Small diameter tubular structure design using solvent‐free textile techniques

The aim of research was to elaborate the non‐biodegradable (made of polypropylene (PP)) and resorbable (made of polylactide (PLA)) tubular fibrous structures for the reconstruction of the vascular vessels. For the mentioned structures design, nonconventional manufacturing techniques such as melt blown, melt electrospinning, and melt electroblowing were used. Three techniques were chosen as methods allowing on the fibrous structures manufacture containing fibers in nano‐ or submicro‐size diameter. Other advantages of free‐solvent technique use is the reduction in the clinical adverse events associated with solvent resided in the fibrous structure during the fabrication. The tubular fibrous structures of PP and PLA using above‐mentioned techniques were designed. In first stage, the analysis of the processing parameters influence on the nonbiodegradable and biodegradable tubular structures fiber diameter was performed. Subsequently, the validation step was the analysis of the influence of processing parameters on PP and PLA structural properties for each manufacturing techniques was investigated. The research results confirmed the ability of the tubular structures manufacture with various fiber diameter depending on the applied technique and processing parameters. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40147.     

Effect of solution properties on nanofibrous structure of electrospun poly(lactic‐co‐glycolic acid)

Electrospinning of poly(lactic‐co‐glycolic acid) (PLGA) in chloroform or 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) was investigated, focusing on its solution parameters, to develop nonwoven biodegradable nanofibrous structures for tissue engineering. PLGA nanofibers were obtained by electrospinning of 15 wt % PLGA solution and the resulting average fiber diameters were varied with the range of 270–760 nm, depending on solution property. When small amounts of benzyl triethylammonium chloride (BTEAC) was added to the PLGA/chloroform solution, the average diameter was decreased from 760 to 450 nm and the fibers were densely amounted in a straight shape. In addition, the average fiber diameter (270 nm) of nanofibers electrospun from polar HFIP solvent was much smaller than that (760 nm) of nanofibers electrospun from nonpolar chloroform solvent. Therefore, it could be concluded that conductivity or dielectric constant of the PLGA solution was a major parameter affecting the morphology and diameter of the electrospun PLGA fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1214–1221, 2006     

Melt‐electrospun fibers obtained from polypropylene/poly(ethylene‐co‐vinyl alcohol)/polypropylene three‐layer films

Production of polypropylene (PP) nanofibers below 1 μm in average diameter is difficult with conventional melt‐spinning. A nozzle‐free melt‐type electrospinning (M‐ESP) system with a line‐like CO₂ laser beam melting device were used to produce PP nanofibers. To achieve the purpose, core [poly(ethylene‐co‐vinyl alcohol) (EVOH)]–clad (PP) nanofibers (average diameter, 0.88 μm) were fabricated from PP/EVOH/PP three‐layer films using the M‐ESP. The core–clad structure was formed by a wrapping phenomenon caused by the difference in the melt flow rates (MFRs) of PP and EVOH melts. Hollow PP nanofibers were obtained from the core–clad nanofibers by extraction of EVOH. Nanofiber diameter and hollow wall thickness could be altered by changing the MFR of the PP melt. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46393.     

In vitro degradation and drug‐release behavior of electrospun,fibrous webs of poly(lactic‐co‐glycolic acid)

Ultrafine fibrous webs of poly(lactide‐co‐glycolic acid) (PLGA) containing the bactericidal antibiotic drug rifampin were prepared by electrospinning, and their properties were investigated for wound‐dressing applications. Because PLGA is a biodegradable and biocompatible polymer, it is one of the best materials for the preparation of wound‐dressing substrates. Through this investigation of PLGA/rifampin electrospun webs, we found that the in vitro degradation reached approximately 60% in 10 days, and the drug release from the webs showed a fast and constant profile suitable for wound‐dressing applications. Also, we observed that both the web‐degradation rate and the drug‐release rate increased as the drug concentration in the PLGA/rifampin electrospun webs and the content level of glycolide units in the PLGA polymer matrix increased. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

