Vi‐PDMS incorporated with protein‐based coatings designed for permeability‐enhanced applications

Functional polydimethylsiloxanes containing vinyl groups (Vi‐PDMS) were used for silicone‐based organic polymers in composites and adhesive formulations. Poly(butyl acrylate/methyl methacrylate/vinyl silicone oil)/casein–caprolactam [P(BA‐MMA‐Vi‐PDMS)/CA‐CPL] nanoparticles were prepared via emulsifier‐free polymerization. The well‐defined core–shell structure of P(BA‐MMA‐Vi‐PDMS)/CA‐CPL nanoparticles was verified by transmission electron microscopy. The results of scanning electron microscopy and contact angle measurements proved that the as‐obtained coatings exhibited porous and hydrophobic properties, which were helpful for superior water vapor permeability. By comparing the appearance of the coatings before and after adhesion analysis, the excellent adhesion strength was proved to be dominated by Vi‐PDMS. The relationship between interface morphology and properties of the resultant coatings was investigated in detail. The nucleation mechanism for this soap‐free emulsion synthesis was also proposed accordingly. These results could help in designing coatings with better surface properties and wider application. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46501.     

Co‐extruded polymeric films for gas separation membranes

In recent years, gas separation has become an important step in many production process streams and part of final products. Through the use of melt co‐extrusion and subsequent orientation methods, gas separation membranes were produced entirely without the use of solvents, upon which current methods are highly dependent. Symmetric three layer membranes were produced using poly(ether‐block‐amide) (PEBA) copolymers, which serve as a selective material that exhibits a high CO₂ permeability relative to O₂. Thin layers of PEBA are supported by a polypropylene (PP) layer that is made porous through the use of two methods: (1) inorganic fillers or (2) crystal phase transformation. Two membrane systems, PEBA/(PP + CaCO₃) and PEBA/β‐PP, maintained a high CO₂/O₂ selectivity while exhibiting reduced permeability. Incorporation of an annealing step either before or after orientation improves the membrane gas flux by 50 to 100%. The improvement in gas flux was a result of either elimination of strain induced crystallinity, which increases the selective layer permeability, or improvement of the PP crystal structure, which may increase pore size in the porous support layer. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39765.     

Peel‐strength behavior of bilayer thermal‐sprayed polymer coatings

We prepared various bilayer polymer coatings of ethylene methacrylic acid (EMAA) copolymer and ionomer by the thermal‐spray process under a range of preheat temperatures (PTs) to investigate their ability to be repaired. The thermal properties, crystallinity, microstructure, and interface strength of the coatings were investigated with differential scanning calorimetry, X‐ray diffraction, scanning electron microscopy, and mechanical testing. Processing parameters influenced the final morphological structure of the coatings. The crystallinity of the coatings increased with a higher final temperature, whereas the coating density decreased. The decrease in density was attributed to the appearance of bubbles, 250 μm in size, formed in the coatings during the spray process. For the monolayer coating of polymer on a metal substrate, a higher PT produced a greater contact area of the coating to the substrate. The adhesion of EMAA ionomer to steel was always lower than that of EMAA copolymer to steel. This may have been largely due to the interfacial adhesion between the polymer and steel being dominated by strong secondary bond interactions. Experimental results also indicate that the peel strength between polymers was at least twofold stronger than that between the polymer and the steel substrate for PTs greater than 100°C. The mixed bilayer coating of ionomer on copolymer produced the highest peel strength. The interface between the plastic layers was clearly visible under the scanning electron microscope at lower PTs, becoming more diffuse with an increase in PT. On the basis of these observations, the adhesion mechanism between polymers was explained by the formation of welding points. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 214–226, 2003     

