Fabrication of Polypropylene/Poly (Trimethylene Terephthalate) Blend Fibers with Highly Improved Resiliency and Preserved Mechanical Properties

The main aim of this study was to deal with one of the major drawbacks of polypropylene (PP) fibers, i.e. low resiliency, by incorporating poly (trimethylene terephthalate) (PTT) nano-fibrils as a dispersed material into the PP polymer matrix. Thanks to the special helical shape of the PTT polymer backbone, the incorporated nano-fibrils of the PTT polymer strengthened the resiliency of the blend fibers. The presence of 10 and 15?wt% of PTT in the blend fibers led to an approximately 20% increase in the resilience behavior, compared to pure PP fibers, with the mechanical properties of the PP matrix preserved. The development of the fibrillar structures during the different steps of the melt spinning process was confirmed by scanning electron microscopy (SEM), and the lowest mean diameter of the nano-fibrils was 64?nm for the hot drawn blend fiber samples consisting of 10?wt% of PTT. In summary, we suggest the optimized blend fiber samples produced in this research will be a promising candidate for a wide range of engineering applications.     

Fabrication of Polypropylene (PP)/Poly Trimethylene Terephthalate (PTT)/Nanoclay Nanocomposite Fibers with Tailored Properties

Abstract

The main aim of this study was to deal with one of the major drawbacks of polypropylene (PP) fibers, i.e., low resiliency and low dyeability, by incorporating polytrimethylene terephthalate (PTT) fibrils, as a dispersed material, and organoclay, as a nano-filler, into the PP polymer matrix. The presence of 10?wt% of PTT and 0.5–1?wt% organoclay in the PP nanocomposite fibers led to an approximately 18.5% and 45.5% increase in the resilience behavior and dye uptake, respectively, compared to pure PP fibers, without using highly toxic carriers. The lowest mean diameter of the nano-fibrils was 75?nm for the hot drawn nanocomposite fiber samples as measured by scanning electron microscopy (SEM). The results of DSC indicated that the presence of both PTT and organoclay significantly influenced the crystallinity of the PP which also confirmed their nucleating effects in the nanocomposite fiber.     

Microstructure,Rheology, and Potential Oil Absorbency of Poly(Butyl Methacrylate) and Poly(Hydroxyethyl Methacrylate) Blends

To prepare oil-absorptive polymers with moderate cross-linking structure, poly(butyl methacrylate) (PBMA) was synthesized as a linear hydrophobic polymer by suspension polymerization. In addition, hydroxyethyl methacrylate (HEMA), as a monomer, which could construct a network structure among the macromolecules via hydrogen bond interactions, was solution polymerized in dimethylacetamide (DMAc) with PBMA, yielding a polymer blend of PBMA and PHEMA. The solution of the polymer blend was investigated by rotational viscometry and extended rheometry. The results showed that the viscosity varied greatly with the temperature and shear rate for three different compositions. Fourier transform infrared (FTIR) spectra indicated that an entanglement or interlocking cross-linking structure of molecular chains was constructed by hydrogen bonds. The results from nuclear magnetic resonance (NMR) spectra exhibited a downfield movement of the proton peak as influenced by end groups or hydroxyls in the polymer chains. The rheological measurements demonstrated that the cross-linking structure greatly affected the rheological behavior of the blend solution. In addition, the cross-linking structure was also evaluated by oil absorbency of films.     

