Rheological behavior of polymer melts with natural fibers

Flow behavior of polymer liquids filled with short fibers (particulate fillers) was theoretically analyzed from the point of view of the free volume theory. Assuming that the filler addition changes the occupied volume, while the temperature variations cause mainly the free volume changes, a general expression describing the viscosity of the system as a function of the filter content, temperature variations, and rheological properties of the pure polymer liquid was derived. If the viscosity curve of the unfilled polymer is described by the Carreau equation, the corresponding viscosity curve of the filled polymer is also represented by an equation of Carreau type. However, this equation has other values of Newtonian viscosity and the power exponent in comparison with the initial equation. Both parameters depend on the filler content and temperature. The derived equation predicts a viscosity rise and a stronger non‐Newtonian behavior of the system with increasing filler content. The temperature rise exerts an opposite effect on the rheological behavior. The theoretical predictions are in good accordance with viscosity measurements for low‐density polyethylene and polystyrene melts filled with short cotton, flax, and hemp fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1401–1409, 2005     

Effect of fillers on the rheological behavior of thermoplastic 1,2 polybutadiene rubber

The influence of fillers like clay, silica, and carbon black on the rheological properties of 1,2 polybutadiene has been studied using a capillary rheometer. Silica filled compound exhibited the highest viscosity and clay filled compound the lowest viscosity at all shear rates. The effect of filler loading and temperature on the Theological behavior has also been studied. Smooth extrudates were obtained in most of the cases and die swell was lower for silica and carbon black filled compounds than for clay filled compounds. Rheograms of different 1,2 polybutadiene systems have been found to merge into a master curve using modified viscosity and shear rate functions that contain melt flow index as a parameter.     

Fracture of particulate filled polymers

The addition of particulate mineral fillers to polymers confers certain mechanical property improvements automatically. Stiffness increases, creep diminishes and distortion at elevated temperatures is often reduced. However, the fracture energy of a polymer, as measured in impact, cracking or tearing tests, may vary quite unpredictably when filler is incorporated. In some special cases the fracture energy increases when small amounts of filler are added although it falls away again at higher volume loadings. This enhancement of polymer toughness by filler is an example of reinforcement. More generally the addition of filler causes a continuous and drastic reduction in fracture energy, resulting in a brittle, weak product. This paper seeks to explain the common degrading effect of filler on polymer fracture energy by considering the progress of a crack through the composite material. The crack travels through regions of polymer and also along the interfaces between polymer and filler. Experiment demonstrates that, although fracture of the polymer regions absorbs considerable energy, fracture of the interfaces usually requires very little. These weak interfaces do not resist cracking and are the cause of brittleness in particulate filled systems. This idea was quantified for thermoplastics such as low density polyethylene and poly (methylmethacrylate) filled with colloidal silica by twin-roll milling. Where the interfacial adhesive energy was much smaller than the polymer fracture energy, the composite toughness dropped as predicted when filler was added. The particle size, the nature or dispersion of the filler, and the crystallinity of the polymer used, had little influence on this phenomenon, as pointed out theoretically. The crucial parameters influencing the fracture energy of the filled polymer were found to be the volume fraction of filler and the interfacial adhesion between polymer and filler. By chemical treatments the adhesive energy between filler and polymer was raised until the interface was almost as tough as the polymer itself. In this case the filled polymer showed good fracture toughness, lending further support to the theory.     

