Physico-mechanical properties of poly (vinyl alcohol), poly (vinyl alcohol)/boric acid,and poly (vinyl alcohol) nanocomposites incorporated with amino-functionalized and pristine halloysite nanotubes films

Eco-friendly poly(vinyl alcohol) (PVA), PVA/boric acid, PVA/halloysite nanotubes (HNTs), and PVA/amino-functionalized HNTs (APTES-HNTs) films were fabricated by a solution casting technique. The samples were characterized by fourier transform infrared, X-ray diffraction, differential scanning calorimetry, scanning electron microscope, and energy-dispersive spectroscopy. The characterization results proved the chemical and physical interactions between the PVA and different additives. The viscoelastic behavior of the films was evaluated by DMA and creep analysis. The storage modulus, loss factor, and both α_α and β_β transitions affected by APTES-HNTs as a potential filler to form effective cross-links. APTES-HNTs existence enhanced creep-recovery beyond expectations. Tensile and impact strength were measured to understand samples' mechanical stability. PVA/APTES-HNTs and PVA/boric acid showed more yield behavior after the elastic limit. Furthermore, the subsequent rupture and impact strength were increased significantly compared with neat PVA and PVA/HNTs. The viscoelastic and mechanical behaviors were linked to each other by the area under Tanδ curve and the work of rupture and impact strength, which their linear correlation coefficient is statistically significant at 95% confidence limits. It seems that the presence of APTES-HNTs provides new cross-links, which altered (improved) the physico-mechanical properties of PVA, offering a bionanocomposite suitable for further applications. From the literature, possible explanations are provided for these observations.     

Shear-induced crystallization of poly(phenylene sulfide)

The crystalline morphology of poly(phenylene sulfide) (PPS) isothermally crystallized from the melt under shear has been observed by polarized optical microscope (POM) equipped with a CSS450 hot-stage. The shish–kebab-like fibrillar crystal structure is formed at a higher shear rate or for a longer shear time, which is ascribed to the tight aggregation of numerous oriented nuclei in the direction of shear. The crystallization induction time of PPS decreases with the shear time, indicating that the shear accelerates the formation of stable crystal nuclei. Under shear, the increase of spherulite growth rate results from highly oriented chains. The melting behavior of shear-induced crystallized PPS performed by differential scanning calorimetry (DSC) shows multiple melting peaks. The lower melting peak corresponds to melting of imperfect crystal, and the degree of crystal perfection decreases as the shear rate increases. The higher melting peak is related to the orientation of molecular chains. These oriented molecular chains form the orientation nuclei which have higher thermal stability than the kebab-like lamellae that are developed later. A new model based on the above observation has been proposed to explain the mechanism of shish–kebab-like fibrillar crystal formation under shear flow.     

超支化聚苯硫醚与线性聚苯硫醚的对比表征

以2,4-二氯苯硫酚为原料,采用一步法合成超支化聚苯硫醚。笔者运用红外光谱、拉曼光谱、荧光光谱、示差扫描量热分析、热重分析、广角X-射线衍射、溶解实验等分析手段,对超支化聚苯硫醚和线性聚苯硫醚的基本性能进行了对比。由于两者结构上的差异,使得两者表现出不同的特性。超支化聚苯硫醚具有三取代苯结构,具有很强的荧光效应、完全的不结晶、溶于有机溶剂、热降解温度低于线性聚苯硫醚约60℃等特性。广角X-射线衍射谱图也和结晶、无定型线性聚苯硫醚有很大不同。     

Realization of reinforcing and toughening poly (phenylene sulfide) with rigid silica nanoparticles

Reinforcing and toughening poly (phenylene sulfide) (PPS) with rigid SiO₂ nano-particles was realized simultaneously under the suitable thermodynamic state of PPS, and the key issue about the effect of matrix/filler interaction was also demonstrated. The strong matrix/filler interaction realized by grafting reactive groups onto nanoparticles was beneficial for stress transfer and thus in favor of the increase in tensile strength of PPS. Meanwhile, this interaction provided nanoparticles with certain mobility to move with molecular chains and align along the tensile direction when T > T_g of PPS, thus the nanoparticles could significantly improve the tensile toughness of PPS according to the energy dissipation mechanism. Consequently, the tensile strength and elongation to break values of PPS increased to 59.0 MPa and 112.1 % from the initial values of 48.0 MPa and 78.5 % by adding 1 wt% grafted SiO₂ nano-particles. The work provided a promising method to reinforce and toughen rigid-chain polymer simultaneously and prepare high-performance PPS nanocomposites.     

