Reactive melt blending of PS‐POSS hybrid nanocomposites

Hybrid nanocomposites of polystyrene (PS) and methacryl phenyl polyhedral oligomeric silsesquioxane (POSS) were synthesized by reactive melt blending in the mixing chamber of a torque rheometer using dicumyl peroxide (DCP) as a free radical initiator and styrene monomer as a chain transfer agent. The effects of mixing intensity and composition on the molecular structure and morphology of the PS‐POSS hybrid nanocomposites were investigated. The degree of POSS hybridization (α_POSS) was found to increase with the POSS content, DCP/POSS ratio, and rotor speed. For the PS‐POSS materials processed in the absence of styrene monomer, an increase in the α_POSS led to a reduction in the molecular weight by PS chain scission, as a consequence of the free radical initiation. On the other hand, the use of styrene monomer as a chain transfer agent reduces the steric hindrance in the hybridization reaction between POSS and PS, enhancing the degree of POSS hybridization and avoiding PS degradation. The PS‐POSS morphology consists of nanoscale POSS clusters and particles and microscale crystalline POSS aggregates. PS‐POSS with higher α_POSS values and lower amounts of nonbound POSS showed improved POSS dispersion, characterized by smaller interfacial thickness (t) and greater Porod inhomogeneity lengths (l_p). The processing‐molecular structure–morphology correlations analyzed in this study allow the POSS dispersion level in the PS‐POSS materials to be tuned by controlling the reactive melt blending through the choice of the processing conditions. These insights are very useful for the development of PS‐POSS materials with optimized performance. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Improved mechanical properties of organoclay/nylon 6 nanocomposites prepared via a supercritical carbon dioxide‐aided,melt blending method

The use of supercritical carbon dioxide (scCO₂) as a processing aid to help exfoliate nanoclays and improve their dispersion after melt blending in polymer matrices has been reported in the literature by our laboratory and others. Previous work has focused on nonpolar polymers such as polypropylene. In this work, the supercritical carbon dioxide‐aided, melt blending method with single‐screw compounding was applied to an organoclay/nylon 6 composite system with favorable interactions. Wide‐angle X‐ray diffraction, transmission electron microscopy, dynamic mechanical testing, and tensile tests are provided to investigate the effect of processing with scCO₂ on the final composite morphology and properties. It was found that properties of composites prepared with the scCO₂‐aided method were similar to or higher than those reported in the literature for samples prepared with twin‐screw compounding. At 7.6 wt% the modulus value reached 4.75 GPa which is one of the highest increases (1.7 GPa) reported for these materials processed at intermediate concentrations. Beyond 7.6 wt% the improvement due to scCO₂ processing matches that of direct blending. It is possible that with the use of a twin‐screw extruder, the modulus would continue to increase. The use of nylon illustrates the importance of having functionalities that can interact with the clay during scCO₂‐aided melt compounding. POLYM. COMPOS. 36:527–537, 2015. © 2014 Society of Plastics Engineers     

Mechanical and structural properties of melt spun polypropylene/nylon 6 alloy filaments

Investigated in the present study are the physical properties, morphology, and structure of PP/N6 alloy filaments (10, 20 wt % N6) made with or without PP‐g‐MAH as compatibilizer. The alloy filaments produced at the take‐up speeds of 300 and 800 m/min were drawn with draw ratio of 3.5 and 2, respectively. Stress–strain curves of PP and alloy filaments show ductile and brittle behavior, respectively. It is suggested that the brittle behavior of alloy filaments is due to the presence of microvoids or micropores at the interface of PP and N6; these lead to stress concentration and thus to a decrease in tenacity, modulus, and elongation at break. Effects of the blending of N6 with PP on birefringence and crystalline and amorphous orientation factors of the composite filaments are studied. The amorphous orientation factor, f_am, of PP was found to increase with an increase in the amount of N6. The alloy filaments behaved like isostrain materials and most of the force in spinning and drawing was born by the PP phase. The presence of N6 fibrils helped to orient PP chain molecules in amorphous regions. However, the crystalline factor, f_c, of PP decreased with the increase in nylon fraction. This means the presence of the crystals of N6 caused a decrease in the orientation of the PP crystals. LSCM micrographs of the filament showed the presence of matrix–fibril morphology with the N6 fibrils oriented along the axis. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 532–544, 2005     

Morphology and mechanical properties of polypropylene‐POSS hybrid nanocomposites obtained by reactive blending