Relative viscosity models and their application to capillary flow data of highly filled hard‐metal carbide powder compounds

The rheological behavior of highly filled polymer systems used in powder injection molding (PIM) technology strongly influences the final properties of the products. In this study, the capillary flow data of multi‐component polymer binders—based on polyethylene, paraffin, ethylene‐based copolymers, and polyethylene glycol—compounded with three various hard‐metal carbide powders were employed. The rheology of such highly filled (up to 50 vol%) multiphase systems is necessarily a complex phenomenon characterized by strain dependent, non‐Newtonian properties complicated by flow instabilities and yield. Over 15 mathematical models proposed for highly filled systems were tested, some of them calculating the maximum filler loading. Due to the complex structure of the filler (irregular shape, particle size distribution) and a multi‐component character of the binder, the applicability of these models varied with the powder‐binder systems studied. However, the particular values of maximum loadings are in good accordance with the predictions based on powder characteristics. Simple modification of Frankel‐Acrivos model to the systems containing unimodal hard‐metal carbide powders with particles of an irregular shape and broad particle size distribution gave precise agreement between experimental data and model prediction. POLYM. COMPOS., 26:29–36, 2005. © 2004 Society of Plastics Engineers.     

Application of two phase model to linear viscoelasticity of reinforced rubbers

A two phase model proposed for accounting for linear viscoelasticity of polymer nanocomposite melts [14] is applied to rubbers filled with nanoclay and conventional fillers (carbon black and silica) to probe mechanisms of the fluid- and the solid-like behaviors beyond the terminal flow region. This model shows strong applicability in linear rheology beyond terminal region for a variation of filled rubbers. Characteristic moduli of the “filler phase” from different filled rubbers could collapse onto a master curve, which reveals a jamming transition with increasing filler concentration across the percolation threshold. The strain amplification effect and reduced characteristic moduli of the “filler phase” are discussed within the framework of the cluster-cluster aggregation model.     

Effect of polymer matrix on the rheology of hydroxyapatite‐filled polyethylene composites

The effect of matrix polymer and filler content on the rheological behavior of hydroxyapatite‐filled injection molding grade high‐density polyethylene (HDPE) has been studied. Studies of the flow curves revealed that the matrix and the composite exhibit three distinct regions in the flow curve, namely, a pseudoplastic region at low to moderate shear rates, a plateau and a second pseudoplastic region at high shear rates. The shear stress corresponding to the plateau (τ_c) is dependent on both the filler concentration and the melt temperature. Addition of HA in the HDPE matrix increases the value of τ_c and decreases compressibility of the melt. An increase in temperature also raises the value of τ_c. From the nature of flow curves it is concluded that the matrix polymer largely decides the rheology of the composite.     

Rheological characterization of filled polyamide 11 and polyamide 12 solutions in polyols

A thorough understanding of the rheological properties of real-world, formulated polymer melts and solutions is important to fabricate articles via typical melt processing techniques. Polyamides have been studied extensively in the area of water purification applications. In this work, the viscosity of these homogeneous polyamide 11 and polyamide 12 solutions in specific polyols was measured in the single phase region as a function of shear rate and temperature via capillary rheometry. In addition, the viscosity of the same polyamide solutions containing various levels of dispersed, nanoscale calcium carbonate particles was characterized in order to understand the rheology of the filled systems. Viscosity-reduced shear rate master curves were constructed by applying the principle of time–temperature superposition, and the activation energies were measured for the polyamide-polyol solutions. The observed increase in viscosity caused by the addition of nanofiller could not be explained by simply applying a vertical shift to the master curve, and a density exponent was required to account for the stiffening mechanism. Also, the dependence of the relative viscosity on the filler loading was shown to be consistent with the hypothesis that the filler particles were organized in the form of small fractal aggregates. The filled polyamide 11 systems exhibited higher relative viscosities than the filled polyamide 12 systems, indicating a higher level of particle aggregation and larger mean cluster size for the filled polyamide 11 systems. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48244.     