High-Speed Melt Spinning of Polylactide/Poly(Butyleneterephthalate) Bicomponent Fibers: Mechanism of Fiber Structure Development and Dyeing Behavior

Bicomponent fibers consisting of polylactide (PLA) as the sheath and poly(butylene terephthalate) (PBT) as the core were produced by high-speed spinning to obtain materials suitable for medical clothing. The higher-order structure of the PLA fiber component appeared to exhibit simple, alternately stacked, uniaxially oriented amorphous and crystalline regions. Therefore, fairly large tanδ peaks were observed for single-component PLA fibers, even when the orientation-induced crystallization was achieved by high-speed spinning. By conjugating PLA with PBT, although limited mutual interference with the crystallization of each component occurred, both the PLA (Mw?=?170,000, L-lactide content?=?98.7%) and PBT (intrinsic viscosity?=?0.835-0.865 dL/g) could crystallize on a high-speed spinning line, and the proposed formation of a shish-kebab-like structure in the PBT component enhanced the thermal stability of the bicomponent fibers, particularly resulting in shrink-proof properties. The bicomponent fibers developed herein could be deeply dyed at 98?°C, with results comparable to those of industrial polyester, and peeling of the PLA skin layer was rarely observed, even when the dyed fibers were flattened by a rubbing force.     

Swelling Parameters and Mechanical Properties of Functional Fibers Based on Butyl Methacrylate-Hydroxyethyl Methacrylate Copolymer

Butyl methacrylate-hydroxyethyl methacrylate (BMA-HEMA) copolymers were synthesized by the method of suspension polymerization. The copolymer fibers were prepared for absorbing liquid organic matter by gelation-spinning in a twin screw extrusion machine. The swelling parameters and mechanical properties were investigated, and the morphology was observed by scanning electron microscope (SEM). The results show that the degree of equilibrium swelling for the fibers increased with increasing the mass fraction of HEMA in the monomer feed when toluene, trichloroethylene, or chloroform were selected as organic absorbates. All of the interaction parameters, χ ₁, for the fibers and organic liquids were less than 0.5, with the order of the interaction parameters χ ₁ being as follows: toluene > trichloroethylene > chloroform. Average molecular weights between crosslink points, M _c, and effective crosslink density, V _e, were dependent on the selected organic liquids; for the different organic liquids, M _c and V _e were different. The breaking tenacity, initial modulus, and yield stress of the fibers increased with an increase in the mass fraction of HEMA. However, elongation at break and elongation at yield decreased with increasing the mass fraction of HEMA; in particular, for the mass fraction of HEMA equal to 15 wt%, the fiber did not yield, and underwent a brittle fracture.     

Rheological Properties and Microstructures of Hydroxyethyl Cellulose/Poly(Acrylic Acid) Blend Hydrogels

A simple in-situ method was introduced to prepare hydroxyethyl cellulose/poly(acrylic acid) (HEC/PAA) blend hydrogels by forming an interpenetrating network (IPN). Storage modulus (G′) and loss modulus (G″) were improved dramatically compared to HEC. To prove that hydrogen bonds and chemical crosslinking played major roles in improving the hydrogel strength and toughening, and to optimize the components of HEC/PAA blend hydrogels, a series of blend hydrogels with different ratios of HEC to PAA were designed and the corresponding Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), rheological tests, and swelling properties were compared. Crosslinked HEC/PAA blend hydrogel (mol/mol = 1:1) showed the best properties appropriate for opening up biomedical applications of the hydrogel.     

A Novel Strategy for Achieving High Melt Strength Polypropylene and an Investigation of Its Foamability

A novel and feasible strategy for preparing high melt strength polypropylene (HMSPP) was developed by a melt grafting reaction in the presence of macro-monomer vinyl polydimethylsiloxane (VS), co-monomer styrene (St), and initiator benzoyl peroxide through a one-step reactive extrusion. The rheological behaviors, melt strength, and foaming ability of HMSPP were studied. The results showed that VS and St were successfully grafted onto polypropylene (PP), and the weight average molecular weight, molecular weight distribution, and melt strength of HMSPP were dramatically increased compared with those of the virgin isotactic polypropylene (iPP). Especially, the melt strength of HMSPP increased from 0.022 N for the virgin iPP to 0.29 N, which made the foamability of HMSPP significantly improved when supercritical carbon dioxide was used as the blowing agent. The foaming condition was optimized to 160°C and 14 MPa, for which HMSPP foams with a high expansion ratio of 66 times and a high cell density of about 5.8×10⁷ cell/cm³ were obtained, while the virgin iPP did not yield foams with good cell structure. Moreover, the resultant HMSPP could be foamed in a remarkably wide temperature range from 145°C to 165°C, which would be of great significance for industrial application.     

