Mechanical properties and network structure of phenol resin crosslinked hydrogenated acrylonitrile‐butadiene rubber

The tough and stretchable crosslinked hydrogenated acrylonitrile–butadiene rubber (HNBR) could be prepared by resol type phenol resin as a crosslinker. The mechanical properties and the network structure of the phenol resin crosslinked HNBR were investigated by comparing with those of the peroxide crosslinked HNBR having the higher crosslink density and the heterogeneous network structure. The elastic modulus and the strain at break of the phenol resin crosslinked HNBR were much higher than those of the peroxide one. The residual strain was below 20 % after stretching up to 650 % and then releasing from the cramps. Since the crosslink density is low, the high elastic modulus and the good recovery deformation are attributed to the stiffness and rigidity of the crosslink junctions obtained by phenol resin. Small‐angle X‐ray scattering measurements revealed that the network structure is spatially homogeneous and the results of the wide angle X‐ray diffraction indicate that the strain‐induced crystallization is suppressed, which enable the longer elongation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Crack growth of natural rubber filled with functionalized silica particles

In the present work, functionalized liquid isoprene rubber (FLIR) was used to improve the filler dispersion and filler–rubber interaction in the silica filled natural rubber system. By the infrared spectra and scanning electron microscopy, it was proved that the FLIR was successfully grafted on the silica and the functionalized silica was dispersed in the NR matrix homogeneously. Based on the real‐time crack tip morphology monitoring method, the influence of FLIR on the crack growth behavior of NR filled with silica was analyzed. By the adding of FLIR, the crack resistance of the natural rubber embedded with functionalized silica is remarkably increased. When the weight ratio of FLIR to silica is 3:10, the NR composite has the best crack resistance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42972.     

Thermo‐reversible healing in a crosslinked polymer network containing covalent and thermo‐reversible bonds

The self‐healing behavior of a modified ureido‐amide based thermoplastic hybrid elastomer was investigated by increasing the concentration of non‐reversible (covalent) bonds compared to reversible (hydrogen) bonds. A crosslinked polymer network was synthesized using varying amounts of diglycidylether of bisphenol A and reacting with the ureido‐amide thermoplastic. Increasing epoxy content produced a more rigid and thermally stable hybrid network, which in turn decreased overall thermo‐reversible or healing behavior. Fracture toughness recoveries varied from 25% for the system containing the greatest number of covalent bonds to well over 200% for systems containing higher thermoplastic content. Substantial levels of healing, about 62% recovery, were still achieved despite the crosslinked network having a T_g above room temperature, 31°C as measured by differential scanning calorimetry (DSC). Dynamic mechanical thermal analysis was used to monitor thermo‐reversible behavior of the elastic moduli and thus probe molecular mobility within the glassy state. The extent and rate of recovery of the elastic modulus was dominated by the extent of thermal activation above the glass transition temperature. Fourier transform infrared spectroscopic and DSC studies confirmed that reacting the thermoplastic with an epoxy resin produced a covalently bonded crosslinked network and the epoxide groups were completely consumed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Tailoring the crystalline morphologies and mechanical properties of high‐density polyethylene parts by a change in the fluid flow pattern under gas‐assisted injection molding

In this study, an increase in the cooling rate of high‐density polyethylene parts was carried out via a change in the fluid flow pattern to introduce gas cooling under a gas‐assisted injection‐molding process; this was conducive to the retention of orientation chains shaped during the injection stage and further developed into much more oriented crystals. Morphological observation showed that the parts without gas cooling (WOGC) were composed of oriented crystals except the gas channel zone, whereas the parts with gas cooling (WGC) were full of oriented crystals, especially much more interlocking shish‐kebab structures in the subskin zone. The WGC parts had a higher degree of orientation than the corresponding zone of the WOGC parts. Although the lower crystallinity, the wider orientation regions, and much more interlocking shish‐kebab structures led to considerable increases from 32 and 990 MPa in the WOGC parts to 36 and 1150 MPa in the WGC parts for the yield strength and elastic modulus, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40349.     

