Lower Melt Flow Index Research Articles

A Study of the Mechanical Behavior and Crystal Structure of UHMWPE/HDPE Blend Fibers Prepared by Melt Spinning

Ultrahigh molecular weight polyethylene (UHMWPE) and high-density polyethylene (HDPE) blend fibers with the highest tensile strength of 1.13 GPa were prepared by a melt spinning process. The crystal structure and mechanical behavior of the as-spun filaments and fibers were studied by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), atomic force microscope (AFM), X-ray diffraction (XRD), sound velocity orientation test and tensile strength test. The results suggested that the degree of molecular chain orientation, crystallinity and mechanical properties of the blend fibers were improved by blending with the low melt flow index (MFI) HDPE. The crystal grains of low MFI HDPE blend fibers that were formed by more highly oriented molecular chains could be stretched more effectively in the drawing direction, and the improved mechanical properties were due to the more regular and compact crystal structure.

Hybrid composites of ABS with carbonaceous fillers for electromagnetic shielding applications

ABSTRACTThis work evaluates the influence of two types of carbonaceous fillers, carbon black (CB) and carbon nanotubes (CNTs), on the electrical, electromagnetic, and rheological properties of composites based on poly(acrylonitrile‐co‐butadiene‐co‐styrene) (ABS) prepared by the melt mixing. Electrical conductivity, electromagnetic shielding efficiency (EMI SE) in the X‐band frequency range (8–12.4 GHz), and melt flow index (MFI) results showed that ABS/CNT composites exhibit higher electrical conductivity and EMI SE, but lower MFI when compared to ABS/CB composites. The electrical conductivity of the binary composites showed an increase of around 16 orders of magnitude, when compared to neat ABS, for both fillers. Binary composites with 5 and 15 wt % of filler showed an EMI SE of, respectively, −44 and −83 dB for ABS/CNT, and −9 and −34 dB for ABS/CB. MFI for binary composites with 5 wt % were 15.45 and 0.55 g/10 min for CB and CNT, respectively. Hybrid composites ABS/CNT.CB with 3 wt % total filler and fraction 50:50 and 75:25 showed good correlation between EMI SE and MFI. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46546.

3D Printable Filaments Made of Biobased Polyethylene Biocomposites.

Two different series of biobased polyethylene (BioPE) were used for the manufacturing of biocomposites, complemented with thermomechanical pulp (TMP) fibers. The intrinsic hydrophilic character of the TMP fibers was previously modified by grafting hydrophobic compounds (octyl gallate and lauryl gallate) by means of an enzymatic-assisted treatment. BioPE with low melt flow index (MFI) yielded filaments with low void fraction and relatively low thickness variation. The water absorption of the biocomposites was remarkably improved when the enzymatically-hydrophobized TMP fibers were used. Importantly, the 3D printing of BioPE was improved by adding 10% and 20% TMP fibers to the composition. Thus, 3D printable biocomposites with low water uptake can be manufactured by using fully biobased materials and environmentally-friendly processes.

Selection of ethylene-vinyl-acetate properties for modified bitumen with enhanced end-performance

Bitumen modification with ethylene-vinyl acetate (EVA), in a wide range temperatures (between − 30 and 100 °C), has been studied as a function of polymer concentration and EVA characteristics (vinyl acetate (VA) content and melt flow index (MFI)). Viscous flow, dynamic shear (DSR) temperature sweep, and technological tests were conducted to assess binder performance at medium-to-high in-service temperatures. Evaluation of binder low-temperature viscoelastic behavior has been performed using a solid rectangular fixture (SRF) in torsional mode, either in the linear viscoelastic region or under non-linear conditions (by strain breakage tests between − 30 and 0 °C). Further microstructural analysis based on modulated differential scanning calorimetry (MDSC) and optical microscopy was conducted to support rheological and technological results. Hence, total crystalline fraction (related to the VA content and polymer concentration) turned out to be a key parameter to achieve a suitable binder modification at medium-high temperatures. In addition, MFI appears to be an important EVA parameter at low temperatures, as it was found that lower MFI values enhanced resistance to low-temperature cracking.