The polypropylene‐polyhedral oligomeric silsesquioxane (PP‐POSS) organic–inorganic hybrids were obtained and studied. The hybrids were prepared by grafting of POSS on PP chains during a reactive melt‐blending of polypropylene (iPP), maleic anhydride functionalized PP (PP‐g‐MA), and amine‐functionalized POSS (aminopropylheptaisobutyl‐POSS, ambPOSS, aminopropylheptaisooctyl‐POSS, amoPOSS, or aminoethylaminopropylheptaisobutyl‐POSS, am2bPOSS), taking advantage of the high efficiency of amino‐anhydride reaction in the molten state. The structure, morphology, and physical properties of the obtained hybrids and blends were studied by means of wide‐ and small‐angle X‐ray scattering, dynamic scanning calorimetry, scanning electron microscopy, dynamic mechanical thermal analysis, as well as tensile and impact experiments. The influence of POSS chemical structure and grafting degree on the morphological characteristics and mechanical properties was investigated. It was found that grafting of POSS cages on PP chains leads to the POSS dispersion on the molecular level. On contrary, when POSS was mixed with plain iPP any grafting of POSS on iPP chains was impossible, which resulted in phase‐separated blend with crystallites of POSS dispersed in iPP matrix. The mechanical tests revealed that modification of polypropylene by grafting with POSS molecules does not affect significantly its mechanical properties, both static and dynamic, except ultimate strain, which is markedly lower in hybrids and their blends than in plain iPP. Also the impact properties of PP were practically not improved by modification with POSS. POLYM. COMPOS., 34:929–941, 2013. © 2013 Society of Plastics Engineers     

Structural evolution and mechanical properties of iPP melt spun fibers subjected to thermal treatment

An investigation of the structure and mechanical behavior of melt-spun isotactic polypropylene (iPP) fibers subjected to thermal treatment in an inert atmosphere is described. Two iPP formulations, Basell Pro-fax PH835 and ExxonMobil Achieve 3854, synthesized by the Ziegler-Natta and metallocene catalysts respectively, and spun at take-up velocities of 1000 to 3000 m/min are considered. The evolution of the structure is monitored with WAXS, SAXS, Raman spectroscopy and birefringence measurements. The fibers spun at 1000 m/min are predominantly mesomorphic, while those spun at 3000 m/min are semi-crystalline in the as-spun state. Thermal treatment for 20 min at 145 °C erases the processing history and increases the crystallinity of all samples. It is shown that thermal treatment leads to the formation of a secondary set of kebab lamellae which are thinner than the original ones, separated by thicker lamellae. The spatial variability of the lamellar thickness and of interlamellar spacings is estimated from the SAXS data and it is concluded that the variability is rather pronounced in all samples. Both annealed and non-annealed fibers are subjected to monotonic and cyclic mechanical testing. Large differences are seen in the behavior of non-annealed fibers processed in different conditions. The monotonic mechanical behavior of the annealed fibers is not very much different from that of the corresponding non-annealed fibers. The central difference between annealed and non-annealed samples is observed in the cyclic behavior; annealed samples containing lamellae with bimodal distribution of thickness exhibit bimodal hysteresis curves while this feature is not observed in non-annealed samples.     

Structure and properties of polyimide‐g‐nylon 6 and nylon 6‐b‐polyimide‐b‐nylon 6 copolymers

Polyimide‐g‐nylon 6 copolymers were prepared by the polymerization of phenyl 3,5‐diaminobenzoate with several diamines and dianhydrides with a one‐step method. The polyimides containing pendant ester moieties were then used as activators for the anionic polymerization of molten ε‐caprolactam. Nylon 6‐b‐polyimide‐b‐nylon 6 copolymers were prepared by the use of phenyl 4‐aminobenzoate as an end‐capping agent in the preparation of a series of imide oligomers. The oligomers were then used to activate the anionic polymerization of ε‐caprolactam. In both the graft and copolymer syntheses, the phenyl ester groups reacted quickly with caprolactam anions at 120°C to generate N‐acyllactam moieties, which activated the anionic polymerization. All the block copolymers had higher moduli and tensile strengths than those of nylon 6. However, their elongations at break were much lower. The graft copolymers based on 2,2′‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride and 2,2′‐bis[4‐(4‐aminophenoxy)phenyl]propane displayed elongations comparable to that of nylon 6 and the highest moduli and tensile strengths of all the copolymers. The thermal stability, moisture resistance, and impact strength were dramatically increased by the incorporation of only 5 wt % polyimide into both the graft and block copolymers. The graft and block copolymers also exhibited improved melt processability. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 300–308, 2006     