Characterization of nanosilica‐filled epoxy composites for electrical and insulation applications

We report in this article the results of nanosilica (SiO₂)‐filled epoxy composites with different loadings and their electrical, thermal, mechanical, and free‐volume properties characterized with different techniques. The morphological features were studied by transmission electron microscopy, and differential scanning calorimetry was used to investigate the glass‐transition temperature (T_g) of the nanocomposites. The properties of the nanocomposites showed that the electrical resistivity (ρ), ultimate tensile strength, and hardness of the composites increased with SiO₂ weight fraction up to 10 wt % and decreased thereafter; this suggested that the beneficial properties occurred up to this weight fraction. The temperature and seawater aging had a negative influence on ρ; that is, ρ decreased with increases in the temperature and aging. The free‐volume changes (microstructural) in the composite systems correlated with seawater aging but did not correlate so well with the mechanical properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

PFG‐NMR measurement of self‐diffusion coefficients of long‐chain α‐olefins and their mixtures in semi‐crystalline polyethylene

The self‐diffusion coefficients of C6–C16 long‐chain α‐olefins and their mixtures in semi‐crystalline polyethylene were measured through the pulsed field gradient nuclear magnetic resonance (PFG‐NMR). The effects of chain length, polyethylene (PE) type, and co‐monomer type in PE on the diffusion coefficients were investigated. Moreover, the influence of halohydrocarbon, cycloalkanes, and arene solvents on the diffusion coefficients of C12 α‐olefin in PE was characterized. The results have demonstrated that the diffusion coefficient of the single‐component α‐olefin in PE decreases exponentially with the increase of the carbon number of α‐olefin, and the crystallinity and crystal morphology of PE play a more important role than the co‐monomer type in determining the diffusion coefficients of α‐olefins. In addition, the apparent diffusion coefficients were used to represent the diffusion behaviors of the α‐olefin mixtures in PE. Owing to the presence of other hydrocarbon solvents, namely trichloromethane, cyclohexane, and benzene, the diffusion coefficients of C12 long‐chain α‐olefin in PE are significantly enhanced, and such promoting effect of the hydrocarbon solvents in polyolefin elastomer (POE) is much stronger than those in high‐density polyethylene (HDPE) and linear low‐density polyethylene (LLDPE). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44143.     

Enhanced toughness and strength of poly (d‐lactide) by stereocomplexation with 5‐arm poly (l‐lactide)

The enhancement of mechanical properties were achieved by solution blending of poly(d ‐lactide) (PDLA) and 5‐arm poly(l ‐lactide) (5‐arm PLLA). Differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD) results indicated almost complete stereocomplex could be obtained when 5‐arm PLLA exceeded 30wt %. Tensile test results showed that the addition of 5‐arm PLLA in linear PDLA gave dramatically improvement both on tensile strength and elongation at break, which generally could not be increased simultaneously. Furthermore, this work transformed PDLA from brittle polymer into tough and flexible materials. The mechanism was proposed based on the TEM results: the stereocomplex crystallites formed during solvent evaporation on the blends were small enough (100–200 nm), which played the role of physical crosslinking points and increased the interaction strength between PDLA and 5‐arm PLLA molecules, giving the blends high tensile strength and elongation at break. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42857.     

Properties of natural rubber filled with untreated and treated spent coffee grounds

This work studied the properties of spent coffee ground (SCG) filled natural rubber (NR). The SCG was initially characterized by various techniques, prior to being added into rubber. Results revealed that SCG had relatively large particle size with very low specific surface area. It is mainly composed of organic compounds (such as protein, fatty acid, cellulose, hemicellulose, and lignin) with small quantity of inorganic substances (oxides of potassium, silicon, magnesium, calcium, and phosphorous). The incorporation of SCG in NR gave relatively low reinforcement and tended to retard vulcanization due to the presence of hydroxyl groups on the SCG surface. In addition to untreated SCG, reinforcement of SCG treated by liquid epoxidized natural rubber (LENR) and bis ‐ ( 3‐ triethoxysilylpropyl) tetrasulfide (TESPT) was investigated. Improvement of rubber properties was observed when SCG surface was treated. Overall, TESPT‐treated SCG gave the rubber with the highest mechanical properties, followed by LENR‐treated SCG and untreated SCG, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46060.     