Preparation, mechanical properties and microstructure of polyoxymethylene fiber through melt spinning and hot drawing by using injection-molding grade resins

The polyoxymethylene (POM) fiber was melt spun by use of different commercial grades of POM resin, and the effect of post-drawing on mechanical properties and microstructures was investigated extensively. The fiber obtained from the POM resin with a higher melt flow index (MFI) exhibits a better hot-drawing capability and also achieves a greater ultimate draw ratio. The mechanical evaluation reveals that the tensile strength and elastic modulus of POM fiber are improved significantly after post-drawing compared to the as-spun fibers. Although the greater draw ratios result in higher mechanical strength and modulus for the POM fiber, the fiber obtained from the POM resin with an MFI of 13.0 g/10 min achieves the optimal mechanical performance at the ultimate draw ratio. The morphologic and structural developments of POM fiber were studied by scanning electronic microscopy and X-ray powder diffraction. The results indicate that the POM fiber spun by the resin with an MFI of 13.0 g/10 min has a smooth lateral surface and a compact cross section after post-drawing. The fiber samples spun by the POM resins with low MFIs show some hollow disfigurements as well as a rough surface at the ultimate draw ratio, whereas the fiber obtained from the resin with a high MFI of 27.0 g/10 min presents the ununiformity of diameter after post-drawing. The POM fibers achieve a crystalline orientation during the hot-drawing process, which results in a transformation from the spherulitic crystals to the lamellar structure in the drawing direction. The level of crystalline orientation can be improved with an increase of draw ratio and thus results in a high modulus and strength for the resulting POM fiber samples. In addition, the thermal analysis indicates that the crystallinity of the as-spun fibers can be enhanced by post-drawing due to the orientation-induced crystallization.

Rheological and Thermal Study of Chitosan Filled Thermoplastic Elastomer Composites

The chitosan filled thermoplastic elastomer (TPE) composites with different filler loading was prepared by melt mixing at 180 °C. The effect of 3-aminopropyltriethoxysilane (3-APE) as coupling agent on the rheological and thermal properties of composites were investigated. The melt flow indexer was used to characterize the melt flow index (MFI) of TPE/Chitosan composites at temperature of 180 to 210 °C. It was found that addition of chitosan into composites had reduced the MFI values. Besides that, the MFI values of composites were found to increase linearly with temperature. The treated composites demonstrated lower MFI values, indicated that better interfacial bonding was established between chitosan and TPE and the flowability of the composite melts was hindered. The TGA results reported that the treated composites had better thermal stability and lower total weight loss as compared to untreated composites at similar filler loading.

Rheological, morphological and mechanical properties of flax fiber polypropylene composites: influence of compatibilizers

In this work, the rheological, mechanical and morphological properties of flax fiber polypropylene composites were investigated. The effect of incorporating a polypropylene grafted acrylic acid or a polypropylene grafted maleic anhydride on these properties has been studied as well. According to scanning electron microscopic observations and tensile tests, the addition of a compatibilizer improved the interfacial adhesion between the flax fibers and the polymer matrix. The tensile modulus of composite containing 30 wt% flax fibers was improved by 200 % and the tensile strength improved by 60 % in comparison with the neat PP. Plasticizing effect of the compatibilizers as a result of their lower melt flow index was also shown to decrease the rheological properties of the composites, even though the effect was not pronounced on the mechanical properties.