Toughening of epoxy thermosets with nano-sized or micron-sized domains of poly(ethylene oxide)-b-poly(butadiene-co-acrylonitrile)-b-poly(ethylene oxide) triblock copolymers synthesized using room temperature ester coupling reaction

Poly(ethylene oxide)-b-poly(butadiene-co-acrylonitrile)-b-poly(ethylene oxide) (PEO-b-PBN-b–PEO) triblock copolymers with three different compositions were synthesized from poly(ethylene glycol) methyl ethers and carboxylic acid-terminated poly(butadiene-co-acrylonitrile) (CTBN) by ester coupling reaction at room temperature. The PEO-b-PBN-b-PEO was incorporated into anhydride cured epoxy thermosets to improve the fracture toughness by the formation of either nano-sized spherical micelles or micron-sized vesicles. The polymer chemical structure was confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and gel permeation chromatography. The morphology of PEO-b-PBN-b–PEO within the epoxy thermosets was investigated using a transmission electron microscope, an atomic force microscope, and a scanning electron microscope. Also, we conducted impact testing and plane-strain fracture toughness testing to evaluate the fracture toughness in terms of the impact strength and the critical stress intensity factors (K_IC) for the modified epoxy thermosets. The results revealed that all the PEO-b-PBN-b-PEO triblock copolymers are more effective in the toughening of epoxy thermoset compare to CTBN. We found that the 5 wt% PEO-b-PBN-b-PEO modified epoxy thermoset containing micron-sized vesicles exhibited the highest K_IC, which was 3.23 times as high as the K_IC of pristine epoxy thermoset. Besides, the glass transition temperature remained and the tensile modulus did not reduce remarkably when the amount of PEO-b-PBN-b-PEO added into epoxy was 5 wt%.     

Processing,structure, and properties of multiwalled carbon nanotube–poly(phenylene sulfide) composite fibers

To improve the processability and properties of the poly(phenylene sulfide) (PPS) fibers at room temperature and high temperatures, a series of composite fibers based on PPS and multiwalled carbon nanotubes were prepared by melt spinning. We researched the processability with a high‐pressure capillary rheometer, and the properties of the composite fibers were investigated in detail by scanning electron microscopy, differential scanning calorimetry, fiber sonic velocity measurement, and single‐fiber strength testing. The results show that the carbon nanotubes (CNTs) had good interfacial adhesion with PPS and dispersed homogeneously in the PPS matrix. When the shear rate was higher than 500 s^?1, the oriented CNTs induced the orientation of PPS molecular chains; this resulted in a decline in the apparent viscosity and an increase in the orientation degree of the molecular chains. Meanwhile, the CNTs acted as nucleating agents to effectively improve the crystallization of PPS. The strength of the fibers at room temperature were improved by 28.8% after the addition of 0.2% CNTs, and the initial modulus was also significantly enhanced. The strength retention at 160 °C was promoted from 60.58 to 88.32% with the addition of 1.0% CNTs. The shrinking percentage decreased to almost zero from higher than 15%; this suggested that the CNTs could efficiently improve the dimensional stability at high temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44609.     

Thermal degradation of poly(phenylene sulfide) and perfluoropoly(phenylene sulfide)

The thermal and oxidative degradation of poly(phenylene sulfide) and perfluoropoly(phenylene sulfide) have been studied by a weight-loss method. The products of breakdown in vacuum have also been analyzed. The poly(phenylene sulfide) is more thermally stable in inert and oxidizing atmospheres than the fully fluorinated analog. The breakdown products can be accounted for by chain scission and transfer reactions. The formation of a large proportion of residue implies that crosslinking reactions play an important part in the degradation.     

Strengthening,toughening, and self-healing for carbon fiber/epoxy composites based on PPESK electrospun coaxial nanofibers

A carbon fiber/epoxy composite modified by electrospun coaxial dicyclopentadiene/poly(phthalazinone ether sulfone ketone) (DCPD/PPESK) nanofibers was successfully fabricated, and the addition of DCPD/PPESK fibrous membranes made the composite have remarkable self-healing ability, and meanwhile effectively improve its mechanical properties. Results of polarization microscope observation and thermogravimetric analysis confirmed liquid DCPD as the healing agent was encapsulated into the PPESK coaxial nanofiber. Three-point bending test was utilized to evaluate the mechanical properties and self-healing effect of the composite. Experimental results indicated that the embedded nanofibers significantly improved the toughness of the composite, and maintained good mechanical properties even at low resin content. Most importantly, the flexural strength of the composite recovered to close to 90% observed 2 h after the bending failure.     

