Polyamide‐6 composites reinforced with cellulose fibers and fabricated by extrusion: Effect of fiber bleaching on mechanical properties and stability

We prepared polyamide‐6 (PA‐6) composites using bleached and semibleached cellulose fibers from Eucalyptus species by processing in a corotating interpenetrating twin‐screw extruder. PA‐6 is a challenging matrix because of its high processing temperature, which overlaps the thermodegradation temperature of the fibers. The selection of the processing conditions for extrusion and the use of the lubricant ethylene bis (stearamide) permitted the production of composites with 20, 30, and 40 wt% of bleached fibers, which are lighter than the corresponding glass fiber composites. Composites with 30 wt% of bleached fibers yield the best mechanical properties and good fiber/matrix interaction, as demonstrated by mechanical tests and scanning electron microscopy. X‐ray photoelectron spectroscopy studies showed that the natural moisture in the fibers promotes the fiber/matrix interaction through the formation of ester bonds. We assessed the effect caused by the presence of lignin in the fibers. Composites containing 30 wt% of semibleached fibers maintained the flexural properties and showed small improvements in thermal stability when compared with bleached fiber composites; however, there is a slight decrease in the tensile properties. Through accelerated aging tests, we observed that increased lignin concentration in the fibers reduced the formation of carbonyl compounds on sample surfaces, indicating a stabilization effect. POLYM. COMPOS., 38:299–308, 2017. © 2015 Society of Plastics Engineers     

From polymer blends to in situ polymer/polymer composites: Morphology control and mechanical properties

In situ polymer/polymer short fiber composites were generated by a two‐step process. In the first step, a polyamide (PA) dispersed phase is blended with a polypropylene (PP) matrix in a twin‐screw extruder at a temperature at which both polymers are in molten state. The extrudate was then stretched at the die exit to generate long and thin fibers of PA in the PP matrix well oriented in the direction of flow. Adhesion between the phases was promoted by addition of PP grafted with maleic anhydride (PP‐g‐MA). During the second step, the chopped extrudates were molded by injection or compression molding at a temperature at which PA in the form of fibers is in the solid state and the PP matrix is molten. The control of the formation of such ultrafine fibers was obtained by quantitative analyses for the deformation of the minor PA‐phase during twin‐screw extrusion and stretching at the exit of the die that involve both shear and extensional flows. Morphology and mechanical properties of such polymer/polymer composites were compared to equivalent blends with dispersed spherical particles‐type morphology prepared in a batch mixer device.     

碱处理竹纤维对聚酰胺6结构和性能的影响

采用10 ％的（质量分数,下同）NaOH碱溶液对竹纤维进行了处理,通过双螺杆挤出和注射成型制备了聚酰胺6（PA6）/竹纤维复合材料。用扫描电子显微镜﹑差示扫描量热仪、X射线衍射仪和热失重分析仪等表征了材料的形貌、结构和热性能,测试了熔体流动速率和力学性能。研究表明,碱处理可清除竹纤维中的胶质物,增大其比表面积,有利于改善PA6和竹纤维间的界面结合。PA6与竹纤维之间具有较好界面结合,相界面间无明显间隙。竹纤维使复合材料中PA6晶相的完整程度降低,使复合材料刚性增加,冲击强度、熔体流动性和热稳定性下降。在挤出和注射过程中,PA6/竹纤维复合材料较好的熔体流动性和一定的热稳定性使其具有熔体加工性能。     

Reinforcement of polyamide 6 with thermotropic liquid crystalline polymer

The in-situ composites of polyamide 6 (PA 6)/liquid crystalline polymer (LCP) were investigated from the standpoint of fibrillation of LCP to develop a new high performance gear material for heavy load use that is superior to conventional plastic gears made of polyacetal (POM). LCP used was a wholly aromatic copolyester. PA 6 was chosen as the matrix polymer because of its excellent fatigue resistance. Extrusion of PA 6 added with LCP from 10 to 30 vol% was carried out at a temperature between 260 and 290°C by a twin screw extruder and take-up equipment. Insitu fibrillation of LCP droplets, which were dispersed in PA 6 matrix, took place during the process. Injection molding of the composites was followed at a temperature below the softening point of LCP fibrils so as to keep the fibrils as extruded. Key factors for fibrillation of LCP were found as follows: (1) control of stress relaxation of LCP when the melt passes through the die-head, (2) the optimum temperature of nent, (3) the optimum LCP content, and (4) addition of a small amount of 3rd component. A gear made of in-situ composite of PA 6/LCP (30 vol%) added with 2-functional epoxy resin (2.5 phr) was found to bear a load about 1.2 times heavier than a POM gear.     