Synthesis and Thermomechanical and Rheological Properties of Biodegradable Long-Chain Branched Poly(butylene succinate-co-butylene terephthalate) Copolyesters

Biodegradable long-chain branched (LCB) poly(butylene succinate-co-butylene terephthalate) (PBST) copolyesters were prepared via a two-step direct esterification and melt polycondensation process, using a small amount (0–2 mol %) of diglycidyl 1,2,3,6-tetrahydrophthalate (DGT) as an in situ branching agent (BA). The chemical structures of LCB PBSTs were characterized and the thermal, mechanical, and rheological properties were investigated. With increasing DGT loading, PBSTs with higher branching degree, broader molecular weight distribution, and lower melt flow index were synthesized in shorter polycondensation time. The branching of PBSTs results in a slight decrease in crystallizability, melting, and Vicat softening temperatures, but leads to an obvious decrease in elongation at break. On the other hand, the existence of LCB greatly improved the rheological properties of PBSTs. PBST with higher branching degree possesses higher storage and loss modulus, higher zero-shear viscosity, longer relaxation ti...

Estudo experimental do processo de rotomoldagem de PELBD: efeitos sobre a morfologia e estabilidade dimensional

No presente estudo o empenamento de peças de polietileno linear de baixa densidade (PELBD) moldadas por rotomoldagem foi investigado. O efeito de diferentes fatores como espessura da peça, taxa de resfriamento e diâmetro de tubo de ventilação foi avaliado. Além dos experimentos de rotomoldagem, uma técnica alternativa denominada "Hot Press" foi também aplicada para investigar o empenamento de dois diferentes PELBD sob condições típicas da rotomoldagem quanto ao resfriamento assimétrico. Cristalinidade e morfologia esferulítica ao longo da espessura das peças rotomoldadas foram avaliadas por Calorimetria Exploratória Diferencial (DSC) e Microscopia Ótica de Luz Polarizada. Verificou-se que o grau de empenamento aumenta com a taxa de resfriamento. O aumento do diâmetro do tubo de ventilação é mais efetivo na redução do empenamento principalmente em menores taxas de resfriamento. Nos experimentos de "Hot Press" o PELBD com menor índice de fluidez e maior módulo de flexão apresentou menor empenamento. Nos experimentos de "Hot Press" a espessura das peças afetou o empenamento somente para maiores taxas de resfriamento. Em geral, a cristalinidade e o tamanho de esferulitos se mostraram menores nas posições ao longo da espessura das peças rotomodadas onde as taxas de resfriamento eram mais rápidas.

Effect of the melt flow index and melt flow rate on the thermal degradation kinetics of commercial polyolefins

AbstractIn this study, several polyolefins, including different grades of polypropylene (PP), high‐density polyethylene, linear low‐density polyethylene, and low‐density polyethylene, were tested by thermogravimetric analysis (TGA), and the relationships of their melt flow index (MFI) and melt flow ratio (MFR) values to the thermogravimetry (TG) curves, differential thermogravimetry (DTG) curves, and activation energy of thermal degradation were investigated. Kinetic evaluations were performed by Friedman and Kissinger analysis methods, and the apparent activation energy values for the overall degradation of different grades of polyethylenes (PEs) and PPs were determined. We found that for the samples with lower MFIs, the thermograms shifted to higher temperatures. Meanwhile, a higher activation energy was needed for their thermal degradation. Also, for samples with higher values of MFR, as a means of molecular weight distribution, a lower activation energy was needed for their thermal degradation, and their TGA thermograms shifted to lower temperatures. The breadth of the DTG curves depended on the MFR in the PEs, although MFR had little effect on the DTG curves in the studied PP grades. Among all of the samples studied, the injection‐molding grades with medium MFIs and low MFRs degraded at higher temperatures and showed better thermal stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012

Factorial optimisation of the effects of extrusion temperature profile and polymer grade on as-spun aliphatic–aromatic co-polyester fibres III: mechanical properties

