fibre/PA6/clay nanocomposites

In this paper, the effect of two different reinforcements: clay at the nanoscale and glass fibres at the micro-scale, on the mechanical properties of PA/clay and GF/PA/clay are studied. The Halpin-Tsai model is used to predict the modulus of PA/Clay and GF/PA/Clay, both of which are influenced by two factors: reinforcement shape and volume fraction. The relationships between the modulus and reinforcement shape and volume fraction are discussed. Tensile modulus, measured in tensile tests is used to fit the Halpin-Tsai models. The results demonstrate a synergy between the reinforcements at the two different scales.     

Capillary breakup extensional rheometry of associative and hydrolyzed polyacrylamide polymers for oil recovery applications

High molecular weight polymers used for heavy oil recovery exhibit viscoelasticity that can influence the oil recovery during chemical enhanced oil recovery. Different polymers having similar molecular weight and shear rheology may have different elongation flow behavior depending on their extensional properties. Displacing slugs are more likely to stretch than shear in tortuous porous media. Therefore, it is critical to seek an analytical tool that can characterize extensional parameters to improve polymer selection criteria. This article focuses on the extensional characterization of two polymers (hydrolyzed polyacrylamide and associative polymer) having identical shear behavior using capillary breakup extensional rheometer to explain their different porous media behavior. Maximum extensional viscosity at the critical Deborah number and Deborah number in porous media classified the associative polymer as the one having high elastic‐limit. Extensional characterization results were complemented by significantly higher pressure drop, marginally increased oil recovery of associative polymer in porous media. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46253.     

碳纤维增强PPO/PA6共混物的研究

通过熔融挤出制备聚苯醚接枝马来酸酐（PPO-g-MAH）作为聚苯醚/尼龙6（PPO/PA6）共混物的相容剂,再与苯乙烯-乙烯-丁二烯-苯乙烯嵌段共聚物（SEBS）、碳纤维（CF）共混制备PPO/PA6/PPO-g-MAH/SEBS/CF复合材料。CF经侧喂料口加入,通过改变螺杆转速来制备不同CF含量的复合材料。通过动态热机械分析（DMA）、毛细管流变和力学性能测试等方法研究了CF含量变化对复合材料热机械性能、流变行为、力学性能等的影响。再与相同条件下制备的玻璃纤维（GF）复合材料进行比较,通过扫描电子显微镜观察（SEM）和力学性能测试,表明CF能够更好的被基体树脂包覆,制得的复合材料性能更优。     

Shear and extensional flow of reinforced plastics in injection molding. I. Effects of temperature and shear rate with bulk molding compound

Capillary flow studies on bulk molding compound (BMC) using an instrumented injection-molding machine are reported. The significance of extensional flow effects with fiber-reinforced materials is emphasized. The extensional flow behavior in converging dies is modeled, and a means of evaluating both extensional and shear viscosity from capillary flow data is proposed. Methods of correcting results for the effect of deformation heating are discussed. The shear and extensional flow behavior of BMC in the temperature region 18 to 58°C can be fitted to a simplified Arrhenius Law.     

Shear and extensional viscosity of thermally aggregated thermoplastic protein

Novatein is a thermoplastic produced from blood meal and is used in different agricultural applications. Novatein has some unique processing challenges and its rheology was studied using screw-driven capillary rheometry, with a particular focus on sheet extrusion using ethylene glycol, glycerol, propylene glycol (PG), or triethylene glycol (TEG) as plasticizers. The entrance pressure drop contributed up to 44% of the total pressure drop (entrance and capillary pressure drop), but this was significantly reduced by plasticization or increased temperature. Polyol addition led to higher shear viscosities in comparison to no polyol plasticization, most likely due to improved chain mobility resulting in orientation effects. Elongational flow was dominated by primary plasticization of the protein-rich phase and changes in secondary structure, whereas secondary plasticization (phase separation into a polyol-rich phase) played a significant role in the reduction of the shear viscosity. Of the selected plasticizers, PG showed the most efficient plasticization in both shear and elongational flow. When combined with the beneficial secondary structural changes brought about by TEG, the sheet forming ability of Novatein was drastically improved.     

玻璃纤维增强PA 6/PBT低吸湿共混物的力学性能

以马来酸酐接枝乙烯-辛烯共聚物(POE-g-MAH)和乙烯-甲基丙烯酸丁酯-丙烯酸缩水甘油酯三元共聚物(PTW)为复合相容剂,在平行同向双螺杆挤出机上熔融共混,制备了玻璃纤维增强聚酰胺(PA)6/聚对苯二甲酸丁二酯(PBT)共混物。考察了复合相容剂对增强共混材料力学性能的影响,并探讨了共混物的吸湿性与力学性能的关系。结果表明:相容剂的复合使用有协同作用;PA 6/PBT共混体系随w(PBT)增加,力学性能下降,w(PBT)增加到32.0%时,拉伸强度、弯曲强度、简支梁缺口冲击强度分别下降25.2%,15.8%,45.3%;并且随w(PBT)增加,共混体系对吸湿的敏感性降低。     

碳纳米管增强PA6纤维纺丝工艺的研究

将含有碳纳米管(CNTs)的母粒与PA6切片及稳定剂熔融共混纺丝,可制得增强的PA6/CNTs纤维。探讨了纺丝温度、初生纤维的放置时间、热定型时间等对PA6/CNTs纤维强度的影响。结果表明,CNTs 质量分数为0.03%,纺丝温度为288℃,热定型时间为10 s,放置时间为4 d时,纤维增强效果最佳。     