Thermal and flow property–morphology relationship of sugarcane bagasse fiber‐filled polyamide 6 blends

The structure–property relationship of sugarcane bagasse fiber‐filled polyamide 6 blends at different blend compositions has been investigated. Blends were prepared in the composition of wt % PA6/wt % bagasse as follows: 98/2, 95/5, and 90/10 for three fiber length ranges (<100, <250, and <500 μm) using a twin‐screw extruder. Thermal properties were evaluated by measuring the glass transition temperature T_g, enthalpy of fusion ΔH_f, crystallinity X_c and thermogravimetry, TG. Results showed that T_g of the composites changed with change in fiber loading and length. The X_c as well as ΔH_f of the blends reduced to almost half its value for the neat PA6. The thermogravimetric curves TG showed that the thermal stability of the composites was lower than that of the neat PA6. Rheological properties were studied as a function of fiber loading, fiber length, shear rate, and temperature. The viscosity of composites increased with increasing fiber loading and length at low shear rates but decreased below that of neat PA6 at high shear rates. It was also found to be temperature sensitive, and influenced by fiber lengths particularly at higher temperatures. The morphology of the blends was studied using a Leica laser scanning confocal microscopy at two different regions: at the wall, and the core. The micrographs of the blends showed that fibers present in the form of bundles were found at the wall of the extrudates and increased in volume with increase in both length and concentration, at the same temperature and shear stress. In the core region, there is laminar flow, presenting striation morphology, with the omnipresent bundles of fibers dispersed in the matrix. At higher shear rates, the bundles were pushed to the wall. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3744–3754, 2004     

Investigation of rheology and morphology to follow physical fibrillar network evolution through fiber spinning of PP/PA6 blend fiber

This work is aimed at investigating the influence of fibrillar morphology of deformed Polyamide 6 (PA6) droplets dispersed in Polypropylene (PP) matrix on the melt viscoelastic behavior of their blends. The blends of PP with various amounts of PA6 (1%, 6%, 10%, and 20%) were prepared by melt mixing in a co‐rotating twin screw extruder and fibrillated by fiber spinning process. Scanning Electron Microscopy revealed that the PA6 spherical droplets form fibrillar inclusions after fiber spinning. The steady and transient shear rheological responses of samples were evaluated in both linear and nonlinear ranges of deformation. Non‐terminal behavior of storage modulus at low frequency appeared as a typical characteristic of fibrillar morphology whose width and value depend on fibril growth. Storage modulus and complex viscosity of the blends containing PA6 fibrillated structure were remarkably enhanced compared to as‐extruded samples. The fibrillar‐induced elasticity of the fibers is a distinguishable behavior which was revealed by conducting transient stress and creep‐recovery measurements and upon appearing mature fibrils, elasticity of the polymer blend fibers increased significantly. POLYM. ENG. SCI., 58:1251–1260, 2018. © 2017 Society of Plastics Engineers     

In-situ generation of polyamide-6 fibrils in polypropylene processed with a single screw extruder

Polypropylene(PP) and polyamide6(PA6) were extruded with a single screw extruder. It was found that when PA6 was in the dispersed phase, it could deform and fibrillate in the PP matrix in the shear force field generated by the rotating screw. Dynamic mechanical analysis and mechanical tests showed that the mechanical properties, such as the tensile strength, impact strength, and modulus, were different in the different processing directions. With the addition of PP-g-MAH as a compatibilzer, the number of fibrils decreased and the dimension of the dispersed phase decreased significantly. This indicated that the compatibility has a strong effect on the in-situ fibrillation.     

Properties of talc/wollastonite/polyamide 6 hybrid composites

In this study, it was aimed to investigate the mechanical, thermal, and morphological properties of PA6 hybrid composites containing talc and wollastonite. Talc and wollastonite filled single and hybrid composites were prepared with melt compounding in a twin screw extruder. The filler content was 40% by weight and the wollastonite/talc ratio was 40/0, 30/10, 20/20, 10/30, and 40/0. The melt flow rate measurements showed that incorporation of fillers into the polyamide 6 (PA6) resulted in an increment in melt viscosity of composites. The presence of a homogeneous dispersion of fillers in the matrix was obtained from morphological analysis. It was revealed from the mechanical tests that in most cases, mechanical properties of 20/20 hybrid composites were significantly higher than that of the single and the other hybrid composites. Heat deflection temperature of the composite was markedly improved by the addition of fillers. Differential scanning calorimeter analysis showed that talc and wollastonite acted as a nucleating agent for PA6. POLYM. COMPOS., 36:739–746, 2015. © 2014 Society of Plastics Engineers     