Enhancing mechanical properties of gel‐spun polyvinyl alcohol fibers by iodine doping

High strength polyvinyl alcohol (PVA) fibers with a conventional degree of polymerization of 1500 were prepared by doping iodine with PVA spinning solution. The iodine‐doped PVA (I‐PVA) aqueous solution was extruded into cold methanol that provides dark purple PVA‐iodine complex gel fibers. Only a small amount of iodine was required to enhance drawability and molecular orientation by reducing the interaction between PVA chains. An increase of ca. 10% in the maximum draw ratio of the doped fibers compared with that of undoped PVA translated into values for the tensile strength, 2.2 Giga‐Pascal (GPa), and initial modulus (47 GPa) that were more than 30% higher than those of the neat PVA fiber. Easier chain slippage of molecules in the amorphous segments of the I‐PVA fiber during drawing leads to increased orientation in these segments, which is believed to be the source of the improvements in mechanical properties. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Higher-order structures and mechanical properties of stereocomplex-type poly(lactic acid) melt spun fibers

Equimolar blend of poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) was melt spun into fibers and the relations among the processing conditions, crystalline structures, thermal properties, and mechanical properties were investigated. Drawing and annealing were performed in order to obtain fiber mainly consisting of the stereocomplex crystal phase. Fibers drawn at various temperatures exhibited either amorphous, highly oriented homo crystal, or the mixture of homo and stereocomplex with a fairly low orientation depending on the drawing temperature. Annealing of the drawn fibers at an elevated temperature higher than the melting temperature of homo crystal increased the stereocomplex content significantly. The fractions of the homo and the stereocomplex crystals strongly depended on the higher-order structure of the drawn fibers and the annealing temperature.     

Morphology and crystallization behavior of nylon 6‐clay/neat nylon 6 bicomponent nanocomposite fibers

Nylon 6‐clay hybrid/neat nylon 6, sheath/core bicomponent nanocomposite fibers containing 4 wt % of clay in sheath section, were melt spun at different take‐up speeds. Their molecular orientation and crystalline structure were compared to those of neat nylon 6 fibers. Moreover, the morphology of the bicomponent fibers and dispersion of clay within the fibers were analyzed using scanning electron microscopy and transmission electron microscopy (TEM), respectively. Birefringence measurements showed that the orientation development in sheath part was reasonably high while core part showed negligibly low birefringence. Results of differential scanning calorimetry showed that crystallinity of bicomponent fibers was lower than that of neat nylon 6 fibers. The peaks of γ‐crystalline form were observed in the wide‐angle X‐ray diffraction of bicomponent and neat nylon 6 fibers in the whole take‐up speed, while α‐crystalline form started to appear at high speeds in bicomponent fibers. TEM micrographs revealed that the clay platelets were individually and evenly dispersed in the nylon 6 matrix. The neat nylon 6 fibers had a smooth surface while striped pattern was observed on the surface of bicomponent fibers containing clay. This was speculated to be due to thermal shrinkage of the core part after solidification of the sheath part in the spin‐line. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39996.     

Morphology and mechanical properties of high density polyethylene‐POSS hybrid nanocomposites obtained by reactive blending

The high density polyethylene‐polyhedral oligomeric silsesquioxane (HDPE‐POSS) organic–inorganic hybrids were obtained and their properties studied. The hybrids were prepared by grafting of POSS on polyethylene chains during reactive melt‐blending of HDPE, maleic anhydride functionalized HDPE and amine‐functionalized POSS, taking advantage of the high efficiency of amine‐anhydride reaction in the molten state. The structure, morphology, and physical properties of the obtained hybrids and blends were studied to find the influence of POSS chemical structure and grafting degree on the morphological characteristics and mechanical properties of hybrid nanocomposites. It was found that grafting of POSS cages on HDPE chains leads to the POSS dispersion at the molecular level. On the contrary, when POSS was mixed with plain HDPE any grafting of POSS on polyethylene chains was not possible, which resulted in phase‐separated blend. The mechanical tests revealed that modification of polyethylene by grafting with POSS molecules does not affect significantly its mechanical properties, both static and dynamic, except ultimate strain, which is lower in hybrids and their blends than in plain HDPE. The impact properties (Izod impact strength) were slightly improved by grafting of HDPE with POSS. HDPE‐g‐POSS hybrids demonstrated also much enhanced thermo‐oxidative stability comparing to plain polyethylene. POLYM. ENG. SCI., 55:2058–2072, 2015. © 2014 Society of Plastics Engineers     