Some properties of polyethylene compounds with surface-modified fillers

The dispersion of variously surface-treated CaCo³ fillers in linear low density polyethylene has been studied, along with mechanical properties of the filled compounds. Microwave plasma discharges were used to modify the filler surfaces. Inverse gas chromatographic analyses showed that plasma treatments could change the dispersive and non-dispersive components of filler surface characteristics. A reduction in these surface energies facilitated the dispersion of the filler in the non-polar polyethylene. Mechanical properties, particularly those at high deformation of the filled plastic, also responded to filler surface treatments, the ductility at failure increasing with a decrease in the filler's surface polarity. For any given elongation at failure, it was found that the amount of filler accommodated by the host polymer was raised by the appropriate surface modification procedure. The work illustrates the important contribution made by interfacial phenomena to various performance aspects of complex polymer systems.     

Dynamic rheological behavior of high‐density polyethylene filled with carbon black

The dynamic rheological behavior of high‐density polyethylene (HDPE) composites filled with carbon black (CB) was studied by controlling periodic small shear strains at constant temperatures. The results shed light on the relationship between the behavior of dispersed fillers and polymeric matrix systems. At sufficiently high filler concentration a structural skeleton seems to appear, which significantly raises the modulus at the low frequency region. High structure, finer size acetylene black raises the modulus significantly more than does the low structure and larger size one (e.g., N550). Oxidized CB increases the modulus in the whole frequency region for the enhanced interaction between polymer matrix and CBs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3527–3531, 2002     

Polymer composites containing plasma-treated mica. I. Flow and mechanical properties

Suzorite mica has been surface modified by microwave plasma treatment in ethylene gas. The surface-treated mica was used as a filler in polyethylene, polystyrene, and a mixture of these two polymers. Significant changes in rheological behavior ensue. These indicate that adhesion between polyethylene and irradiated mica is superior to that of interfaces using unirradiated mica. In contrast, ethylene irradiation reduces the ability of filled polystyrene compounds to store elastic energy in melt flow, an effect consistent with impaired adhesion at interfaces involving these components. An intermediate situation exists in the case of the two-polymer blend. The tensile properties of these systems also reflect surface treatment, reinforcement occurring in polyethylene-containing compounds, while the tensile properties of polystyrene composites deteriorate. Plasma-induced surface modifications of fillers to produce desired property changes in specified polymer matrixes are implied by the present work, but a fuller understanding of the chemistry of surface modification reactions is needed to substantiate these implications.     

无机化合物对填充PE薄膜性能影响的研究

以CaCO3、BaSO4、滑石粉为填料,以低密度聚乙烯(LDPE)为基体,通过共混、挤出工艺制得无机填充母粒,将填充母粒与LDPE、线性低密度聚乙烯(LLDPE)按一定比例混合,通过吹塑成型获得不同无机填料改性聚乙烯(PE)薄膜,并对其力学性能和光学性能进行了测试和分析.结果表明,CaCO3、BaSO4、滑石粉质量分数低于15%时,能增加PE薄膜的拉伸强度,而且BaSO4、滑石粉改性PE薄膜的光学性能比CaCO3改性PE薄膜效果好.     

Effect of volume loading and surface treatment on the thixotropic behavior of polypropylene filled with calcium carbonate

The rheological properties of calcium carbonate‐filled polypropylene were examined using a Rheometrics dynamic analyzer. The study included steady shear test, transient stress growth test with sequential deformation history, and two‐step dynamic oscillatory shear flow. Thixotropic behavior was observed in transient tests for highly filled compounds when volume loading exceeding a critical value at about 20%. The material responses of these viscoelastic thixotropic materials depend on the duration of shear as well as on the rate of shear. The effects of filler on the rheological behavior of highly filled compounds are dominant at low strain rates; however, the effects of activity of the filler are almost negligible at high strain rates because of complete breakdown of the filler network. The timescales for structural changes in filled systems often become long compared with the viscoealstic time constants of the unfilled melt. The magnitudes of rheological properties and the degree of hysteresis appear to increase with increasing volume loading of filler particles. Conversely, surface treatment of fillers, which presumably reduces interaction between filler particles and the extent of agglomeration, results in major reductions of both rheological properties and the degree of hysteresis. The diverse experimental observations are interpreted in terms of a system forming a filler network due to weak interparticle forces. The thixotropy resulting from breakdown and recovery of the filler network is dependent on the characteristic time of the individual test.     

