Thermokinetic Mixer Research Articles

Mechanical Behaviour of Polypropylene Reinforced Palm Fibers Composites

Nowadays, a great attention has been dedicated to natural fibers as reinforcement for polymers. Natural fibers, compared to glass fibers, exhibit better mechanical properties, such as stiffness, impact strength, flexibility and modulus. However certain drawbacks, such as the incompatibility between fibers and polymer matrices, the tendency to form aggregates during processing and the poor resistance to moisture, reduce the use of these natural fibers as reinforcements in polymers. Several treatments and modifications are being used to improve fibers/matrix compatibility, such as bleaching, acetylation and use coupling agent. In this work, the effect of coupling agent in the palm fibers/ PP composites was evaluated on mechanical behaviour. Palm fibers were mixed with the polymeric matrix (PP) in a thermokinetic mixer, with speed rate maintained at 5250rpm, in which fibers were responsible for 5 wt% in the composition. When the coupling agent was used, the proportion of PP was 95 wt% and the coupling agent was 5 phr. After the mixture, composites were dried, ground in mill and placed in an injector camera according to ASTM D-790 specification. Results showed that, the addition of coupling agent in the composites improved significantly the flexible strength and modulus when compared to the pure polymer.

Mechanical behaviour of polypropylene reinforced sugarcane bagasse fibers composites

Recently the interest in composite materials reinforced with natural fibers has considerably increased due to the new environmental legislation as well as consumer pressure that forced manufacturing industries to search substitutes for the conventional materials, e.g. glass fibers. This way, the objective of paper was evaluate the effect of chemical modification on mechanical properties of sugarcane bagasse fiber/PP composites. Fibers were pretreated with 10% sulfuric acid solution, followed by delignification with 1% sodium hydroxide solution. These fibers were mixed with the polypropylene in a thermokinetic mixer, and compositions with 5 to 20 wt% of fibers were obtained. The mechanical properties were evaluated by means of tensile, 3-point bending and impact tests. In addition, fracture analysis via SEM (secondary electrons mode) was performed. Results showed improve the tensile, flexural and impact strength of the composites in comparison to the polymer pure.

Eigenschaften von extrudierten Holz-Kunststoff-Werkstoffen auf Basis von Refiner-(TMP-)Fasern und Hanffasern

At present, wood particles (wood flour) with a low aspect ratio are mostly used as fillers in wood-plastic composites (WPC). Reinforcement of WPC and improved strength properties may be achieved by using real wood fibres with a high aspect ratio. WPC based on 70% (wt.) refiner (TMP) wood fibres and mechanically processed hemp fibres were extruded in a two-step process. Eleven compounds based on the two natural fibre types were prepared using a thermokinetic mixer and extruded in a conical, counter-rotating twin-screw extruder. Additional formulation components were polypropylene fibres, maleic anhydride-modified polypropylene (MAPP) and lubricant. It was determined that compounding in a thermokinetic mixer is a useful step for processing of WPC with refiner and hemp fibres as little fibre damage occurred. However, during extrusion, both natural fibre types were severely shortened due to strong shear forces, and homogeneous dispersion of fibres in the matrix was not achieved. WPC based on hemp fibres displayed the best strength properties of the formulations tested. Current extruder screw and die configurations need to be modified to achieve improved fibre reinforcement and to create new, structurally demanding applications for WPC. Using dynamic mechanical analysis, fibre-matrix adhesion of WPC was investigated, and activation energies for glass transition of selected formulations were calculated. Activation energy for formulations containing MAPP was higher than for WPC without MAPP. This indicates that better fibre-matrix adhesion was achieved in formulations with MAPP.

Thermoplastic polyolefins as formaldehyde free binders in highly filled lignocellulosic panel boards: using glycerine as a processing aid in kenaf fiber polypropylene boards