Enhanced mechanical properties of multilayer nano‐coated electrospun nylon 6 fibers via a layer‐by‐layer self‐assembly

We reported the mechanical properties of the polyelectrolyte multilayer nano‐coated electrospun fiber mats with different number of layers. Multilayer nano‐coatings composed of layers of PSS and PAH were successfully deposited onto electrospun nylon 6 fibers via layer‐by‐layer self‐assembly. Compared with pure nylon 6 fibers, the morphology of polyelectrolyte multilayer coated nylon 6 fibers was uniform and smooth. The mechanical properties of polyelectrolyte multilayer coated random and aligned nylon 6 fibers were remarkably enhanced. Moreover, it was found that the higher degree of alignment resulted in higher tensile strength, suggesting the combined effects of the alignment, the surface nanocoating and the formation of internal networks of polyelectrolytes on nylone 6 fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of superfine silk protein powders on mechanical properties of wet‐spun polyurethane fibers

Mechanical measurements were employed to investigate the effects of three types of superfine silk protein powder on tensile strength, elongation, and elasticity of wet‐spun Pellethane^® 2363‐80AE polyurethane (PU) fiber. These superfine silk protein powders included undegummed silk (with both native silk fibroin and sericin, water insoluble), native silk fibroin (with native silk fibroin only, water insoluble), and regenerated silk fibroin (with regenerated silk fibroin only, water soluble) in powder form. Experimental data derived from the mechanical measurements illustrated that the miscibility between the PU and regenerated silk fibroin were superior to that between PU and the other two silk proteins. This may be attributed to the similar chemical structure and microphase separation of PU and regenerated silk fibroin with lower molecular weight than native silk fibroin. This preliminary work may provide some information for biomimetic processing of silk‐inspired PU biofibers, which combine elasticity of synthetic PU with biofunction of natural silk fibroin for special biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

熔融纺酚醛纤维快速交联固化工艺研究

以热塑性酚醛树脂为原料,采用熔融纺丝法制备酚醛初生纤维;将酚醛初生纤维浸入盐酸-甲醛交联浴中,常温下预处理一定时间,然后快速加热升温使之交联,制得溶液快速交联酚醛纤维;再将溶液快速交联酚醛纤维在一定温度下进行热处理2 h,得到快速交联固化酚醛纤维。探讨了酚醛纤维的快速交联固化工艺,研究了酚醛纤维的结构与性能并与常规盐酸-甲醛交联浴固化法制得的酚醛纤维(简称常规固化酚醛纤维)进行对比。结果表明:酚醛初生纤维浸入盐酸-甲醛交联浴中,其盐酸质量分数为16%,预处理时间为48 h时,制得的溶液快速交联酚醛纤维的断裂强度为0.84 cN/dtex;溶液快速交联酚醛纤维在热处理温度200℃时,纤维断裂强度达到最大值为1.10 cN/dtex;快速交联固化酚醛纤维与常规固化酚醛纤维在失重率为5%,10%,20%时的温度相当,二者相差约3℃,二者在900℃时的质量保持率分别为63.8%,64.1%;快速交联固化酚醛纤维表面光滑,无褶皱、收缩,断面呈韧性断裂,并未出现皮芯结构;采用快速固化工艺制备的快速交联固化酚醛纤维可以达到常规固化酚醛纤维的固化效果。     

Thermal properties of photo-oxidized nylon 6 fibers

Nylon 6 fiber begins to increase in weight at about 180°C when heated in oxygen. The increase is attributed to an uptake of oxygen resulting from thermal oxidation. A similar weight increase is not found in photo-oxidized nylon 6 on heating in oxygen. It appears that nylon 6 tends to form volatile compounds more easily on heating after photodegradation. Changes detected by differential thermal analysis and also by thermomechanical analysis after nylon 6 has been exposed to sunlight are discussed primarily in terms of the supramolecular structure of the fiber.     

Effect of melt temperature and skin‐core morphology on the mechanical performance of nylon 6

The crystalline texture and mechanical (tensile and flexural) properties of injection molded nylon 6 were evaluated to understand the influence of the melt temperature (T_mlt), one of the key‐processing variables. The mechanical properties are found to be sensitive to T_mlt only below ～ 250°C. Rapid quenching of the surface produces a skin with lower crystallinity than the core, which cools more slowly; because of this difference in the rate of cooling, the crystalline component in the skin is rich in γ and that in the core is rich in α. The thickness of this skin decreases from about 1.25 mm to 0.75 mm as T_mlt increases from 225°C to 310°C. Higher tensile strength at yield, lower elongation at break and higher flexural strength were observed in specimens molded at lower T_mlt. These characteristics are associated with thicker and less ordered skin, and a lower crystallinity core. The role of the T_mlt, on microstructure and mechanical properties of injection molded nylon 6, the development of skin‐core morphology, and the role of the residual stresses in the core are discussed.     