Matrix effect of mixed‐matrix membrane containing CO2‐selective MOFs

Facilitated mixed‐matrix membranes (MMMs) containing Cu‐metal organic frameworks (Cu‐MOFs) with high CO₂ selectivity on an asymmetric polysulfone support were fabricated and examined the effect of gas separation performance using different matrices. An amorphous poly(2‐ethyl‐2‐oxazoline) (POZ) and semicrystalline poly(amide‐6‐b‐ethylene oxide) (PEBAX^®MH 1657) block copolymer were chosen as the polymeric matrix and the effect of the matrix on CO₂ separation for MMMs containing Cu‐MOFs was investigated. The interaction of CO₂ in different matrix was investigated theoretically using the density functional theory method, and it was found that the amide segment in PEBAX would contribute more to the CO₂ solubility than ether segment. The morphological changes were investigated by differential scanning calorimetry, field emission scanning electron microscope and X‐ray diffractometer. The ideal selectivity of CO₂/N₂ was enhanced significantly with the addition of a Cu‐MOF, and the values are higher in the Cu‐MOF/PEBAX MMM compared with that in a POZ based asymmetric MMM. Improvement in the CO₂/N₂ selectivity of a Cu‐MOF/PEBAX MMM was achieved via facilitated transport by the CO₂‐selective Cu‐MOFs due to both their high adsorption selectivity of CO₂ over N₂ and the decreased crystallinity of PEBAX due to the presence of the Cu‐MOFs, which would provide a synergic effect on the CO₂ separation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42853.     

Effect of solid‐state shear milling on structure and properties of HDPE/UHMWPE blends

The structure and properties of HDPE/UHMWPE blends prepared through a pan‐milling reactor in solid state at ambient temperature were compared with the blends made by melt mixing. The changes of structure and properties of the blends were investigated by FTIR, melt flow index, mechanical properties, dynamic rheological measurement, DSC, and WAXD. DSC measurement illustrated that after pan‐milling treatment, the half‐width of the melting temperature became smaller. The more content of UHMWPE added in the blend, the more evident change was observed. Combined with the dynamic rheological analysis, it was proved that, the pan‐milling treatment can improve the compatibility of the HDPE/UHMWPE blends. X‐ray diffraction analysis showed that after pan‐milling treatment some ordered structure could be induced, but after heat treatment, the induced crystalline structure disappeared. The tensile properties of pan‐milled HDPE/UHMWPE blends also achieved improvement after pan milling treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39916.     

Two‐stage drawing process to prepare high‐strength and porous ultrahigh‐molecular‐weight polyethylene fibers: Cold drawing and hot drawing

High‐strength and porous ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers have been prepared through a two‐stage drawing process. Combined with tensile testing, scanning electron microscopy, and small‐angle X‐ray scattering, the mechanical properties, porosity, and microstructural evolution of the UHMWPE fibers were investigated. The first‐stage cold drawing of the gel‐spun fibers and subsequent extraction process produced fibers with oriented lamellae stacks on the surface and plentiful voids inside but with poor mechanical properties. The second‐stage hot drawing of the extracted fibers significantly improved the mechanical properties of the porous fibers because of the formation of lamellar backbone networks on the surface and microfibrillar networks interwoven inside to support the voids. With various processing conditions, the optimized mechanical properties and porosity of the prepared UHMWPE fibers were obtained a tensile strength of 1.31 GPa, a modulus of 10.1 GPa, and a porosity of 35%. In addition, a molecular schematic diagram is proposed to describe structural development under two‐stage drawing, including void formation and lamellar evolution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42823.     

Preparation of novel CNSL‐based urethane polyol via nonisocyanate route: Curing with melamine‐formaldehyde resin and structure–property relationship

In this study, we report preparation of a novel cashew nut shell liquid (CNSL)‐based polyol bearing urethane groups. The urethane group in the polyol was induced via isocyanate free route from the reaction of cyclic carbonate with primary amine. The polyol was characterized by determination of hydroxyl number, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and so forth. The polyol was then used as coating component and cured with hexamethoxy methylene melamine (HMMM). Another CNSL‐based polyol without urethane moiety from our earlier reported work was used for preparation of coating for comparative study to determine the effect of urethane group on the coating properties. The coating formulations based on these two polyols were cured with variable amounts of HMMM hardener to optimize coating properties. All the coatings were evaluated for mechanical properties such as adhesion, flexibility, pencil and scratch hardness, impact resistance, pull‐off, and adhesion. The optimized coatings were also evaluated for chemical and thermal properties. It was observed that the urethane containing polyol resulted in better adhesion to the metal substrate at higher quantity of HMMM hardener compared to the other polyol providing significant improvement in various coating properties. The final coating properties were also compared with the acrylic polyurethane coatings. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41391.     