Influence of untreated and novel electron‐beam‐modified surface‐coated silica filler on the thermorheological properties of ethylene–octene copolymer

We developed surface‐modified silica fillers by coating these with an acrylate monomer, trimethylolpropane triacrylate, or a silane coupling agent, triethoxyvinyl silane, followed by electron‐beam irradiation at room temperature. These were incorporated in an ethylene–octene copolymer rubber. Thermorheological studies of the unvulcanized ethylene–octene copolymer and its untreated and modified silica‐filled composites were done with a shear dynamic oscillating rheometer. Modification of the silica filler, especially via the silanization process followed by electron beam treatment, significantly reduced filler–filler networking as revealed from the log–log plots of storage modulus and complex shear viscosity, and its real component. The rheological complexity of the compositions was analyzed from a double logarithmic plot of the storage modulus and loss modulus. The results obtained from the master curves constructed on the basis of the time–temperature superposition principle and the activation energy calculated from the Arrhenius equation for the flow of above these compounds further supported these findings. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2453–2459, 2003     

Shear yield behavior of calcium carbonate–filled polypropylene

The rheological properties of calcium carbonate-filled polypropylene has been examined using a Rheometrics dynamic analyzer RDAII. The study included a steady shear test, a transient stress growth test, and a dynamic oscillatory shear flow. Yield behavior was observed in all kinds of rheological tests for highly filled compounds when the volume loading exceeded a critical value at about 20%. The empirical Cox-Merz rule, which is usually applicable to an unfilled polymer, was found to be invalid for highly filled compounds. The modified Cox-Merz rule, in which the apparent viscosity versus the shear rate is equal to the complex viscosity versus the frequency-amplitude in the nonlinear region, was found to be valid only for highly filled compounds. The viscosity and the apparent yield values appear to increase with increasing volume loading of filler particles. The surface treatment of fillers, which presumably reduces the interaction between filler particles and the extent of agglomeration, results in major viscosity reductions and decreases in apparent yield values. The yield values determined from various tests are not the same. The results are interpreted in terms of a system forming a filler network due to weak inter-particle forces. The yield stress resulting from the breakdown and recovery of the network is thus dependent on the characteristic time of the individual test.     

An investigation on wear behavior of UHMWPE/carbide composites at elevated temperatures

Ultra-high molecular weight polyethylene (UHMWPE) is extensively used in frictional applications due to its advanced wear resistance. This advanced polymer is reinforced with hard particulate fillers for further developments against wear conditions. Since elevated temperatures prevail in the service conditions, wear behavior of UHMWPE composites is an important issue for the engineering applications. In the present work, UHMWPE-based composites including silicon carbide (SiC) fillers were fabricated in a compression molding chamber. In the specimen preparation stage, molding pressure, filler amount, and filler particle size were varied to investigate the influence of these variables. Upon deciding the optimum parameters from the wear tests conducted at room temperature, the wear experiments were repeated for the optimum specimen at elevated temperatures, such as 40 and 60°C. According to the results, the wear behavior of the SiC/UHMWPE composites is heavily changed by the effect of elevated temperature. Adhesive effect is pronounced at elevated temperatures while the wear characteristics possess the abrasive effect in the sliding path. In addition, the composites exhibit an accelerated material loss as temperature increases during the frictional system.     