A new technique was developed to make highly loaded (up to 95%) formaldehyde free natural fiber boards. The purpose of the paper is to report a broad study on 85% kenaf boards using linear thermoplastic polymers as the binder in preparing the boards to determine if these materials have potential in commercial applications by comparing them to other commercial materials. In these materials, linear thermoplastic polymer chains act as an adhesive and the product resembles a typical wood based panel (e.g., phenol formaldehyde fiber board). The process involved the use of small amount of glycerine in the fiber to enhance processibility in a thermo-kinetic mixer followed by hot pressing. In this paper, we report the properties of 85% by weight kenaf fiber boards using polypropylene as the adhesive. A maleated polypropylene was used to improve the adhesion and stress transfer between the adhesive and kenaf fiber. The addition of 2% by weight of glycerine based on the dry weight of kenaf fiber resulted in the best properties of the boards. Differential scanning calorimetric studies suggested that the glycerine had a little effect on the percent crystallinity of the matrix. Dynamic mechanical tests of the 85% boards showed some differences compared to conventional 60% by weight kenaf-PP composites. The 85% kenaf boards had a flexural strength of 75 MPa and a flexural modulus of 6.8 GPa with a specific gravity of 1.24. These properties are comparable to standard formaldehyde free high density hardboards with flexural strengths of 48.3 MPa and flexural modulus of 5.5 GPa, and a specific gravity of 1.28. This paper gives a broad overview of an initial study of these new materials.

Preparation and properties of HDPE/sugarcane bagasse cellulose composites obtained for thermokinetic mixer

The use of natural fibers as reinforcement for thermoplastics has generated much interest due to their low cost, possibility of environmental protection and use of locally available renewable resources. In this work the mechanical and morphological properties of high density polyethylene/pre-treated and modified residues from sugarcane bagasse cellulose composites were analyzed. Composites were produced by a thermokinetic mixer. The microstructural analyses of fracture surface from composites can be easily evaluated by microscopic techniques. Results showed that the modification of sugarcane bagasse cellulose with zirconium oxychloride was successfully accomplished and that this reinforcement material with high density polyethylene showed tensile strength higher than non-modified sugarcane bagasse cellulose. Modification in the sugarcane bagasse cellulose influenced directly in mechanical properties of the composite material. This can be observed by the fracture surface, which showed that modified cellulose sugarcane bagasse improved interfacial adhesion between fiber and matrix.

Study of utilizing thin polymer surface coating on the nanoparticles for melt compounding of polycarbonate/alumina nanocomposites and their optical properties

This paper presents a thin polymer surface coating approach to facilitate dispersion of poly(styrene-maleic anhydride) (SMA) copolymer-coated alumina (Al 2O 3) nanoparticles in polycarbonate (PC) using a high intensity thermokinetic mixer (K-mixer) and the optical properties of the resultant nanocomposites. Electron spectroscopy for chemical analyses (ESCA), energy filtered transmission electron microscopy (EFTEM), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FESEM) were used to investigate the covalent bonding of polymer coating on the nanoparticles and the nanoparticle dispersion. The light transmittance of the PC/alumina nanocomposites was measured and compared with that of the transparent neat resin.

Mechanical and heat deflection properties of PVC/PMMA/montmorillonite composites

AbstractComposites based on PVC were compounded with 5% of montmorillonite and 10% of PMMA. Two types of reinforcement were studied, which included a purified sodium montmorillonite and a montmorillonite organically modified with an alkylammonium chloride. The composites were compounded with a Gelimat type thermokinetic mixer and were ejected at a maximum temperature of 180°C. The organically modified montmorillonite discolored the PVC, result which was interpreted as a sign of chemical degradation caused by the alkylammonium modifier. The composite made with 5% of purified montmorillonite and 10 of % PMMA displayed the best overall properties. The most important improvement was obtained on flexural strain at break (0.097–0.175 mm/mm) and maximum flexural strength (62–76 MPa). The HDT increased by up to 8°C. Dynamic mechanical analysis showed that 10% of PMMA in PVC moved the tan δ peak to temperatures 5–6°C higher. The PMMA was completely miscible in PVC and played an important role in the montmorillonite dispersion, as observed by XRD and SEM analysis. It also contributed to the overall increase in properties of PVC/PMMA/montmorillonite composites. J. VINYL ADDIT. TECHNOL., 13:91–97, 2007. © 2007 Society of Plastics Engineers.

Modelagem de misturas na fabricação de compósitos polímero-fibra, utilizando polietileno e serragem de Pinus sp.