The effect of extrusion temperature profile in the melt‐spinning process of as‐spun linear aliphatic–aromatic co‐polyester (AAC) fibres upon their mechanical properties and process productivity was modelled by using factorial experimental designs. After the viscoelastic and morphology characteristics of the polymer were considered using Differential Scanning Calorimetry and Melt Flow Index (MFI), the rheological data were used to determine the enhanced melt‐spinning temperature of the six heating zones in the process. Tensile strength, elongation at break, modulus and fibre productivity (g/min) of the melt‐spinning process have been quantitatively assessed as responses to polymer grades and extrusion zone temperature. The optimisation of mechanical properties and productivity helps in understanding and controlling the most desired properties in the produced fibre. It has been noted that the die head temperature (spinning temperature), the polymer grade and their interaction are the most significant factors affecting the mechanical properties. Analysis of the fibre productivity shows that the polymer grade and its interaction with the die head temperature is significant in terms of influencing the output of the melt‐spinning process, which could be related to the polymer molecular weight and polymer structure. There is an interaction between polymer grade and feeding zone temperature which is related to the material supply action in the feeding zone. The friction between the screw and the material is affected by heating action, which affects the moisture content and the molten material rheology. By adjusting the extrusion temperature profile and selecting the more applicable spin‐able polymer grade through a statistical forecasting model, the combination of the cost related to material grade and processing cost controls the fibre production cost. The fibre made of low MFI grade has better structure and mechanical properties than that made of the higher MFI grade, and the former will be preferred for future work. With previous work related to the effects of extrusion temperature profile on the fibre structure, the present paper will help in developing the production process of biodegradable linear AAC fibres.

Factorial Optimisation of the Effects of Melt Spinning Conditions on Biodegradable As-spun Aliphatic-Aromatic Co-Polyester Fibres

Abstract In order to optimize the melt spinning process of biodegradable as-spun linear aliphatic-aromatic co-polyester fibres, a fractional factorial experimental design and appropriate statistical analysis for the thirty-two screening trials involving five control parameters were used. Depending on previous studies (Younes and Fotheringham, 2011a, Younes, et al., 2009, 2010, Younes, et al., 2011b), the low melt flow index grade has been utilized in this work. Die head pressure of the extrusion machine, a range of crystallographic orders presented as full-width half-maximum of an X-ray scattering of as-spun fibres and thermo-graphic measurement of extruded filament in the air quench cooling window were investigated. Statistical analyses explained the relationship between, on the one hand, throughput flow rate and spinning temperature of filaments and, on the other hand, the crystallographic structure of the as-spun filaments. It has been found that spinning temperature and metering pumps speed are by far the most important factors affecting the die head pressure. Low spinning temperature leads to higher viscosity, higher flow resistance through the spinneret's nozzle and high die head pressure. Crystallographic order is affected significantly by metering pump speed, and the interaction between spinning temperature and quench air cooling speed. Metering pump speed, spinning temperature, winding speed and quench air cooling speed affect the filaments' temperature average. The obtained optimization helps to produce the most satisfactory properties in the biodegradable fibre based textiles, as environmentally-friendly attractive materials alternative to commercial chemical fibres for different applications.

Factorial Optimization of the Effects of Melt-Spinning Conditions on As-spun Aliphatic-Aromatic Copolyester Fibers I. Spin Draw Ratio, Overall Orientation and Drawability

According to our previous studies [1,2], the optimum melting conditions have been achieved and lower melt flow index grade has been utilized in this work. In order to characterize the melt-spun AAC fibers, spin-draw ratio, optical birefringence and drawability were measured. The statistical optimization of fiber properties helps to produce the most satisfactory properties in the final fibers as an environmentally friendly attractive alternative to commercial chemical fibers. The importance of this model is in controlling the production process to optimize and enhance fiber properties, which may improve the quality and cost of biodegradable fibers.