Effect of filler–filler interaction on rheological behaviour of natural rubber compounds filled with both carbon black and silica

Rubber compounds are reinforced with fillers such as carbon black and silica. In general, filled rubber compounds show smooth rheological behaviour in measurement of Mooney viscosity or Mooney scorch time. Variation in rheological behaviour was studied in terms of the filler composition using natural rubber compounds filled with both carbon black and silica (carbon black/silica = 60/20,40/40, and 20/60 phr). The compound filled with carbon black/silica of 60/20 phr showed normal rheological behaviour. However, the compounds filled with carbon black/silica of 40/40 and 20/60 phr showed abnormal rheological behaviour, in which the viscosity increased suddenly and then decreased at a certain point during the measurement. The abnormal behaviour was explained by the strong filler–filler interaction of silica. Moreover, the abnormal rheological behaviour was displayed more clearly as the storage time of compounds is increased. © 2003 Society of Chemical Industry     

Influence of untreated and novel electron beam modified surface coated silica filler on dynamic mechanical thermal properties of ethylene‐octene copolymer

An extensive study on dynamic mechanical thermal analysis has been carried out to investigate the effect of filler‐filler and polymer‐filler interaction in cured ethylene‐octene copolymer reinforced by unmodified and modified silica. The silica was treated with trimethylolpropane triacrylate (TMPTA) or triethoxyvinyl silane (TEVS), followed by electron beam irradiation at room temperature. Modification of the silica filler, especially via silanization, significantly reduces filler‐filler networking, as evidenced from the strain sweep tests, and thus helps reduce the Payne effect, particularly at high filler loadings. The effect of modification is quantified with the help of a new mathematical model correlating the storage modulus and the volume fraction of the filler. The enhancement in the storage modulus at high temperatures and changes in the loss tangent at the glass transition temperature suggest definite improvement in the polymer‐filler interaction in the case of these modified fillers. The results obtained from the master curves constructed based on the time‐temperature‐superposition principle further support the findings.     

用改进的Herschel-Bulkley模型描述EPDM胶料的流变行为

采用平行板旋转流变仪测定炭黑/碳酸钙填充EPDM胶料不同温度下的流变性能。应用时温叠加原理得到胶料的流变主曲线,选用修改后的Herschel-Bulkley模型拟合主曲线。结果表明,修改后的Herschel-Bulkley模型能够较好地描述不同牌号EPDM胶料的非线性流变行为,同时确定了一系列模型相关参数。     

Effect of UV light,electron beam and gamma irradiation on capillary flow of LLDPE and LLDPE filled with sericite–tridymite–cristobalite

Abstract

The rheological properties of linear low density polyethylene (LLDPE) were modified by irradiation in order to reduce or eliminate the unstable region (spurt) on the flow curve. Three different types of irradiation source (gamma ray, electron beam and UV light) were used to introduce the oxygen-containing groups into molecular chains of LLDPE, and consequently attain chain scission without any chemical additives resulting in smooth flow without any evidence of instability. This was proved by FTIR and contact angle measurements. Further, irradiation treatment should lead to increased polarity of polyethylene, and thus to increased adhesion between the polymer and polar fillers. Therefore, LLDPE filled with sericite–tridymite–cristobalite (STC) was investigated. Although the viscosity changes were rather negligible, a positive effect was seen during mixing, where torque, necessary to disperse the powder homogeneously in the polymer melt, was dramatically reduced, especially in the case of gamma-irradiated samples.     

Estimation of the melt rheology of polymer waste from melt flow index

The need for recycling of polymeric waste has been well recogmized as a result of the escalating prices of the petrochemical feedstocks and the growing awareness to curtail solid waste that causes environmental pollution. During processing, the molecular weight of the polymer is reduced due to thermal and shear degradation. Since the melt rheology of the processed material is sensitive to the changes in molecular structure, knowledge of the complete flow curve depicting the variation of melt viscosity with shear rate at processing temperatures is a useful tool for assessing the reprocessibility of waste material and for specifying the conditions of reprocessing. In the present paper, an effective method is proposed to generate the melt flow curves of polymer waste from knowledge of its melt flow index. The method makes use of a master curve that can be obtained by plotting the available viscosity data in terms of modified functions based on the melt flow index. The master curves characteristic of the particular generic resin type are presented for low-density polyethylene, polypropylene and polystyrene.