Structure and Properties of Glass Fiber Reinforced Polypropylene/Liquid Crystal Polymer Blends

A liquid crystal polymer (LCP) was used to improve the physical properties of glass fiber reinforced polypropylene (GFRPP). The LCP was beneficial to improve the mechanical and heat resistant properties of the GFRPP/LCP composite. Compared with the GFRPP with 30% (w%) glass fiber (GF), the yield strength and the impact strength for the GFRPP/LCP composites increased by 62.7% and 18.1%, respectively, with a 6.8°C increase in the Vicat softening temperature for a 5% LCP addition to the GFRPP composites. The crystallinity of the polypropylene (PP) matrix for the GFRPP/LCP composites increased for 5% LCP and then decreased with increasing the LCP content. The γ-phase crystals for the PP matrix occurred in the shear layer of the injection molded GFRPP/LCP samples. The improved adhesion interface between the GF and the PP matrix was beneficial to reinforce and toughen the GFRPP/LCP composites with a small addition of the LCP.     

Fiber Structure,Tensile Behavior and Antibacterial Activity of Polylactide/Poly(butylene terephthalate) Bicomponent Fibers Produced by High-Speed Melt-Spinning

Abstract

Various types of bicomponent fibers composed of polylactide (PLA) and poly(butylene terephthalate) (PBT) with different molecular weights, arranging the polymers separately in the skin or core, were produced by high-speed melt-spinning. The bicomponent spinning, arranging the PLA with high molecular weight (melt flow rate =1.9?g/10?min, L-lactide content = 98.7%) in the skin and the PBT with low molecular weight (IV = 0.835–0.865 dL/g) in the core, resulted in orientation-induced crystallization in the PLA component at the spinning speed of 2?km/min. This crystallization effect was ascribed to a chain-extending treatment applied to the original PLA (MFR = 4.0?g/10?min) to increase its molecular weight. By the treatment the PLA could crystallize when spun even at 1?km/min in its single-component spinning. On the other hand, the bicomponent spinning system interfered with the orientation-induced crystallization of PBT in the core. As a result, the critical spinning speed needed to generate the orientation-induced crystallization in the core PBT was elevated to 4?km/min. The inferior tensile behavior of the bicomponent fibers, as compared to the single-component PLA or PBT fibers, suggested poor compatibility between PLA and PBT. Transesterification reactions rarely occurred at the interface of the two polymers. The bicomponent fibers prepared from high molecular weight PLA and low molecular weight PBT, however, showed sufficient antibacterial activity and physical properties to be suitable for designing medical clothing materials.     

Nanofilled Polypropylene/Poly(trimethylene terephthalate) Blends: A Morphological and Mechanical Properties Study

Polypropylene (PP) /poly(trimethylene terephthalate), (PTT), binary blends in the presence of two interfacial modifier as well as two organically modified nanoclay additives were studied in terms of mechanical and morphological characteristics. Scanning electron microscopy confirmed the incompatibility of the system which was solved to some extent through incorporating the nanoclay as well as functional compatibilizers. An evaluation of the specimens via static mechanical tests in tensile mode gave credence to the assumption that the higher the PTT content, the higher the mechanical performance would be. Furthermore, the compatibilizer-containing blends not only exhibited higher toughness, but also possessed enhanced stiffness when a maleated compatibilizer was added. The tensile modulus was promoted further in the presence of clay nanoparticles; however, toughness was somewhat sacrificed. The Barentsen as well as Halpin-Tsai models were found to describe the binary blends modulus. The reinforcing impact of the nanoclay was exploited to a greater degree in the presence of the compatibilizer.     