Influence of polyfunctional monomer on melt strength and rheology of long‐chain branched polypropylene by reactive extrusion

AbstractLong chain branching (LCB) were added to linear polypropylene (PP) using reactive extrusion in the presence of selected polyfunctional monomers (PFMs) and a peroxide of dibenzoyl peroxide (BPO). Fourier Transformed Infrared spectra (FTIR) directly confirmed the grafting reaction occurred during the reactive extrusion process. Various rheological plots including viscosity curve, storage modulus, Cole‐Cole plot, and Van‐Gurp plots, confirmed that the LCB structure were introduced into modified PPs skeleton after modification. In comparison with linear PP, the branched samples exhibited higher melt strength, lower melt flow index, and the enhancement of crystallization temperature. The LCB level in modified PPs and their melt strength were affected by the type of PFM used and could be controlled by the PFM properties and structure. PFMs with lower boiling points, such as 1, 4‐butanediol diacrylate (BDDA), could not produce LCB structure in modified PP skeleton. The shorter molecular chain bifunctional monomers, such as 1,6‐hexanediol diacrylate (HDDA), favored the branching reaction if their boiling points were above the highest extrusion temperature. And some polar groups, such as hydroxyl, in the molecule of PFM were harmful to the branching reaction, which might be attributed to the harm of the polarity of groups to the dispersion of PFM in PP matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Thermal characterization of the HDPE/LDPE blend (10/90) irradiated using γ-rays

Gamma irradiation effect over the properties of slow cooled and fast cooled HDPE/LDPE 10/90 blend was studied. The blend and the neat polyethylenes were irradiated at room temperature in the presence of air using the following doses (4.8 kGy/h): 0, 50, 150, 400 and 1000 kGy. Differential scanning calorimetry (DSC) experiments were carried out using the following heating rates: 5, 10 and 20 °C/min. DSC results for the slow and fast cooled blend showed traces with three melting peaks and with increasing irradiation dose two melting peaks were obtained, i.e. the high melting peak shifts toward lower temperatures to merge with the intermediate melting peak into one endotherm. No changes in crystal structure by X-ray diffraction were found as a result of samples irradiation. Radiation crosslinking prevents crystal rearrangements during heating in the DSC. Gel content and melt flow index (MFI) measurements showed that radiation induced a high degree of crosslinking for all samples; gel content values were above 50% and a drop of more than 90% in the MFI was found. Irradiation of slow cooled samples resulted in larger values of gel content and lower MFI values than for fast cooled samples, mainly because of the higher degree of crosslinking for the former.

Rheology and melt strength of long chain branching polypropylene prepared by reactive extrusion with various peroxides

AbstractLong Chain Branching Polypropylenes were prepared in an extruder by a melt grafting reaction in the presence of various peroxides and a polyfunctional monomer of 1,6‐hexanediol diarylate. Fourier Transformed Infrared spectra and the rheological characteristics indicated that the grafting reaction added long branched chains to linear polypropylene (PP). In comparison to the initial PP, the branched samples exhibited higher melt strength, lower melt flow index, and enhancement of crystallization temperature. The branching number of the modified samples agreed well with their melt viscoelasticity and the improved degree of their melt strength. The branching level in modified PPs could be controlled by the property and structure of the peroxide used. Peroxides with lower decomposition temperature and more stable radicals after decomposition promoted the branching reaction, leading to the modified PPs with higher branching level and melt strength. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

The characterization of rheological properties of melt grafting polypropylene for foaming

Large enhancements of the melt strength of polypropylene (PP) were achieved by the introduction of specific unsaturated linear polyester (ULP) branches using melt grafting. The transient torque curves and optical rheology microscope images indicated that branching reactions took place and the ULP had been grafted onto the PP backbone. Shear rheological behaviors of three kinds of PP were investigated using rotational rheometer under dynamic shear mode with periodic shear rate. These PP samples are foamable PP (FPP) with sparse branches obtained by grafting ULP, commercial high melt strength PP (HMS PP) for foaming and conventional linear PP (EPS). It was found that the rheological properties of FPP, the HMS PP, were distinctly different from those of conventional PP. Storage modulus, steady state compliance and zero shear viscosity increased in comparison with EPS, while shear viscosity decreased. This result implied the presence of branching structures that was not revealed in conventional PP. In melt flow measurements, extrusion swell that was a prominent behavior of branching PP was observed also for FPP and PF. Compared to linear PP, FPP and PF showed distinct sag-resistant property and lower melt flow index. On the other hand, to estimate the extent of branching, a detailed method was applied using the obtained zero shear viscosity. The result showed that FPP was grafted by sparse ULP. From these results, it was found that FPP showed obvious enhancements in rheological behaviors similar to PF, although its melt strength was lower than that of PF due to the presence of shorter branching chains grafted on the backbone of FPP.