静电纺PLGA管状支架的构建及其生物力学性能

以具有良好生物相容性、生物可降解性的聚丙交乙交酯(PLGA)为原料,以高速旋转的滚轴为收集装置,通过静电纺丝法,制备PLGA管状支架(d=6mm)。研究不同工艺及乙醇处理对PLGA管状支架形貌结构、微细结构和生物力学性能的影响。结果表明:当纺丝液质量分数为7%,滚轴转速为1500r/min时,可制得纤维形貌规整、分布均匀,直径为(1660±218)nm,孔隙率为80.6%的PLGA管状支架;经乙醇处理后,其孔隙率减小,玻璃化温度和热分解温度提高,热稳定性增强;断裂强度、爆破强度及缝合强力均显著提高。     

Synthesis and structure control of l‐lactic acid–glycolic acid copolymer by homo‐copolymerization

A two‐step direct melt copolymerization process of l ‐lactic acid (L ‐LA)/glycolic acid (GA) was developed: poly(l ‐lactic acid) (PLLA) and poly(glycolic acid) (PGA) with different molecular weight was first synthesized respectively by binary catalyst (tin chloride/p‐toluenesulfonic or tin chloride); and then poly(l ‐lactic‐co‐glycolic acid) (b‐PLGA) was produced by melt polymerization of the as‐prepared PLLA and PGA, wherein the composition and chain structure of b‐PLGA copolymers could be controlled by the molecular weight of PLLA. The chain structure and thermal properties of copolymers were studied by Wide‐angle X‐ray diffraction, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. In comparison with the random PLGA (r‐PLGA) synthesized by one‐step direct melt polymerization, the average l ‐lactic blocks length (L_LA) in b‐PLGA was longer while the average glycolic blocks length (L_GA) in b‐PLGA was shorter which further resulted in the improved crystallinity and thermostability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41566.     

Water filtration properties of novel composite membranes combining solution electrospinning and needleless melt electrospinning methods

New composite polyvinyl alcohol (PVA)/polypropylene (PP) membranes were prepared by combining both solution electrospinning and melt electrospinning methods. Self‐designed and made needleless melt electrospinning device was used to fabricate PP membranes which acted as the support layer. PVA membrane on the surface was fabricated via solution electrospinning. The electrospun PVA/PP composite membranes were characterized by the pore size distribution, pure water flux, and rejection ratio, then compared with general composite membranes. Characterizations revealed that the fiber diameter of solution electrospun PVA membrane and melt electrospun PP membrane were 0.171 ± 0.027 and 2.24 ± 0.33 μm, respectively, and the average pore size was 0.832 μm and 27.29 μm, which was much smaller than the nonwoven membrane. The rejection ratio to the 500 nm particles of the PVA/PP composite membrane could reach more than 96%, which was much larger than that of the PVA/non‐woven substrate of 90%, and the melt electrospun PP membrane of 80%, and still maintained high permeate flux of 32,346 L/m²h under the pressure of 0.24 bar. This approach of compositing the solution electrospun membranes and melt electrospun membranes could be useful in designing novel microfiltration membrane owning both higher flux and higher rejection ratio. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41601.     

Polypropylene fibers fabricated via a needleless melt‐electrospinning device for marine oil‐spill cleanup

Ultrafine polypropylene (PP) fibers as oil sorbents were fabricated via a needleless melt‐electrospinning device and were characterized by scanning electron microscopy and contact‐angle analysis. PP fibers of various diameters and porosities were obtained by the manipulation of the applied electrical field. The effects of the fiber diameter and porosity on the oil‐sorption capacity and oil‐retention behavior were investigated. The experimental results demonstrate that for fiber diameter on the microscale, the porosity played a paramount role in determining the oil‐sorption capacities. The maximum oil‐sorption capacity of the resulting PP fibers with regard to motor oil and peanut oil were 129 and 80 g/g, respectively; these values were approximately six to seven times that of commercial PP nonwoven fabricated through the melt‐blown method. In addition, even after seven sorption/desorption cycles, the oil‐sorption capacity of the chosen sample was still maintained around 80 g/g, and above 97%, oil could be recovered. This indicated excellent reusability and recoverability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40080.     