Preparation,structure, and properties of end‐functionalized miktoarms star‐shaped polybutadiene–sn–poly(styrene–butadiene) rubber

Two miktoarm star‐shaped rubbers with large‐volume functional groups of 1,1‐diphenylhexyl at the ends of arms (DMS–PB–SBR) and one miktoarm star‐shaped rubber with n‐butyl groups at the ends of arms (BMS–PB–SBR) were prepared by 1,1‐diphenylhexyllithium (DPHLi) and n‐butyl lithium as initiators, respectively. The molecular structures and morphological properties of the three rubbers (MS–PB–SBR) were studied and compared with those acquired from the blend consisting of star‐shaped solution‐polymerized butadiene styrene rubber (S‐SSBR) and butadiene rubber (PBR) prepared by ourselves. The results showed that MS–PB–SBR exhibited a more uniform distribution of PBR phase and a smaller phase size of PBR than that of S‐SSBR/PBR blend. It is found that MS–PB–SBR composites filled with CB showed the lower Payne effect than that of S‐SSBR/PBR/CB composite, suggesting that the MS–PB–SBR/CB composite (particularly the DMS–PB–SBR/CB composites) would possess excellent mechanical properties, high wet‐skid resistance, and low rolling resistance. For the studied MS–PB–SBR systems, the contribution of large‐volume functional groups at the end of PBR molecular chains to decrease the rolling resistance was larger than that of Sn coupling effect. It is envisioned that the miktoarm star‐shaped rubbers with 1,1‐diphenylhexyl groups at the molecular ends would be useful for making treads of green tires. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40002.     

Morphological and electromechanical studies of fibers coated with electrically conductive polymer

Electrically conductive fibers have been prepared by polymerization of pyrrole on surfaces of commercial polymer fibers. Thickness and morphology of the conducting thin film on the surface of the fibers were examined by scanning probe microscopy, indicating a strong dependence of the substrate's nature, in addition to the processing conditions. Electromechanical property was investigated by an electromechanical testing system, showing that a smooth and uniform coating and the matched mechanical properties will lead to a satisfied performance of conductive fiber sensors. The difference in the behavior of two types of composite fibers was investigated by scanning electron microscopy in situ observations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1844–1854, 2005     

Control of structure and tack properties of acrylic pressure‐sensitive adhesives designed by a polymerization process

Free radical emulsion polymerization of methyl methacrylate (MMA) and 2‐ethylhexyl acrylate (EHA) results in the synthesis of pressure‐sensitive adhesives (PSAs) with good tack properties. Management of both the copolymer composition and the polymerization process allows one to control the behavior of the PSA. Semicontinuous (SC) processes create polymer particles whose instantaneous composition is close to that of the feed particle The SC Mixture process (continuous feeding with comonomer blends) affords nearly homogeneous latex particles and PSA films. The SC Gradient process (separate feedings at inversely varying rates) affords heterogeneous particles and films. The Batch process leads to somewhat heterogeneous films, but the hard (MMA‐rich) microdomains are made compatible with their soft (EHA‐rich) matrix because of the assumed formation of tapered‐type copolymers. Tack measurements indicate the importance of the particle and film structures. Too much hardness or softness leads to unacceptable lacks of adhesion and cohesion, respectively. Homogeneous structures prove adequate, but their tack properties collapse with rising temperature. Heterogeneous structures, with extensive phase segregation, prove unsatisfactory because they lack adhesion and cohesion. Finally, the association of well‐balanced composition and compatible heterogeneity is the criterion for suitable PSA behavior. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2749–2756, 2003     

Facile fabrication of polyimide foam sheets with millimeter thickness: Processing,morphology, and properties