Tunable fluorescent and antimicrobial properties of poly(vinyl amine) affected by the acidic or basic hydrolysis of poly(N-vinylformamide)

Synthesis of poly(N-vinylformamide) (PNVF) and its subsequent hydrolysis to convert it to poly(vinyl amine) (PVAm) were performed. Kinetics of acidic and basic hydrolysis of poly(N-vinylformamide) (PNVF), and products of hydrolysis were investigated by using Fourier transform infrared, size exclusion chromatography, ¹H NMR, and ¹³C NMR spectroscopies, and thermogravimetric analysis. It was observed that amide groups did not completely transform into amine groups by acidic hydrolysis of PNVF while the conversion of amides into amine groups via basic hydrolysis of PNVF was complete in 12 h, as confirmed by spectroscopic measurements. Results of extensive characterization revealed significant structural and conformational differences between acidic and basic hydrolysis products. Fluorescence spectroscopy was used for the first time to follow the conversion of amide groups into amine groups. The fluorescence intensity of PVAm obtained from basic hydrolysis of PVNF showed significant increase with amide/amine conversion. Finally, PVAm obtained from acidic hydrolysis of PNVF demonstrated potent antimicrobial activity, 10–20 times more, against common pathogens for example, C. albicans as fungal strain and E. coli, S. aureus, B. subtilis, and P. aeruginosa as bacterial strains as compared to PVAm obtained from basic hydrolysis.     

Microcellular foaming of poly(phenylene sulfide)/poly(ether sulfones) blends using supercritical carbon dioxide

Microcellular foaming of poly(phenylene sulfide)/poly(ether sulfones) (PPS/PES) blends presents a promising approach to produce high‐performance cellular materials with tailored microstructures and enhanced properties. This study investigated the effects of multiphase blend composition and process conditions on the foaming behaviors and final cellular morphology, as well as the dynamic mechanical properties of the solid and microcellular foamed PPS/PES blends. The microcellular materials were prepared via a batch‐foam processing, using the environment‐friendly supercritical CO₂ (scCO₂) as a blowing agent. The saturation and desorption behaviors of CO₂ in PPS/PES blends for various blend ratios (10 : 0, 8 : 2, 6 : 4, 5 : 5, 4 : 6, 2 : 8, and 0 : 10) were also elaborately discussed. The experimental results indicated that the foaming behaviors of PPS/PES blends are closely related to the blend morphology, crystallinity, and the mass‐transfer rate of the CO₂ in each polymer phase. The mechanisms for the foaming behaviors of PPS/PES blends have been illustrated by establishing theoretical models. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42634.     

Highly-modified polylactide transparent blends with better heat-resistance,melt strength,toughness and stiffness balance due to the compatibilization and chain extender effects of methacrylate-co-glycidyl methacrylate copolymer

A core-shell modifier with the cross-linked acrylate and silicone copolymer as the core and polymethyl methacrylate (PMMA) as the shell (PASi-g-PMMA) was used to toughen the brittle polylactide (PLA). In addition, the copolymer of methyl methacrylate (MMA) and glycidyl methacrylate (GMA) (MG) was utilized to further enhance the modification efficiency of the PASi-g-PMMA. The MG copolymer played the double roles of compatibilizer and chain extender, which not only improved the interfacial adhesion between the PLA and PASi-g-PMMA particles, but also increased the molecular weight and chain entanglement of the PLA. Compared with the PASi-g-PMMA toughened PLA blend, the PLA/PASi-g-PMMA/MG blends showed much higher heat-resistance, melt strength, transparency, toughness and stiffness balance. When the PASi-g-PMMA content was 20 wt%, 20 wt% MG increased the glass transition temperature (T_g), complex viscosity (η*), transparency, impact and tensile strength of PLA/PASi-g-PMMA blend from 60.1°C, 1.9 × 10³ Pa·s, 76.1%, 748 J/m and 37 MPa to 71.5°C, 0.5 × 10⁴ Pa·s, 78.4%, 860 J/m and 45 MPa for the PLA/PASi-g-PMMA/MG blend. This research provided a facile and practical method to overcome the shortcomings of the PLA and promoted its application in broader fields.     