Phase Structure,Thermal, and Mechanical Properties of Polypropylene/Hollow Glass Microsphere Composites Modified with Maleated Poly(ethylene-octene)

Maleated poly(ethylene-octene) (POE-g-MAH), as a compatilizer and toughener, was incorporated in polypropylene/hollow glass microspheres (PP/HGM) binary composites, and the phase structure and thermal and mechanical properties of these composites were investigated. Scanning electron microscopy analysis indicated that the phase structure of ternary composites could be controlled by POE-g-MAH and the surface treatment of HGM. Fourier transform infrared spectroscopy revealed that there was an amidation reaction between the treated HGM and POE-g-MAH during melt compounding. Differential scanning calorimetry suggested that the crystallization and melting behaviors of ternary composites were influenced by phase structure. Evaluation of mechanical properties showed that the amide linkage between the treated HGM and POE-g-MAH was favorable for improving the properties of ternary composites.     

Hydrophobic Modification of Poly(Ethylene Terephthalate) with Epoxy-Modified Polysiloxane by Reactive Extrusion

Hydrophobic poly(ethylene terephthalate) (PET) was prepared by reactive blending of PET with double epoxy groups modified polysiloxane (diepsi) or multiepoxy groups modified polysiloxane (multiepsi). The structure of the modified PET was characterized by ¹H NMR and intrinsic viscosity. The grafted ratio of diepsi and multiepsi was 1.3 and 0.03 wt%, respectively. With the introduction of diepsi and multiepsi to PET, the water contact angle of modified PET increased from 73° to a maximum of 106°, showing the good hydrophobicity of the modified PET. The samples of modified PET were washed with different solvents and their water contact angles did not significantly decrease, indicating good durability of the hydrophobicity. Moreover, the films of modified PET prepared by solution casting (phenol and 1, 1, 2, 2-tetrachloroethane mixed solution) showed excellent hydrophobicity with the contact angle 151°. Scanning electron microscopy images showed the surface of the modified PET films to be rougher than those of unmodified PET because the introduction of polysiloxane to PET resulted in phase separation during the solvent evaporation process.     

Thermoplastic Elastomers Based on Natural Rubber/Polypropylene Blends: Effect of Blend Ratios and Dynamic Vulcanization on Rheological,Thermal, Mechanical,and Morphological Properties

Thermoplastic elastomers (TPEs) based on natural rubber (NR)/polypropylene (PP) with different blend ratios were prepared and studied. The TPEs were obtained by dynamic vulcanization of NR/PP using a sulfur (S)/N-tert-butyl-2-benzothiazolesulphenamide (TBBS) and tetramethylthiuram disulphide (TMTD) curative system during processing in the melt state in an internal mixer equipped with cam rotors. Rheological, thermal, mechanical, dynamic, and morphological properties of the TPEs prepared were investigated. Based on this study a mechanism for the NR crosslinking was proposed where the sulfur vulcanization occurs through radical substitution in the forms of polysulfide bridges. The dynamic vulcanization process increases the stiffness of the NR phase in the TPEs and modifies the rheological and thermal behavior of the system compared to the behavior of the basic material PP. The crosslinked NR particles restrict the spherulitic growth and the regular arrangement of the spherulites of PP phase, decreasing the crystallinity degree. On the other hand, a reduction of mobility of the chain segments was also observed and, consequently, an increase of the T_g values. NR/PP TPEs with high content of NR showed superior mechanical performance compared to the uncrosslinked NR/PP blends in terms of tensile strength, Young's modulus and hardness. An increase of approximately 320% in Young's modulus values was obtained for the NR70/PP30 TPE compared to NR70/PP30. Morphological studies revealed the formation of large aggregates of NR domains in NR/PP TPEs which increased in size with an increase of the rubber content.     