A series of polyimide foam sheets (PIFSs) with thickness of 0.5 mm using 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 3,4′‐oxydianiline (3,4′‐ODA), and polyaryl polymethylene isocyanate (PAPI) as main materials were first fabricated by liquid foaming and compression molding technology. The effects of different PAPI contents and 3,4′‐ODA contents on the structures and properties of PIFSs were investigated. The results indicated that PIFSs exhibited a structure that front surface displayed closed cells made of damaged cell walls and membranes, while internal cells were open, and elliptic vacancies were flatted in the thickness direction from the cross section. The average cellular diameter increased with increasing PAPI loading. In addition, the introduction of 3,4′‐ODA increased the average cell size of PIFSs. Further, PIFSs had density of 0.087–0.239 g/cm³, elongation at break of 3.75–8.01% and tensile toughness of 3.46 × 10^?2?13.87 × 10^?2 J/cm³. Notably, they exhibited higher tensile strength of 1.89–5.42 MPa and lower thermal conductivity of 14.727–19.25 mW/m ?K at 24°C, compared to the polyimide foams reported earlier. The sound absorption coefficients (α) of samples with different PAPI contents increased and then decreased with increasing PAPI content. At low frequencies, a certain content of 3,4′‐ ODA allowed an improvement of the acoustical behavior of PIFSs, and the α increased and then decreased with increasing density. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39881.     

Enhancing particle erosion resistance of glass‐reinforced polymeric composites using carbon nanofiber‐based nanopaper coatings

Sand erosion may cause severe damage of blades in wind turbine and helicopter blades as well as many surface components of airplanes. In this study, thin nanopapers made of carbon nanofibers (CNFs) are used to enhance the resistance of solid particle erosion of glass fiber (GF)/wind epoxy composites. Finite element computer simulations are used to elucidate the underlying mechanisms. The much higher particle erosion resistance of nanopapers compared to GF‐reinforced epoxy composites is attributed to the high strength of CNFs and their nanoscale structure. The excellent performance in particle erosion resistance makes the CNF‐based nanopaper a prospective protective coating material for the turbine blades in the wind energy industry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of the casting solvent on the free‐volume characteristics and gas permeability of poly[1‐(trimethylsilyl)‐1‐propyne] membranes

The effect of the casting solvent on the structure of poly[1‐(trimethylsilyl)‐1‐propyne] (PTMSP) membranes was investigated experimentally. The PTMSP membranes were cast from solutions of cyclohexane, toluene, and tetrahydrofuran; the membranes were characterized by the positron annihilation lifetime spectroscopy (PALS) technique and by gas‐permeation measurements of O₂, N₂, and CO₂. The decay curves from the positron annihilation lifetime spectroscopy gave the best fit when two long‐life components (τ₃ and τ₄, τ₃ < τ₄) were employed. This suggests that two types of free volume existed in the PTMSP membranes. The size and number density of τ₄, which was characteristic for PTMSP, decreased in the following order of the casting solvents: cyclohexane > toluene > tetrahydrofuran. The order was consistent with the order of gas permeability. A good correlation was observed between the permeability and the structural parameter that denoted the free‐volume size and the number density of τ₄. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 497–501, 2003     

Structure and properties of AlSi/polyester coating

Powder coatings, which are formed by plasma spray technique, are being used in industrial applications. Resistance of plastics and their based composite materials to chemicals, solvents, atmospheric conditions, and high impact strength even at low service temperature increases the importance of plastic and plastic based coating applications. In this study, aluminum silicon based polyester (AlSi/polyester) coating was applied by plasma spraying technique with and without intermediate bond layer coat (NiAl). The effect of coating thickness, intermediate bond layer coat, and plasma spraying parameters on bond strength of coating were studied experimentally. The bond strengths of the coatings were determined according to the ASTM C‐633–79. Microstructures of the coating were examined by optic microscopy and scanning electron microscopy (SEM), respectively. Obtained results indicated that plasma spraying current rate, coating thickness, and spraying distance were important factors on bond strength of coating. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2437–2444, 2004     

Acrylamide‐b‐N‐isopropylacrylamide block copolymers: Synthesis by atomic transfer radical polymerization in water and the effect of the hydrophilic–hydrophobic ratio on the solution properties