Determination of the minimum sample size for a reliable strength measurement of talc‐filled polypropylene fibers

Accurate determination of mechanical properties plays an important role to comment on improvement in the mechanical properties of particle‐filled PP fibers. However, the existing standards are not totally suitable for reliable strength determination of particle‐filled PP fibers. In the framework of this study, microsized talc particle‐filled PP fibers were produced with different talc ratio and tensile strength measurements were performed with various gage lengths. Statistical Akaike Information Criterion analysis shows that strength distribution of talc‐filled PP fibers is best characterized by Weibull distribution function. It is reported that, the gage length has almost no influence of Weibull parameters of pure PP fibers while strong effects on Weibull parameters of talc‐filled PP fibers. It is shown that if the tensile strength of talc‐filled PP fibers is to be measured, at least 50 samples, which is more than value suggested by existing standard, should be used for a reliable determination of Weibull parameters. Therefore, the main aim of this study is to question the feasibility of minimum sample size suggested by the existing ASTM D3822 standard for reliable strength measurement of talc filled PP fibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44083.     

Effect of high‐energy ball milling on the structure and mechanical properties of ultra‐high molecular weight polyethylene

The structure and properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) powder after severe deformation processing in a planetary ball mill were studied by means of scanning electron microscopy, differential scanning calorimetry, and X‐ray analysis. We found that the severe deformation processing of UHMWPE changed the morphology of the powder and caused amorphization and partial changes in the structure of the crystalline phase. Monolithic samples were obtained from the pretreated polymer with a hot‐pressing method in a wide range of temperatures. The effect of preliminary deformation processing on the mechanical properties of UHMWPE was studied. It was revealed that during monolitization in its melting temperature range, the mechanical properties of the powder increased, whereas the percentage elongation decreased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2971–2977, 2013     

Structure–property relationships in photopolymerizable polymer networks: Effect of composition on the crosslinked structure and resulting thermomechanical properties of a (meth)acrylate‐based system

Photoinitiated polymer networks were formed by copolymerization of tert‐butyl acrylate with di(ethylene glycol) dimethacrylate (DEGDMA) or poly(ethylene glycol) dimethacrylate (PEGDMA). The degree of crosslinking was systematically varied by modifying the weight fraction and molecular weight of the dimethacrylate crosslinking agent. An increase in effective crosslink density with increasing crosslinking agent concentrations was confirmed by decreasing equilibrium swelling ratios (q) and increasing rubbery moduli (E_R). Glass transition temperatures (T_g) varied from ?22 to 124°C, increasing with increasing DEGDMA content and decreasing with increasing PEGDMA content. Tensile deformation behavior (at T_g) ranged from an elastomeric‐like large‐strain response for lightly crosslinked materials to a small‐strain brittle response for highly crosslinked networks. At low crosslinking levels, the strain‐to‐failure of the network polymers decreased quickly with increasing crosslinking agent concentration. The stress at failure demonstrated a more complex relationship with crosslinking agent concentration. The effect of composition on network structure and resulting properties (q, E_R, strain‐to‐failure) decreased as the crosslinking agent concentration increased. The results reveal trade‐offs in T_g, E_R, strain‐to‐failure, and failure stress with composition and network structure, and are discussed in light of the wide range of potential applications suggested in the literature for (meth)acrylate‐based photopolymerizable polymer networks including biomaterials and shape‐memory polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Strontium(II) ion uptake on poly(N‐vinyl imidazole)‐based hydrogels

In this article, we report on the extraction of Sr(II) ions from aqueous solution with a series of poly(N‐vinyl imidazole)‐based hydrogels. The hydrogels were synthesized by the crosslinking of N‐vinyl imidazole with four different crosslinkers with γ rays as initiators. The well‐characterized hydrogels were used as Sr(II) sorbents. Sr(II) uptake was determined with a colorimetric method with Rose Bengal anionic dye. Scanning electron microscopy–energy‐dispersive spectroscopy analysis of the Sr(II)‐loaded polymers was recorded to ascertain the uptake of Sr(II) ions. The experimental adsorption values were analyzed with the Freundlich and Temkin equations, and the kinetics of adsorption were investigated with a pseudo‐second‐order sorption kinetic model. The results show that the equilibrium data fit well in the Freundlich isotherm and followed a pseudo‐second‐order kinetic model. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Structure and property of tetrafluoroethylene‐propylene elastomer‐OVPOSS composites