Neste trabalho, foi estudado o efeito da composição de diferentes misturas de polietileno de alta densidade (HDPE) virgem, HDPE reciclado e serragem de Pinus sp., nas propriedades físico-mecânicas de placas confeccionadas pelo processo de compressão. As misturas foram homogeneizadas em um misturador tipo Drais, sem controle de temperatura e moldadas por compressão em prensa hidráulica a 150oC. Partindo das placas, foram confeccionados corpos-de-prova para ensaios de tração, flexão, impacto e dureza, segundo normas ASTM, e também foram determinadas as densidades médias das placas. A modelagem estatística foi realizada segundo o planejamento centróide simplex, utilizando sete misturas dos três componentes e três repetições de cada mistura. Os resultados mostraram que a resistência à tração, a resistência à flexão, a dureza e a densidade das placas, são explicadas pelo modelo linear, enquanto a resistência ao impacto é explicada pelo modelo quadrático. Não houve diferença significativa nas propriedades físico-mecânicas dos compósitos confeccionados com HDPE virgem, daqueles confeccionados com HDPE reciclado, exceto para resistência ao impacto, no qual o HDPE virgem apresentou maiores valores.

Properties and Crystallization of Maleated Polypropylene/Graphite Flake Nanocomposites

Polypropylene (PP)/graphite (G) hybrid nanocomposites have been prepared by melt mixing using maleated PP (PP-g-MA) and graphite oxide (GO) as compatibilizing agents. Melt mixing was achieved using a Gelimat, a high-speed thermo-kinetic mixer. The PP-g-MA and GO used as compatibilizers helped the dispersion of the graphite on a nano-scale and improved flexural properties but more significantly the impact strength of the material. TEM micrographs showed a partial exfoliation of the graphite in the PP/PP-g-MA/GO/G hybrid nanocomposites. SEM micrographs of etched nanocomposite samples showed a fine grain micron-sized structure, while pure PP was characterized by larger 3-dimensional spherulites. Non-isothermal crystallization kinetics of PP and PP/PP-g-MA/GO/G nanocomposites were investigated by differential scanning calorimetry (DSC). The crystallinity and crystallization temperature of the nanocomposites were higher than for neat PP. Using the Kissinger model, the activation energy of crystallization of the nanocomposites was determined to be lower than PP. Models by Ozawa and Liu et al. were used to analyze and describe the non-isothermal crystallization kinetics. Overall, results indicate that the type of nucleation, growth and geometry of PP crystals markedly change in the presence of nano-sized graphite particles.

Compósitos de HDPE com resíduos de fibras têxteis. Parte I: caracterização mecânica

Neste trabalho são apresentados e discutidos os resultados das propriedades mecânicas de novos materiais compósitos preparados com resíduos de fibras têxteis poliméricas e de polímeros commodities. As fibras naturais oferecem vantagens sobre as sintéticas, em termos de propriedades mecânicas e térmicas. Os compósitos foram preparados a partir da mistura de polietileno de alta densidade (HDPE) e resíduos de fibras têxteis (50% algodão /50% acrílico) em teores crescentes de 10 a 40%, em um misturador de alta velocidade, utilizando Surlyn 2601, Polybond 3009 e Polybond 1009 como agentes compatibilizantes. Corpos-de-prova para ensaios de tração, flexão e impacto foram produzidos a partir de chapas obtidas em uma prensa hidráulica. Os compósitos que utilizaram agentes compatibilizantes apresentaram os melhores resultados de resistência à tração e à flexão, principalmente com 5% do agente Polybond 3009 e 20 a 40% de resíduos de fibras têxteis.

Compounding of nanocomposites by thermokinetic mixing

AbstractNanocomposites have been prepared by melt mixing poly(propylene) (PP) and different levels of a premixed montmorillonite‐organoclay masterbatch (PP/clay concentrate). Melt mixing was achieved using a Gelimat, a high‐speed thermokinetic mixer. The Gelimat system is designed to handle difficult compounding and dispersion applications and can achieve mixing, heating, and compounding of products within a minute. Therefore, the thermal history of the compounded polymer is short, which limits degradation. The structure and properties of the nanocomposites prepared with a Gelimat were compared to ones prepared with a twin‐screw extruder. The structure and properties of PP/clay nanocomposites were compared by TEM, X‐ray diffraction, mechanical testing, and rheological analysis. Results indicate that a better dispersion of the clay can be achieved by thermokinetic mixing when compared to extrusion, resulting in better mechanical properties. Calculations, based on simplifying assumptions, showed that the shear rates generated in a Gelimat are at least one order higher than those generally generated in an extruder. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1557–1563, 2005