Structural studies of electrospun nylon 6 fibers from solution and melt

Nylon 6 (N6) fibers have been fabricated via two different electrospinning schemes, from solution of N6 and formic acid at room temperature as well as from N6 melt at elevated temperature. The crystal structures of electrospun N6 fibers from solution and melt, and the annealing effect on the structures were studied by using various techniques. Combined analysis of the differential scanning calorimetry (DSC) at various heating rates, temperature-dependent X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy indicates that N6 fibers from melt predominantly exhibit the meta-stable γ-crystalline forms and low molecular orientation, while solution electrospun fibers from slowly evaporating solvent show both α- and γ-form crystals and higher degree of molecular orientation. At high annealing temperature, the meta-stable γ-crystals in melt electrospun fibers easily transform into thermodynamically stable α-form crystals, while crystals in solution electrospun fibers exhibit higher thermal stability. Nonisothermal modeling and in-situ measurements of jet temperature indicate that rapid quenching due to enhanced heat transfer by electrohydrodynamically driven air flow near the jet is responsible for the less stable γ-crystals and lower degree of molecular orientation in melt electrospun fibers.     

熔纺聚乳酸纤维的结构与性能研究

通过熔融纺丝法制备了生物可降解左旋聚乳酸(PLLA)纤维,对纤维进行了拉伸和热定型等后处理,用电子单纤维强力仪和X-射线衍射仪研究了PLLA纤维的力学性能和结晶性能,讨论了纺丝温度、拉伸倍数、定型时间和定型温度等对纤维力学性能的影响。结果表明,当纺丝温度为200℃时,纤维可纺性最好。当拉伸倍数为4倍,热定型温度为60℃,定型时间为30min时,PLLA纤维具有最佳的力学性能,其晶区具有α晶型结构。     

Structure development in the melt spinning of nylon 66 fibers and comparison to nylon 6

The development of crystallinity and orientation during the melt spinning of nylon 66 was investigated. Nylon 66 was found to crystallize in the spinline to form the Bunn-Garner α-triclinic structure. This behavior differs from that of nylon 6. Nylon 66 was found to develop lower crystalline orientation than nylon 6 under comparable spinning conditions.     

Solid‐state mechanical properties of polypropylene/nylon 6/clay nanocomposites

The mechanical and thermomechanical properties as well as microstructures of polypropylene/nylon 6/clay nanocomposites prepared by varying the loading of PP‐MA compatibilizer and organoclay (OMMT) were investigated. The compatibilizer PP‐MA was used to improve the adhesion between the phases of polymers and the dispersion of OMMT in polymer matrix. Improvement of interfacial adhesion between the PP and PA6 phases occurred after the addition of PP‐MA as confirmed by SEM micrographs. Moreover, as shown by the DSC thermograms and XRD results, the degree of crystallinity of PA6 decreased in the presence of PP‐MA. The presence of OMMT increased the tensile modulus as a function of OMMT loading due to the good dispersion of OMMT in the matrix. The insertion of polymer chains between clay platelets was verified by both XRD and TEM techniques. The viscosity of the nanocomposites decreased as PP‐MA loading increased due to the change in sizes of PA6 dispersed phase, and the viscosity increased as OMMT loading increased due to the interaction between the clay platelets and polymer chains. The clay platelets were located at the interface between PP and PA6 as confirmed by both SEM and TEM. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crystalline structure and mechanical properties of wet‐spun dibutyrylchitin fibers and products of their alkaline treatment

Dibutyrylchitin was obtained during krill chitin esterification with butyric anhydride in the presence of perchloric acid. The wet spinning of a 14.5% solution in dimethylformamide created dibutyrylchitin filaments, which were treated with an alkali solution for chitin regeneration. Fiber samples with different degrees of chitin restoration were obtained, and their fine structure and mechanical properties were investigated. The restoration of the chitin structure resulted in a gradual increase in the degree of crystallinity, the density of the structured area, the tensile strength, and the average elongation at rupture and in a decrease in the diameter of the fibers. The crystallinity degree of fully regenerated chitin, the final product of alkaline hydrolysis, reached a value close to that of native chitin. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1861–1868, 2004