Tetrafluoroethylene‐propylene elastomer‐octavinyl‐polyhedral oligomeric silsesquioxane (TFE/P‐OVPOSS) composites containing various percentages of OVPOSS are prepared via room temperature milling and heat vulcanization at 170°C. The composites are characterized by FTIR, ¹³C‐NMR, ²⁹Si‐NMR, XRD, DSC, SEM, tensile test, DMA, and TGA. The crosslink bond formation between TFE/P and OVPOSS conforms to the structural characterization of the composites. The OVPOSS cages aggregate when the OVPOSS dosage is more than 6 as observed from the XRD curves and SEM images. The swelling test shows that the experimental crosslink density is lower than the calculated crosslink density, indicating that not all reacted vinyl groups are converted into crosslink bonds. Meanwhile, the incorporation of OVPOSS significantly enhances the mechanical property and elevates the glass temperature of the composites. However, the thermal property is only improved slightly. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1281‐1288, 2013     

Diffusion mechanism of byproducts resulting from the peroxide crosslinking of polyethylene

In this study, a polyethylene grade used for applications in the insulation of energy cables was crosslinked by the peroxide crosslinking route. The impact of dicumyl peroxide (DCP) crosslinking on the polymer microstructure was studied. The different byproducts formed during the crosslinking reaction [acetophenone, α‐cumyl alcohol, and α‐methyl styrene (aMS)] were identified and quantified. Another molecule, 2,4‐diphenyl‐4‐methyl‐1‐pentene, regarded as an aMS dimer, was detected for the first time. Some amounts of residual DCP were also detected. A detailed study of the diffusion mechanism of each byproduct under different desorption conditions (e.g., samples exposed to vacuum or atmospheric conditions) and temperatures was performed. The diffusion coefficient values were determined and are discussed as a function of the desorption conditions and byproduct characteristics. Through this study, essential diffusion parameters were provided as a first step for further modeling development to allow the definition of optimized desorption conditions for a large range of sample geometries and thicknesses. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44525.     

Shape‐memory behavior of high‐strength amorphous thermoplastic poly(para‐phenylene)

The purpose of this study was to investigate the shape‐memory behavior of poly(para‐phenylene) (PPP) under varying programming temperatures, relaxation times, and recovery conditions. PPP is an inherently stiff and strong aromatic thermoplastic, not previously investigated for use as a shape‐memory material. Initial characterization of PPP focused on the storage and relaxation moduli for PPP at various frequencies and temperatures, which were used to develop continuous master curves for PPP using time–temperature superposition (TTS). Shape‐memory testing involved programming PPP samples to 50% tensile strain at temperatures ranging from 155°C to 205°C, with varying relaxation holds times before cooling and storage. Shape‐recovery behavior ranged from nearly complete deformation recovery to poor recovery, depending heavily on the thermal and temporal conditions during programming. Straining for extended relaxation times and elevated temperatures significantly decreased the recoverable deformation in PPP during shape‐memory recovery. However, PPP was shown to have nearly identical full recovery profiles when programmed with decreased and equivalent relaxation times, illustrating the application of TTS in programming of the shape‐memory effect in PPP. The decreased shape recovery at extended relaxation times was attributed to time‐dependent visco‐plastic effects in the polymer becoming significant at longer time‐scales associated with the melt/flow regime of the master curve. Under constrained‐recovery, recoverable deformation in PPP was observed to have an exponentially decreasing relationship to the bias stress. This study demonstrated the effective use of PPP as a shape‐memory polymer (SMP) both in mechanical behavior as well as in application. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42903.     

Ductile tear behavior of multilayered polypropylene homopolymer/ethylene 1‐octene copolymer sheets

The tear resistance of the polypropylene homopolymer (HPP)/ethylene 1‐octene copolymer (POE) alternating multilayered sheets, which were prepared through multilayered coextrusion, was evaluated. Polarized optical microscope (POM) photographs revealed that HPP and POE layers aligned alternately vertical to the interfaces and continuously parallel to the extrusion direction. Tear results demonstrated the conventional blends had less tear‐resistant than the multilayered samples. Large plastic deformation of HPP layer occurred in the multilayered structure during the stable crack growth, causing the tear energy to increase with the number of layers increasing. The measurements of PCMW2D IR and WAXD revealed that the large plastic deformation had a direct relationship with the crystal structure and termination of micro‐cracks by interface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43298.     