Elastomer-toughened poly(phenylene sulfide)

For use as electrical and electronics parts, or automobile and mechanical parts, toughened poly(phenylene sulfide) (PPS) is desired. For these applications, our investigation centered on improving the toughness of PPS and developing elastomer-toughened PPS and elastomer-toughened compounds of PPS. Using chemically treated PPS and an olefinic elastomer with a functional group, we developed elastomer-toughened PPS using a reactive processing method. In the PPS matrix, the elastomer is finely dispersed. While the notched Izod impact strength of the original PPS is about 1 kg · cm/cm. clastomer-toughened PPS has a notched impact strength around 50 kg · cm/cm. The notched fracture surface of elastomer-toughened PPS is observed using a scanning electron microscope. We concluded that the mechanism for the toughening is attributed to energy dissipation by matrix yield.     

Thermomechanical properties and morphology of interpenetrating polymer networks of polyurethane–poly(methyl methacrylate)

Interpenetrating networks (IPNs) of polybutadiene‐based polyurethane (PU) and poly(methyl methacrylate) (PMMA) were synthesized. The effect of the incorporation of 2% glycidyl methacrylate (GMA) and 2‐hydroxyethyl methacrylate (2‐HEMA) on the thermal, mechanical, and morphological properties of IPNs was investigated. Both 2‐HEMA and GMA led to improvements in these properties. However, 2‐HEMA‐containing IPNs showed somewhat better tensile strength, elongation, and damping characteristics. The morphology of IPNs containing 2‐HEMA showed better mixing of the components. The improvement in the properties was observed for up to 40% PMMA in the IPNs. Differential scanning calorimetry thermograms showed the presence of three glass transitions. The third glass‐transition temperature was explained by possible grafting of methyl methacrylate onto PU. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1576–1585, 2002     

Thermal studies of blends of poly(phenylene sulfide) (PPS) with poly(phenylene sulfide sulfone) (PPSS) and with poly(phenylene sulfide ether) (PPSE)

The miscibilities of poly(phenylene) sulfide/poly(phenylene sulfide sulfone) (PPS/PPSS) and poly(phenylene) sulfide/poly(phenylene sulfide ether) (PPS/PPSE) blends were invesigated in terms of shifts of glass transition temperatures T_g of pure PPS, PPSS, a dn PPSE. The crystallization kinetics of PPS/PPSS blends was also studied as a function of molar composition. The PPS/PPSS and PPS/PPSE blends are respectively partially and fully miscible. PPSE shows a plasticizing effect on PPS as does PPS on PPSS, which necessarily improves te processibility in the respective systems. We can control T_g and melting temperature T_m of PPS by varying amounts of PPSE in blends. The melt crystallization temperature T_mc of PPS/PPSE blends was higher than that of the PPSE homopolymer. Therefore, these blends require shorter cycle times in processing than pure PPSE. The overall rate of crystallization for PPS/PPSS blends follows the Avrami equation with an exponent ?2. The maximal rate of crystallization for PPS/PPSS blends occurs at a temperatre higher by 10°C than that for PPS, while the crystallization half time t_1/2 is 4 times shorter. In the cold crystallization range, crystal growth rates increase and Avrami exponents decrease significantly as the temperature increases.     

Acrylonitrile–butadiene rubber functionalization for the toughening modification of recycled poly(ethylene terephthalate)

The incorporation of functionalized acrylonitrile–butadiene rubber (NBR) into recycled poly(ethylene terephthalate) (PET) was introduced as an effective route for modifying the properties of PET and as a new method for PET recycling as well. To achieve modified NBR, glycidyl methacrylate (GMA) was grafted onto NBR with optimized reactive mixing, in which the highest grafting degree and lowest gel content were generated. PET/NBR blends with and without GMA functionalization were produced by melt mixing, and the mechanical properties, dynamic mechanical thermal properties, and phase morphologies of the systems were determined and compared. We found that low amounts of peroxide initiator (dicumyl peroxide) and high levels of the GMA monomer in the presence of the styrene comonomer led to the maximum grafting degree and suppressed the competing rubber crosslinking and GMA homopolymerization reactions. The blend compatibility with PET determined from dynamic mechanical thermal analysis spectra and scanning electron microscopy images was greatly improved when the NBR‐grafted GMA was used instead of the neat NBR in the blend recipes. As a result, the rubber phase dispersed in the PET matrix more finely, and the impact strength of the blend advanced very significantly. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40483.     