PA 6原位成纤复合改善PP的力学性能

采用挤出-热拉伸-淬冷法制备均聚聚丙烯(PP-H)/聚酰胺(PA)6原位成纤复合材料,研究PA 6的原位微纤化对PP-H力学性能的影响。结果表明:实验设计工艺可实现PA 6在PP-H基体中的原位微纤化,纤维直径约为0.5～2.0μm,但PA 6微纤与PP-H基体的界面结合性差,对PP-H的力学性能改善不佳;添加少量增容剂马来酸酐接枝聚丙烯,可显著改善PP-H的力学性能,当w(PA 6)为15%时,添加少量增容剂后,复合材料的拉伸强度、弯曲强度、简支梁缺口冲击强度分别为未添加增容剂时的1.27,1.39,1.49倍;注塑温度对复合材料中PA 6分散相的形态及材料力学性能有明显影响,高温注塑试样的力学性能普遍低于低温注塑试样。     

Improvement of adhesion between polyethylene and regenerated cellulose fibers by surface fibrillation

Regenerated cellulose fibers spun from straw pulp using the N-methylmorpholine N-oxide (NMMO) process were evaluated as a reinforcement for low-density polyethylene (LDPE). Surface fibrillation was carried out by a mechanical treatment to improve interfacial adhesion. Surface fibrillation resulted in a gradual change in surface topography, as detected by SEM. Long and numerous twisted fibrils were observed on the surface of the treated fibers. The fiber perimeters, determined by the Wilhelmy plate method, increased with an extended degree of fibrillation, while the strength of the fiber was not affected by the surface treatment. Model composites were prepared by embedding untreated and surface-fibrillated single fibers into an LDPE matrix, and the single fiber fragmentation (SEF) test was carried out to determine the critical fiber length. The interfacial shear strength (τ) was then calculated by applying a modified form of the Kelly-Tyson equation. It was found that the interfacial shear strength increased significantly as a result of surface fibrillation. The proposed mechanism for the improvement of interfacial adhesion is a mechanical anchoring between the matrix and the fiber.     

Short glass fiber reinforced ABS and ABS/PA6 composites: Processing and characterization

In this study acrylonitrile‐butadiene‐styrene (ABS) terpolymer was reinforced with 3‐aminopropyltrimethoxysilane (APS)‐treated short glass fibers (SGFs). The effects of SGF concentration and extrusion process conditions, such as the screw speed and barrel temperature profile, on the mechanical properties of the composites were examined. Increasing the SGF concentration in the ABS matrix from 10 wt% to 30 wt% resulted in improved tensile strength, tensile modulus and flexural modulus, but drastically lowered the strain‐at‐break and the impact strength. The average fiber length decreased when the concentration of glass fibers increased. The increase in screw speed decreased the average fiber length, and therefore the tensile strength, tensile modulus, flexural modulus, and impact strength were affected negatively and the strain‐at‐break was affected positively. The increase in extrusion temperature decreased the fiber length degradation, and therefore the tensile strength, tensile modulus, flexural modulus, and impact strength increased. At higher temperatures the ABS matrix degraded and the mechanical strength of the composites decreased. To obtain a strong interaction at the interface, polyamide‐6 (PA6) at varying concentrations was introduced into the ABS/30 wt% SGF composite. The incorporation and increasing amount of PA6 in the composites broadened the fiber length distribution (FLD) owing to the low melt viscosity of PA6. Tensile strength, tensile modulus, flexural modulus, and impact strength values increased with an increase in the PA6 content of the ABS/PA6/SGF systems due to the improved adhesion at the interface, which was confirmed by the ratio of tensile strength to flexural strength as an adhesion parameter. These results were also supported by scanning electron micrographs of the ABS/PA6/SGF composites, which exhibited an improved adhesion between the SGFs and the ABS/PA6 matrix. POLYM. COMPOS. 26:745–755, 2005. © 2005 Society of Plastics Engineers     

Effects of Malienated Ethylene Propylene Diene Monomer (EPDM) Rubber on Dynamic-Mechanical and Rheological Properties of Polyamide 66 (PA 66) Composites