Mechanical behavior of cold plasma–treated sisal and high‐density polyethylene composites

AbstractSisal fibers and finely powdered high‐density polyethylene were surface functionalized with dichlorosilane on a RF(radio frequency)‐plasma reactor. Composites made from sisal and high‐density polyethylene were compounded using a thermokinetic mixer. The discharged mass was cooled, granulated, and injected molded into composite specimens for testing. The mechanical behaviors (tensile, impact and thermal dynamical mechanical properties) of composites made from cold plasma‐treated and untreated components are compared and discussed. The best mechanical performance was generally obtained for composites where only the inert thermoplastic matrix was plasma‐functionalized. Plasma treatment of lignocellulosic fibers seems to induce decomposition processes of the surface layers structures exposed to the plasma that generally does not contribute to significant improvement on the mechanical behavior of the composite.

Micromechanics of lignin/polypropylene composites suitable for industrial applications

Lignin/polypropylene composites were compounded by melt blending in a thermokinetic mixer and then ASTM specimens suitable for tensile testing were made by injection moulding. Two polypropylenes with different molecular weights were used as matrices. Lignin contents in the composites ranged from 10 to 55 wt.-%. Tensile modulus, strength and elongation were determined for those composites. The experimental data thus obtained were thus mathematically fitted to several micromechanical models. Micromechanical models best suited for fitting experimental data were those of Halpin-Tsai, Nielsen and Pukánszky. Fitting of predicted data to the experimental data was good in most cases, thus revealing the ability of those models for predicting the tensile properties of lignin/polypropylene composites and estimate the unknown modulus of elasticity of the lignin used as filler.

X-ray photoelectron spectroscopy of maleated polypropylene treated wood fibers in a high-intensity thermokinetic mixer

An XPS (X-ray Photoelectron Spectroscopy), also known as ESCA (Electron Spectroscopy for Chemical Analysis) study of wood fiber treated with maleated polypropylene was performed to obtain information on the chemical nature of wood fiber before and after treatment. Wood fiber was treated in a high-intensity thermokinetic mixer with maleated polypropylene at different loading level (relative to wood fiber weight). The XPS results showed that the treatment of maleated polypropylene increased the hydrocarbon concentration of wood fiber, as indicated by the decrease in oxygen-carbon ratio, and the continuous increase of the relative intensity of the component C1 in C1s signal. Based on these values, higher molecular weight maleated polypropylene produced more hydrophobic wood fiber surface than lower molecular weight maleated polypropylene. The decrease in C4 carbon type in C1s signal after treatment suggested that the esterification reaction between wood fiber and maleated polypropylene had not ocurred under the experimental conditions used in this study.

Dynamic Fracture Toughness of Cellulose-Fiber-Reinforced Polypropylene: Preliminary Investigation of Microstructural Effects

In this study, the microstructure of injection-molded polypropylene reinforced with cellulose fiber was investigated. Scanning electron microscopy of the fracture surfaces and X-ray diffraction were used to investigate fiber orientation. The polypropylene matrix was removed by solvent extraction, and the lengths of the residual fibers were optically determined. Fiber lengths were reduced by one-half when compounded in a high-intensity thermokinetic mixer and then injection molded. At low fiber contents, there is little fiber orientation; at high fiber contents, a layered structure arises. To better understand mechanisms of fracture under impact loading, dynamic fracture analysis was performed based on linear elastic fracture mechanics. Dynamic critical energy release rates and dynamic critical stress intensity factors were deduced from instrumented Charpy impact test measurements. Dynamic fracture toughness increased with cellulose content and with orientation of fibers perpendicular to the crack direction. A preliminary evaluation of a simple model relating the microstructure to the dynamic fracture toughness shows promise, but further work is needed to assess its validity.