A series of block copolymers of acrylamide and N‐isopropylacrylamide (NIPAM) characterized by different ratios between the length of the two blocks have been prepared through atomic transfer radical polymerization in water at room temperature. The solution properties of the block copolymers were correlated to their chemical structure. The effect of the hydrophilic/hydrophobic balance on the critical micelle concentration (CMC) was investigated. The CMC increases at higher values for the solubility parameter, thus indicating a clear relationship between these two variables. In addition, the solution rheology (in water) of the block copolymers was studied to identify the effect of the chemical structure on the thermo‐responsiveness of the solutions. An increase in the length of the PNIPAM block leads to a more pronounced increase in the solution viscosity. This is discussed in the general frame of hydrophobic interactions strength. The prepared polymers are in principle suitable for applications in many fields, particularly in enhanced oil recovery. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39785.     

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     

Effects of equal‐channel,multiple‐angular extrusion on the physical and mechanical properties of glassy polymers

Through the examples of polycarbonate and poly(methyl acrylate), the evolution of the structure and properties of glassy polymers processed by equal‐channel multiple‐angular extrusion (ECMAE) were studied. It was demonstrated that ECMAE allowed the substantial improvement of the set of strain–strength characteristics of these materials, regardless of the direction of loading applied. With the use of the data from scanning electron microscopy, differential scanning calorimetry, and dilatometry, we found that the simultaneous growth in the strength, plasticity, and impact resistance was related to the formation of a net of biaxially oriented polymeric chains, the decrease in the free volume, and the reinforcement of intermolecular interaction. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42180.     

Superporous collagen‐sericin scaffolds

Superporous materials based on two proteins, collagen and sericin were synthesized by freeze‐drying considering various ratios between the two proteins. To evaluate the influence of sericin content on the structure/properties relationship, the obtained scaffolds were further characterized using spectroscopic analysis, thermal, and mechanical techniques. Scanning electron microscopy was used to investigate the morphological structure of the scaffolds and the swelling properties as well as the stability of the scaffolds were also assessed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhanced crystallization of poly(L‐lactide‐co‐ε‐caprolactone) in the presence of water

Poly(L ‐lactide‐co‐ε‐caprolactone) [P(LLA‐CL)], which is used in biodegradable biomedical materials such as drug‐delivery systems, surgical sutures, orthopedics, and scaffolds for tissue engineering, has been reported to crystallize upon storage in a dry state even at room temperature; this results in rapid changes in the mechanical properties. In biomedical applications, P(LLA‐CL) is used in the presence of water. This study investigated the effects of water on the crystallization of P(LLA‐CL) at 37°C in phosphate buffered solution, which was anticipated to alter its mechanical properties and hydrolytic degradation behavior. Surprisingly, the crystallinity of P(LLA‐CL) in the presence of water rapidly increased in 6–12 h and then slowly increased up to 120 h. The period of time for the initial rapid crystallization increase in the presence of water was much shorter than that in the absence of water. The obtained information would be useful for the selection, preparation, and use of P(LLA‐CL) in various biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of recycling and contamination on structure and transport properties of polypropylene

In this work the effect of three processing cycles on the physical properties of polypropylene (PP) was studied and related to the changes in the structure (molecular weight, molecular weight distribution, morphology) occurring during recycling. In order to simulate both the use and the recycling process of PP in the laboratory, PP pellets were contaminated with three model substances and submitted to three cycles of processing by injection molding. The bars for testing were produced from virgin and recycled polymers. The amount of degradation occurring during the reprocessing was estimated by means of viscosity and gel permeation chromatography measurements. Differential scanning calorimetry and scanning electron microscopy analyses were performed to investigate the crystallization behavior and the morphology of virgin and recycled PP. In order to obtain information on the structural organization and mobility of the amorphous phase, a dynamic mechanical thermal analysis and measurements of the transport properties were carried out. The results obtained were attributed to the different structural organization of the bars in relation to the number of processing cycles and contamination. Part of the work was focused on the recyclability of PP for food packaging applications, considering the residual contamination and migrational behavior after repeated processing cycles. In particular, the relationships existing between reprocessing, the residual amounts of contaminants, and the migrational behavior were investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1768–1778, 2003