Toughening of recycled polystyrene used for TV backset

AbstractThe recycled polystyrene (rPS) was toughened with ethylene‐octylene copolymer thermoplastic elastomer (POE) and high‐density polyethylene (HDPE) with various melt flow index (MFI), compatibilized by styrene‐butadiene‐styrene copolymer (SBS) to enhance the toughness of rPS for use as TV backset. The rPS/POE binary blends exhibited an increased impact strength with 5–10 wt % POE content followed by a decrease with the POE content up to 20 wt %, which could be due to poor compatibility between POE and rPS. For rPS/POE/SBS ternary blends with 20 wt % of POE content, the impact strength increased dramatically and a sharp brittle‐ductile transition was observed as the SBS content was around 3–5 wt %. Rheological study indicated a possible formation of network structure by adding of SBS, which could be a new mechanism for rPS toughening. In rPS/POE/HDPE/SBS (70/20/5/5) quaternary blends, a fibril‐like structure was observed as the molecular weight of HDPE was higher (with lower MFI). The presence of HDPE fibers in the blends could not enhance the network structure, but could stop the crack propagation during fracture process, resulting in a further increase of the toughness. The prepared quaternary blend showed an impact strength of 9.3 kJ/m2 and a tensile strength of 25 MPa, which can be well used for TV backset to substitute HIPS because this system is economical and environmental friendly. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Low-dimensional models for describing mixing effects in reactive extrusion of polypropylene

Spatially averaged low-dimensional models based on Liapunov–Schmidt technique of bifurcation theory have been developed to study mixing effects in peroxide-induced reactive extrusion of polypropylene degradation. The two-dimensional convection–diffusion-reaction equations for each species and the energy balance equation have been averaged in the transverse direction to obtain low-dimensional models that describe transverse (local) mixing effects on conversion, average molecular weight and temperature distribution in a reactive extruder channel with asymmetric thermal boundaries. Our models predict that incomplete local mixing due to velocity distribution, backflow and transverse diffusion may significantly reduce the conversion (by more than 50%) in a reactive extruder, compared to a plug-flow case. Our analysis further reveals that beyond a transition value of Damköhler number ( Da), the overall reaction occurs in the mixing-limited regime, where the conversion and the average molecular weight of the polymer melt are determined only by the dimensionless local mixing time (which, in turn, depends on the screw speed) and are independent of Da. Increased Graetz number (i.e. slow transverse thermal diffusion) decreases the polymer-melt temperature and reduces conversion, while increase in screw speed increases viscous heat generation resulting in higher exit temperature accompanied by reduced conversion and produces off grade high molecular weight (low melt flow index) product when the mixing effect dominates the temperature effect.

The influences of fiber feature and polymer melt index on mechanical properties of sugarcane fiber/polymer composites

AbstractThe fiber characteristics (i.e., the fiber type, morphology, and dimension) and polymer melt flow index (MFI) significantly affected mechanical properties of sugarcane fiber/HDPE composites. The length and diameter of sugarcane fibers followed a lognormal distribution before and after compounding. The long fibers had a significant reduction in the dimension and aspect ratio during compounding. However, the short fibers had close values in these two properties before and after compounding. For the resultant sugarcane fiber/polymer composites, the HDPE resins with a low MFI value presented high tensile and impact strengths. Because of high sugar content, the pure rind fiber had a poor performance as filler in the HDPE resins with respect to the raw bagasse fiber and alkali‐extracted bagasse fiber. On the other hand, the aspect ratio was proportional to the mechanical performance of the fibers in the HDPE resins. As a result, the fibers with a large aspect ratio and low sucrose content improved the strength properties of the resultant composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5607–5619, 2006