The Effect of Poly(Ethylene Succinate) on Mechanical Properties of PLLA/PES Blend Prepared by Melt-Blending

Fully biodegradable poly(L-lactide) and poly(ethylene succinate) (PLLA/PES) blends were prepared via melt-blending using PLLA and PES as reactants in a stainless steel chamber. The prepared PLLA/PES blend, as well as neat PLLA and PES, was characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) to confirm the structure and the crystallization of PLLA in the blend. The mechanical properties of PLLA/PES blends were determined by bending and tensile tests and the effects of PES content on the mechanical properties of PLLA/PES blends were investigated. It was found that blending some amount of PES could significantly improve the elongation at break while still keeping considerably high strength and modulus. With increasing PES content, both strength and modulus gradually decreased; however the elongation at break significantly increased. SEM was used to examine the morphology of fracture surfaces of PLLA/PES blends.     

Phase Structure of Polyamide 6/Poly(styrene-co-acrylonitrile) and Poly(styrene-b-(ethylene-co-butylene)-b-styrene) or Poly(maleated Styrene/Ethylene-co-Butylene/Styrene) Ternary Blends

Two sets of ternary blends; polyamide 6/poly(styrene-co-acrylonitrile)/poly(styrene-b-(ethylene-co-butylene)-b-styrene) (PA6/SAN/SEBS) and polyamide 6/poly(styrene-co-acrylonitrile)/poly(maleated styrene/ethylene-co-butylene/styrene) (PA6/SAN/SEBS-g-MA), based on 70 wt% of matrix and 30 wt% of the dispersed phases at various concentrations of the minor components, were prepared via melt blending. Morphologies of the ternary systems were studied using scanning electron microscopy (SEM) and compared with the predictions of the spreading coefficient (SC), minimum relative interfacial energy (RIE), and dynamic interfacial energy (DIE) phenomenological models. The effects of different reported surface tensions of the used polymers and different protocols of the core-shell ratio calculation on the prediction of the models were investigated. The core-shell structure for PA6/SAN/SEBS system and two separate minor phases for PA6/SAN/SEBS-g-MA were observed at all of the compositions. The results indicated that the most important parameter for the accurate prediction of the models is the accurate calculation of the interfacial tension of the used polymers, in both the static and dynamic conditions.     

Influence of Mixing Technique on Microstructure and Impact Properties of Isotactic Polypropylene/ Poly(Cis-Butadiene) Rubber Blends

Isotactic polypropylene/poly(cis-butadiene) rubber (iPP/PcBR vol%: 80/20) blends were prepared by melt mixing with various mixing rotation speeds. The effect of mixing technique on microstructure and impact property of blends was studied. Phase structure of the blends was analyzed by scanning electron microscopy (SEM). All of the blends had a heterogeneous morphology. The spherical particles attributed to the PcBR-rich phase were uniformly dispersed in the continuous iPP matrix. With increase of the mixing rotation speed, the dispersed phase particle's diameter distribution became broader and the average diameter of the separated particles increased. The spherulitic morphology of the blends was observed by small angle light scattering (SALS). Higher mixing rotation speed led to a more imperfect spherulitic morphology and smaller spherulites. Crystalline structure of the blends was measured by wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS). The introduction of 20 vol% PcBR induced the formation of iPPβ crystals. Higher rotation speed led to a decrease in microcrystal dimensions. However, the addition of PcBR and the increase of mixing rotation speed did not affect the interplanar distance. The long period values were the same within experimental error as PcBR was added or the mixing rotation speed quickened. The normalized relative degree of crystallinity of the blends slightly increased under lower rotation speeds (30 and 45 rpm) and decreased under higher rotation speeds. The notched Izod impact strength of the blends was enhanced as a result of the increase of mixing rotation speed.     