Reactive blends of ethylene propylene diene monomer (EPDM) and polyamide (PA) 66 were prepared in the single screw and twin screw extruder using maleic anhydride as coupling agent and dicumyl peroxide (DCP) as initiator. The optimum concentration of DCP for grafting maleic anhydride on EPDM was determined. The grafting efficiency was determined by Fourier transform infrared (FTIR) spectroscopy, and (DMTA) tests were conducted to determine the damping, loss, and storage modulus of PA 66 composites. A capillary rheometer and parallel plate rheometer were employed to characterize the rheological properties at high and low shear rates. It was seen that the glass fibers are not long and continuous, and they act as fillers, therefore reducing the damping in the composite. No significant change was observed in the glass transition temperature of the blend as compared with the individual components, especially PA 66. In malienated EPDM blends with increasing EPDM from 10 to 15%, the height of glass transition temperature peak increases. Capillary rheometer tests show that for all samples the apparent viscosity decreases with increasing shear rate, which is a characteristic of a non-Newtonian pseudo plastic fluid. The viscosity ration of malienated EPDM and PA 66 shows a considerable difference between them and only at higher shear rates do the viscosities get closer.     

高含量玻璃纤维增强阻燃聚酰胺材料的制备与性能

采用双螺杆挤出机制备了聚酰胺6(PA6)/50%（质量分数,下同）玻璃纤维（GF）、PA66/50%GF、PA56/50%GF 3种高含量GF增强阻燃PA复合材料,对比研究了红磷、溴系、磷氮3种阻燃体系下复合材料的力学性能、阻燃性能和激光打标性能。结果表明,不同阻燃体系对复合材料的力学性能有明显影响,吸水平衡后,PA66复合材料的力学性能保持率最高;PA56复合材料在3种阻燃体系中均表现出比PA6、PA66复合材料更好的阻燃性能;红外激光和紫外激光的打标效果存在明显不同,而在阻燃体系和激光光源相同的条件下,PA6、PA66和PA56 3种PA复合材料的激光打标效果没有明显差异。     

Morphology and Osteogenetic Characteristics of Polyamide/ NanoHydroxyapatite Biocomposites

Summary  The effect of shear or time of shearing – as exerted by different screw configurations – upon the nano hydroxyapatite (n-HA) dispersion, during the twin screw extrusion processing for the preparation of PA6-66/n-HA composites, was investigated. Three different screw configurations, designated as medium, high and very high shear, were used. A noticeable improvement in the n-HA dispersion, attributed to the increasing shear exerted upon the melt during mixing in the TSE, was observed. Crystallization and thermal behavior of n-HA reinforced PA6-66 composites were studied by X-Ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). An increase in the crystallization temperature, accompanied by a decrease in percent crystallinity with the addition of n-HA to the PA6-66 matrix was observed. That is, n-HA acted as a nucleating agent and enhanced the crystallization rate. In addition, it was observed that the n-HA promoted the occurrence of the Brill transition. The decomposition temperature increased with the addition of n-HA. The PA6-66/ n-HA nanocomposite was thereafter, immersed in simulated body fluid (SBF) and the generation of a new calcium phosphate layer on the nanocomposite surface was monitored by SEM, FTIR and Atomic Absorption. The Ca/P ratio in the forming apatite layer started at a low value, ca. 1.3, which corresponds to octacalcic phosphate, but increased with the immersion time to 1.6, which corresponds to carbonated apatite.     

Preparation,structure, and properties of the PTT/SGF composites

Short glass fiber reinforced poly(trimethylene terephthalate) composites (PTT/SGF) were prepared by twin screw extruder. The structural feature and physical properties of these composites were studied by scanning electron microscope, differential scanning calorimetry, thermalgravimetric analyzer, capillary rheometer, universal tester, etc. The glass fiber was modified by the silane coupling agent before being blended with the polymer. The results suggest that there is strong interaction between SGF and PTT matrix, which leads to an increasing on the tensile strength, Young's modulus, impact strength and thermal stability of the composites with proper contents of SGF. Rheological behavior of the PTT/SGF composites melt is complicated, combining a dilate fluid at lower shear rate and a pseudo-plastic fluid at higher shear rate. The melt apparent viscosity of composites decreases with increasing SGF content because of the rigid fibers improving the flow of the melt. Moreover, the flow activation energy of the composites suggests that the melt with more SGF has lower sensitivity to the processing temperature. In conclusion, the composite with 10–20 wt% content of SGF has better properties. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Effect of the preparation of cellulose pellets on the dispersion of cellulose fibers into polypropylene matrix during extrusion