短玻璃纤维增强低熔点尼龙6复合材料的性能研究

研究了短玻璃纤维用量对低熔点尼龙6(LMPA6)复合材料力学性能和热性能的影响。结果表明:随着短玻璃纤维用量的增加,LMPA6的缺口冲击强度先增加后降低,最高值为6.46KJ/m2;拉伸强度和弯曲强度则随之提高,当短玻璃纤维的用量为30%时,拉伸强度提高到100MPa,弯曲强度提高到130MPa以上。LMPA6的维卡软化点也随短玻璃纤维用量的增加而提高,当短玻璃纤维的用量为30%时,维卡软化点提高到90℃。     

热氧老化对长玻璃纤维增强聚酰胺6复合材料的影响

研究了160℃条件下不同热氧老化时间对未添加抗氧剂和添加抗氧剂的长玻璃纤维(LGF)增强聚酰胺(PA)6(PA 6/LGF)复合材料力学性能、热稳定性、结晶度及表面形貌的影响,并采用热重分析,差示扫描量热法分析和扫描电子显微镜观察对PA 6/LGF复合材料进行了表征。结果表明:PA 6基体分子链的断裂、降解以及LGF与PA 6基体的脱黏导致了PA 6/LGF复合材料宏观力学性能、熔融温度、结晶温度、结晶度以及热稳定性的下降。添加抗氧剂的PA 6/LGF复合材料拉伸强度保持率为83.9%,而未添加抗氧剂的复合材料则为76.8%。添加抗氧剂能使PA 6/LGF复合材料具有相对优异的力学性能保持率。     

高灼热丝引燃温度高漏电起痕指数的阻燃PA6/GF

采用双螺杆挤出机制备了阻燃玻璃纤维(GF)增强聚酰胺(PA)6(PA 6/GF)复合材料,研究了阻燃PA 6/GF复合材料的灼热丝引燃温度、漏电起痕指数、阻燃性能和力学性能。研究表明:当PA 6为32.0 phr,磷-氮系阻燃剂为20.0 phr,溴化聚苯乙烯为10.6 phr,复合锑为3.4 phr,GF为23.0 phr,BaSO4为7.0 phr,增韧剂为3.0 phr时,阻燃PA 6/GF复合材料(2.0 mm厚)的灼热丝引燃温度可达850℃、漏电起痕指数达425 V,复合材料(1.6 mm厚)的阻燃性能达UL94 V-0级,并且具有较好的力学性能。     

Polycarbonate reinforced with silica nanoparticles

Nanocomposites of polycarbonate (PC) reinforced with nanosized silica particles were prepared by a melt mixing technique in an internal mixer. Two kinds of commercial hydrophilic fumed silicas differing in their specific surface area were added in amounts up to 5% by volume, and their reinforcing action was compared to that of organically modified silica, loaded in the same amounts. Particle–matrix interactions were investigated by means of rheological and dynamic-mechanical thermal analysis, demonstrating the important role played by the organic modification in the interactions with the polymer matrix, and showing an optimal nanoparticle loading around 2 vol%. The scratch resistance of the nanocomposites obtained from hydrophilic silicas was investigated, and a remarkable enhancement in the indenter’s penetration resistance was observed for all the compositions with respect to pristine PC. The same behaviour was observed for the Shore D hardness and for the impact resistance of the nanocomposites that also significantly improved with the maximum load shifting from a minimum value of 521 N for pristine PC up to values grater than 1330 N for the nanocomposites, demonstrating the activation of effective mechanisms of energy dissipation due to the presence of the nanofillers.     

Shear and extensional flow of a thermotropic liquid crystalline polymer

The flow of a thermotropic liquid crystalline polymer (unfilled and glass fiber filled) was studied using a capillary rheometer and an instrumented injection molding machine. Despite different thermal histories, the techniques gave similar results. From 330 to 350°C, viscosity was independent of temperature. At 340°C, where most measurements were carried out, pronounced shear-thinning occurred and the shear flow curves were nonlinear, the power law exponent decreasing from 0.51 at a shear rate of 10 s⁻¹ to 0.35 at 10⁴ s⁻¹. A previously reported model was used to derive elongational flow curves from die entry pressure data. Because of the nonlinearity of the flow curves, quadratic log-stress vs. log-strain rate plots were needed to model behavior over the strain rate region studied. The elongational flow curves were similar in shape to the shear flow curves, with an effective Trouton ratio of 30. Despite orientation and structure present in the melt, the extensional viscosities and Trouton ratios were within the range found with normal thermoplastic melts. The results suggest that extensional flow may be inhomogeneous, the flowing units possibly being partially ordered domains.     

Exfoliated PA6,6 nanocomposites by modification with PA6

Minor amounts of a fully exfoliated PA6/commercial OMMT nanocomposite were used as a master-batch to produce exfoliated PA6,6 based nanocomposites. The major component PA6,6, which was fully mixed with PA6, did not largely affect the interactions between the OMMT and the surrounding polymer, as the exfoliation level of OMMT increased upon blending with PA6,6. Both the phase behaviour and the mechanical properties of the nanocomposites were compared with those of the PA6,6-rich matrix, to assess the separate effects of the PA6 and the OMMT. The large exfoliation level attained, led to increases in the modulus of elasticity that reached 46% with 5 wt% OMMT, and to the presence of highly ductile materials up to 3 wt% OMMT content.