Unusual Phase Separation Kinetics in Poly(Methyl Methacrylate)/Poly(Styrene-co-Acrylonitrile) (PMMA/SAN) Blends with PMMA of Different Molecular Weights

The influence of molecular weight of poly (methyl methacrylate) (PMMA) on the thermodynamics and dynamics of phase separation in PMMA/poly (styrene-co-acrylonitrile) (SAN) blends was investigated via optical microscopy, time-resolved small-angle light scattering (SALS), and dynamic rheological measurements. It was found that the cloud point temperature of the blends decreased with an increase in the molecular weight of the PMMA. The phase separation rates of PMMA 48K/SAN and PMMA 85K/SAN blends with the near-critical composition were almost the same at small quench depths due to the limited mobility of molecular chains at low temperatures. However, an unexpected phase separation dynamics was observed at larger quench depths. Not only the morphology evolution but also the apparent diffusion coefficient D_app calculated from SALS revealed that the phase separation rate was faster in the PMMA 85K/SAN blend than in the PMMA 48K/SAN blend. The possible reasons for this unusual rapid kinetics of phase separation observed in the higher molecular weight blend were discussed in terms of molecular mobility and viscoelasticity.     

Effects of Viscosity Ratio on Morphological,Rheological and Mechanical Properties of PP/PBT Melt Spun Alloy Fibers

Phase morphology formation plays an important role in the mechanical properties of polymer alloy fibers. The development of the blend morphology depends not only on the intrinsic properties of the component polymers but also on extrinsic factors such as viscosity ratio, λ, in the melt spinning process. The effects of blend component viscosity ratio on the morphological, rheological, and mechanical properties of polypropylene/poly(butylene terephthalate) (PP/PBT) melt spun alloy fibers were investigated. Accordingly, two kinds of PP as matrix phase and two kinds of PBT as dispersed phase, with various melt viscosity, were physically mixed and then blended during the extrusion step of melt spinning. SEM micrographs and rheological and mechanical properties evaluations showed that the morphology of PP/PBT alloy fibers strongly depend on the viscosity ratio, λ. Finer diameter PBT fibrils were observed for Viscosity ratios less than 1 (λ < 1) compared to samples with λ > 1. The best mechanical properties in alloy fiber samples were obtained for the viscosity ratio closest to unity (sample with λ = 0.9). The lowest differences among measured complex viscosities at various shear rates (0.1, 10, and 100 s^?1) were also observed in samples with λ = 0.9. The results showed that the mechanical properties of alloy fiber samples are affected not only by morphological properties observed at different viscosity ratios but also by the properties of the individual polymer components.     

Isothermal Crystallization and Miscibility of Isotactic Polypropylene/Poly(cis-butadiene) Rubber Blends

Isotactic polypropylene/poly(cis-butadiene) rubber (iPP/PcBR) blends were prepared by melt mixing. Isothermal crystallization and miscibility for neat iPP and blends of iPP/PcBR were investigated by differential scanning calorimetry. The presence of PcBR remarkably affected isothermal crystalline behaviors of iPP. An addition of PcBR caused shorter crystallization time and a faster overall crystallization rate, meaning a heterogeneous nucleation effect of PcBR upon crystallization of iPP. For the same sample, the crystallization peak was broader and the supercooling decreased as the crystallization temperature increased. The Avrami equation was suitable to describe the primary isothermal crystallization process of iPP and blends. The addition of PcBR led to an increase of values of the Avrami exponent n, which we suggest was because the blends had a stronger trend of instantaneous three-dimensional growth than neat iPP. The equilibrium melting point depression of the blends was observed, indicating that the blends were partly miscible in the melt.     

Structure and Mechanical Properties of 50/50 NR/SBR Blend/Pristine Clay Nanocomposites

A blend/clay nanocomposites of 50/50 (wt%) NR/SBR was prepared via mixing the latex of a 50/50 NR/SBR blend with an aqueous clay dispersion and co‐coagulating the mixture. The structure of the nanocomposite was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Nanocomposites containing less than 10 phr clay showed a fully exfoliated structure. After increasing the clay content to 10 phr, both nonexfoliated (stacked layers) and exfoliated structures were observed in the nanocomposites. The results of mechanical tests showed that the nanocomposites presented better mechanical properties than clay‐free NR/SBR blend vulcanizate. Furthermore, tensile strength, tensile strain at break, and hardness (shore A) increased with increasing clay content, up to 6 phr, and then remained almost constant.