Cellulose fibers are rarely used for the extrusion of composites because of the problems in feeding them into the extruder and in dispersing them properly. Pelletization made it possible to feed cellulose fibers into extruder, but it reduced dramatically the fiber length. The goal of this study was to optimize the pelletization process for extrusion applications. Bleached sulfite cellulose fibers were pelletized at different moisture contents and with the optional addition of carboxymethyl cellulose (CMC). The pellets were subsequently extruded with polypropylene matrix without compatibilizer. Fiber dispersion and fiber breakage during extrusion were investigated. Pre‐blending of polymer and fiber pellets and introduction of the fibers through a side extruder were compared. CMC acted as a processing aid during pelletization, resulting in lower fiber breakage but in compact and stiff pellets. Lower moisture content also increased the compactness of the pellets. The dispersability of the fibers during extrusion decreased with increased pellets' compactness. CMC created inter‐fiber bonds, decreasing further the fibers' dispersability. The fiber length in the composites was the same regardless of the pelletization parameters. Early introduction of the fibers improved fiber dispersion. Feeding through side extruder was more stable and more reliable than pre‐blending. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

工艺条件对沥青炭纤维/ABS树脂复合材料导电性及力学性能的影响

研究了单螺杆挤出机挤出温度及螺杆转速对沥青炭纤维填充ＡＢＳ树脂复合材料导电性及力学性能的影响。结果表明,纤维经挤出后,纤维长度有不同程度的降低,长径比减小,随着挤出的升高及螺杆转速的降低,纤维长径比增大,挤出条件对复合材料电性能及力学性能的影响主要可归结为长径比对材料的影响,随着长径比增加,复合材料的导电性及拉伸强度均有增大。此外,复合材料导电性及拉伸强度随复合材料中纤维填加量的增多而增大。     

Effects of preferential encapsulation of glass fiber on the properties of ternary GF/PA/PP blends

Long fiber molding materials are expected to play an important role in the near future. This paper describes a series of experiments performed to examine properties of ternary blends containing glass fiber (GF), polyamide (PA), and polypropylene (PP). The continuous glass fiber was impregnated with one of the blend constituent polymers by our specially designed impregnation apparatus and cut into chips of 6 mm length. These chips and the other polymer were used to produce various testing specimens in a twin screw extruder or in injection molding machine. The results indicated that the effect of fiber addition on the mechanical and rheological properties is clearly dependent on the order of impregnation process. In the blends containing the GF/PA + PP, the GFs are preferentially encapsulated with PA, and therefore the mechanical properties are superior to the blends with the GF/PP + PA in which the PP phase is located surrounding the GFs. This improved wetting of fibers by sequential impregnation not only resulted in better properties but also protected the fibers from shear action of the screw, thereby allowing significant increase in average fiber length to be achieved in the injection molding process.     

Friction and wear properties of PTFE composites filled with PA6

Blending Polytetrafluoroethylene (PTFE) to PA6 at different compositions was produced in a corotating twin‐screw extruder, where PTFE acts as the polymer matrix and PA6 as the dispersed phase. The effects of PA6 content on the tribological properties of the composites were investigated. The worn surface morphologies of neat PTFE and its composites were examined by scanning electron microscopy (SEM), and the wear mechanisms were discussed. The presence of PA6 particles dispersed in the PTFE continuous phase exhibited superior tribological characteristics to unfilled PTFE. The optimum wear reduction was obtained when the content of PA6 is 30 vol%. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Effects of polyamide 6 incorporation to the short glass fiber reinforced ABS composites: an interfacial approach

The properties of 30 wt% short glass fiber (SGF) reinforced acrylonitrile-butadiene-styrene (ABS) terpolymer and polyamide 6 (PA6) blends prepared with extrusion were studied using the interfacial adhesion approach. Work of adhesion and interlaminar shear strength values were calculated respectively from experimentally determined interfacial tensions and short beam flexural tests. The adhesion capacities of glass fibers with different surface treatments of organosilanes were evaluated. Among the different silanes tested, γ-aminopropyltrimethoxysilane (APS) was found to be the best coupling agent for the glass fibers, possibly, because of its chemical compatibility with PA6. Tensile test results indicated that increasing amount of PA6 in the polymer matrix improved the strength and stiffness of the composites due to a strong acid–base interaction at the interface. Incorporation of PA6 to the SGF reinforced ABS reduced the melt viscosity, broadened the fiber length distributions and increased the toughness of the composites. Fractographic analysis showed that the incorporation of PA6 enhanced the interactions between glass fibers and the polymeric matrix.