Short jute fiber-reinforced polypropylene composites: Dynamic mechanical study

Short jute fiber-reinforced polypropylene (PP) composites were prepared using a high-speed thermokinetic mixer. A compatibilizer was used to improve the molecular interaction between jute and PP. Both the percent weight fraction of the jute fiber and compatibilizer were varied to study the dynamic mechanical thermal (DMT) properties. Dynamic parameters such as storage flexural modulus (E′), loss flexural modulus (E″), storage shear modulus (G′), loss shear modulus (G″), and loss factor or damping efficiency (tan δ) were determined in a resonant frequency mode. The transition peak nature, amplitude, and temperature of E′, E″, G′, G″, and tan δ of different compositions were shown to indicate possible improvements of molecular interaction in the presence of a compatibilizer. The modulus retention term, a plot of the reduced modulus with the weight fraction of the jute fiber, also indicate its improvement. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 531–539, 1999

Effect of Ester Linkages on the Mechanical Properties of Wood Fiber-Polypropylene Composites

The esterification reaction between several wood fibers and maleated polypropylenes, and its role in determining the mechanical properties of wood fiberpolypropylene composites was investigated. The modification technique used in this study involved bulk treatment in a thermokinetic mixer. The treatment of wood fiber with maleated polypropylene had a significant effect in increasing the mechanical properties of the composites. However, no direct evidence of ester links was detected between wood fiber and maleated polypropylene by FT-IR. Thus, the effectiveness of maleated polypropylene in improving the mechanical properties was attributed to the compatibilization effect which is accomplished by improving the wettability of wood fiber by the matrix polymer, lowering the fiber to fiber interactions, improving fibers dispersion and orientation, and enhancing the adhesion between wood fiber and polypropylene matrix.

Biofibers as reinforcing fillers in thermoplastic composites

AbstractFour biofiber materials were compared against wood flour for their ability to act as reinforcing fillers in melt‐blended composites with polypropylene as the matrix polymer. The four materials were a waste wood composite (mixture of plywood, particleboard, and fiberboard), kenaf core, a waste jute–polyester composite panel, and waste newspaper. The composites were prepared either by extrusion or by blending in a high intensity thermokinetic mixer (K‐mixer), and mechanical properties were determined on injection molded specimens. Although some property differences were observed compared to wood flour/polypropylene composites, it appeared that any of the four materials might substitute for wood flour if local supply and cost circumstances offered advantages. However, waste newspaper clearly provided the best balance of mechanical properties relative to the other three test materials or wood flour. Relative to wood flour, waste newspaper filler increased unnotched impact by over 30 percent and flexure and tensile strengths by about 25 percent.

Recycled Newspaper Fibers as Reinforcing Fillers in Thermoplastics: Part I-Analysis of Tensile and Impact Properties in Polypropylene

Recycled newspaper fibers (ONP) are potentially outstanding nonabrasive reinforcing fibers with high specific properties. In this study, a high energy thermokinetic mixer was used to mix these fibers in a polypropylene (PP) matrix, and the blends were then injection molded in order to observe the tensile and impact strengths of the compos ites. A 40% (weight) of ONP in PP resulted in a tensile strength of 34.1 MPa and an un notched Izod impact strength of 112 J/m. Small quantities of maleic anhydride-grafted polypropylene (MAPP) and acrylic acid-grafted polypropylene (AAPP) were used to im prove the interaction between the hydrophobic PP and the highly polar fibers. The im provement in properties by using MAPP depended on the amount of maleic anhydride in the graft copolymer and the molecular weight of the copolymer. Tensile strengths as high as 57 MPa and an unnotched Izod impact strength of 212 J/m were achieved with the addi tion of one of the MAPP, while smaller improvements were found with AAPP Reinforcing efficiencies and scanning electron microscopy have been utilized to aid in the analysis.

Effects of Several Ingredient Variables on Mechanical Properties of Wood Fiber-Polyolefin Composites Blended in a Thermokinetic Mixer

AbstractWe examined the influence of several variables on the mechanical properties of wood fiber-polyolefin composites blended in a thermokinetic mixer. A pure cellulose fiber and fibers from old newspaper provided similar performance in matrices of virgin polypropylene or recycled milk bottles (high density polyethylene). Relative to wood flour, these fibrous fillers led to greater strength and modulus with both plastics, to lower impact energy with polyethylene, and to similar impact energy with polypropylene. Compared with the existing commercial wood flour-polypropylene system, the totally recycled polyethylene-newspaper composite provided equivalent strength and modulus, along with greater notched impact energy. Little difference was seen in composites containing a maleated polypropylene additive in the form of the solid anhydride or the emulsified potassium salt, indicating that the additive acted as a dispersing agent and not as a strong coupling agent.