Electromagnetic interference shielding effectiveness of graphite‐filled polypropylene and poly(ether imide) based composites

The electromagnetic interference shielding characteristics of polypropylene (PP) and poly(ether imide) (PEI) filled with synthetic graphite composites were studied. The thermal properties were characterized by differential scanning calorimetry and thermogravimetric analysis, whereas the morphologies of the composites were studied by scanning electron microscopy. The viscosity measurements were studied by advance rheometry. The measurements of shielding effectiveness (SE) were carried out in the frequency range 8–12 GHz (X‐band range). The return loss and loss due to absorption were also measured as a function of frequency in the X‐band range. It was observed that the SE of the composites was frequency dependent, and it increased with increasing frequency. The SE also increased with increasing filler loading. The PEI‐based composites showed a higher SE compared to that of the PP‐based composites. The correlation between SE and the conductivity of the various composites is also discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Interaction and properties of epoxy‐amine system modified with poly(phthalazinone ether nitrile ketone)

An epoxy based on the tetraglycidyl 4,4′‐diaminodiphenyl‐ methane (TGDDM)/bisphenol A type novolac(F‐51) cured with 4,4′‐diaminidiphenysulfone (DDS) has been modified with Poly (phthalazinone ether nitrile ketone)(PPENK). The interaction between the PPENK and epoxy resin have been investigated by differential scanning calorimetry (DSC), FT‐IR, and dynamic mechanical analysis (DMA). The thermal and mechanical properties were characterized by thermogravimetric analysis (TGA), thermomechanical analysis (TMA), flexural, impact strength, and the critical stress intensity factor tests. The results showed that a large number of physical crosslinks formed by intermolecular and intramolecular hydrogen bonding indeed existed in the TGDDM/F‐51/PPENK blends. These interactions gave good compatibility between PPENK and epoxy resin. So that any phase separation had not been detected by DMA and scanning electron microscope (SEM). Beyond that the interaction could also be a benefit to the thermal and mechanical properties. Compared with the neat epoxy resin, the critical stress intensity factor values reached the maximum at 10‐phr PPENK, as well as the impact strength. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42938.     

Photosensitive polynorbornene based dielectric. I. Structure–property relationships

In the microelectronics industry, the drive for increasing device speed, level of functionality and shrinking size has placed significant demands on the performance characteristics of polymer dielectrics. In this study, a negative acting, photodefinable dielectric formulation based on a copolymer of decylnorborne (decylNB) and epoxynorbornene (AGENB) was investigated for use in electronics packaging. The structure–property relations of this copolymer were investigated. Copolymer composition and processing conditions were shown to significantly affect the properties of the final polymer films. A lower content of AGENB results in lower moisture absorption, dielectric constant, modulus and residual stress, but it compromises multilayer capability. High crosslink density lowers the dielectric constant but increases the modulus and residual stress. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3023–3030, 2004     

Molecular,rheological, and thermal study of long‐chain branched polypropylene obtained by esterification of anhydride grafted polypropylene

Long‐chain branched polypropylene was prepared using reaction in the molten state in the presence of glycerol and a linear polypropylene functionalized with maleic anhydride (PPg). The concentration of glycerol in the melt was varied in the range from 0.1 to 5 wt % to obtain different levels of branching. FTIR spectroscopy results indicate that the OH groups of glycerol react with the anhydrides on the PPg chains giving place to ester groups. The presence of long‐chain branches in the molecular structure of PPg was confirmed using multiple‐detection size‐exclusion chromatography and rheology. These techniques demonstrate that the level of branching increases with glycerol concentration and that the modification of PPg produces materials with a bimodal distribution of polymer species. Moreover, some of the highly modified materials display gel‐like behavior. The materials also display thermo‐rheological complexity and enhanced activation energy at low frequencies. The crystallization study shows that both the anhydride groups in PPg and the LCBs have opposite nucleating effects. PPg presents the largest activation energy of crystallization and its value decreases with the concentration of glycerol for a given level of crystallization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40357.