Improvement of mechanical properties of polylactide by equal channel multiple angular extrusion

The combination of high strength and toughness is always the goal of high-performance polymer materials for industrial use. This study addresses the potentialities of a solid state equal-channel multiple-angular extrusion (ECMAE) in production of polylactide (PLA) with simultaneous improvement in toughness, strength, and thermal stability. Chain extender Joncryl was used to form PLA with different chain length and morphology (linear or branched PLA). It is demonstrated that simple shear deformation implemented in ECMAE results in formation of an orientation order, an increase in the degree of crystallinity, and the creation of α crystals with an increased degree of perfection. The value of the effects achieved depends on the type of PLA morphology. The best result is observed in the case of linear PLA. ECMAE-modified linear PLA possess the better combination of strength, modulus, and ductility than the branched one. Compared with neat linear PLA, ECMAE-modified linear PLA shows 12%, 26%, 217%, and 40% increase in tensile strength, Young's modulus, strain at break and impact strength, respectively. Additionally, the storage modulus shows an improved thermal stability of ECMAE-modified PLA.     

Irradiation processing of immiscible PP/EOC blend: Morphology control and processability modification

In this study, applying electron beam irradiation method at a relatively low-irradiation dose (20 kGy) under the air atmosphere to prepare injectable polypropylene (PP)/ethylene-octene copolymer (EOC) blends with fine morphology and appropriate performance was investigated. For this purpose, an extrusion PP grade with an EOC grade suitable to improve its impact resistance was melting blended. Gel content and rheological measurements revealed long-chain branching is predominant phenomenon occurring during the irradiation process of EOC. Blend irradiation resulted in changing its melt flow index proper for injection molding. A fine morphology obtained for the unirradiated blend was preserved for the irradiated blend. Moreover, irradiation thermally stabilized the blend morphology. Blends linear viscoelastic behavior discussed by proper rheological models revealed the existence of interfacial interactions and a reduction of the interfacial tension between irradiated blend phases. No significant effect of irradiation on the crystallization characteristics of EOC and the blend was observed. The satisfying impact resistance of the irradiated blend was near to that of the unirradiated blend, although its tensile mechanical properties were less.     

Correlating ultra-toughening of bio-based polyamide 410 with melt rheological and solid state relaxation dynamics by gelation rheology approach

The sol–gel or viscous-elastic transitions of the bio-based polyamide 410/POE-g-MA (polyethylene-co-octene copolymer grafted with maleic anhydride) blends have been systematically discussed in the framework of melt rheology as assessed on a parallel plate rheometer set-up in small amplitude oscillatory shear mode and solid state dynamic mechanical relaxation measurements. The viscous response dominated enhancement in elastic moduli of the blends that was characterized by the phase transitions across the composition range of 10–15 wt% of POE-g-MA. A direct correlation between the gel point (estimated from the cross-over of frequency-independent loss tangent curves) and the ultra-toughness (maximized to an extent of ~15-fold increase in notched Izod impact strength) could be established vis-a-vis its corroboration from the morphology of the impact-failed surfaces. The extent of maleic anhydride (−MA) content induced phase interaction with polyamide 410 via the formation of a polyamide-co-(polyoctene-co-ethylene) type copolymer linkage in solid-state and its subsequent impact on solid-state damping was analyzed. The study establishes qualitative correlation between ultra-toughening of polyamide 410 to that parameters based on relaxation dynamics measurements using melt rheology and solid-state dynamic responses conforming to the principles of gelation rheology.     

Structure and properties development in poly(phenylene sulfide) fibers. II. Effect of one-zone draw annealing

In this article, we discuss the role of one-zone drawing followed by annealing in enhancing the structure and properties of fibers manufactured from Fortron^® linear poly(phenylene sulfide) resins. The interaction effects of the polymer molecular weight (MW), melt-spinning process parameters, and draw-annealing process conditions were also elucidated. Several tools used to probe the investigation were tensile testing, differential scanning calorimetry, polarized light optical microscopy, wide-angle X-ray scattering, and small-angle X-ray scattering. This study showed that the optimum drawing temperature was around 95°C. A considerable improvement in the fiber tensile properties was observed upon drawing and annealing under optimum processing conditions. Fibers with tenacities close to 5 g/den were obtained. The development of the tensile properties was statistically correlated with the morphological changes in the fibers. The routes to achieving fibers with optimum tensile properties were shown to be different for resins with different MWs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012