Synthesis and processability into textile structures of radiopaque,biodegradable polyesters and poly(ester‐urethanes)

Radiopaque biodegradable polymers have been synthesized by ring‐opening polymerization of l /dl ‐lactide and caprolactone with the iodine‐containing starter molecule 2,2‐bis(hydroxymethyl)propane‐1,3‐diyl bis(2,3,5‐triiodobenzoate) followed by chain elongation with a diacid chloride or diisocyanates. The resulting polyesters and poly(ester‐urethanes) exhibited a radiopacity of 60?124% relative to an aluminium sample of the same thickness. The polymers were processed into monofilament fibres by melt‐spinning and into fibre meshes by electrospinning. All polymers were biodegradable in simulated body fluid medium under in vitro conditions and showed an excellent in vitro cytocompatibility even after several months of hydrolytic degradation. A current drawback is the relatively low tensile strength of the polymer monofilaments, which needs to be improved for applications as textile structures. Nevertheless, the new radiopaque and biodegradable polymers are promising candidates in fields of application where radiopacity of implants is an important parameter.     

Synthesis of phosphorus‐ and phenyl‐based ROMP polymers and investigation of their effects on the thermomechanical and flammability properties of a polypropylene–IFR system

In this study, we present an approach for the synthesis of novel phosphorous‐ or phenyl‐ containing polymers, 2_phenyl, 3_phospho, and 2_phenyl‐co‐3_phospho, derived from ring‐opening metathesis polymerization (ROMP), to reduce the flammability of polypropylene (PP). The composites were processed by melt‐blending ROMP polymers and octaphenyl–polyhedral oligomeric silsesquioxane with PP/intumescent flame retardant (IFR) compounds at different compositions. The composites were characterized by limiting oxygen index (LOI), UL‐94, and mechanical tests as well as thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The molecular structures of phosphorous‐ and phenyl‐containing polymers were proved by ¹H‐NMR, ¹³C‐NMR, and Fourier transform infrared spectroscopy. The online rheological measurements indicated that the addition of additives to the PP/IFR system increased the melt viscosity of the compounds regardless of the type. The DSC analysis showed that the addition of ROMP polymers to the PP/IFR system influenced the crystal perfection and degree of crystallization. TGA analysis of the composites revealed that the addition of ROMP polymers to PP/IFR compounds deteriorated the thermal stability as the amount of phosphorus increased in the matrix. Dynamic mechanical properties such as storage modulus (E′) and loss modulus (E″) of the composites were lowered by the addition of ROMP polymers. The LOI and UL‐94 rating of PP/IFR were enhanced by the addition of ROMP polymers. It was successfully demonstrated that the novel phosphorous‐ or phenyl‐containing polymers were highly potent additives in optimizing the flammability of PP composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45998.     

Syntheses of poly(lactic acid‐co‐glycolic acid) serial biodegradable polymer materials via direct melt polycondensation and their characterization

The optimal synthetic conditions of poly(lactic acid‐co‐glycolic acid) (PLGA) via melt copolycondensation directly from L ‐lactic acid (L ‐LA) and glycolic acid (GA) with a feed molar ratio of 50/50 are discussed; the important drug‐delivery carrier PLGA50/50 is used as a special example. With reaction conditions of 165°C and 70 Pa and with 0.5 wt % SnCl₂ as the catalyst, 10 h of polymerization gave the L ‐PLGA50/50 with the biggest intrinsic viscosity ([η]), 0.1993 dL/g. The optimal synthetic conditions were verified by the synthesis of D,L ‐PLGA50/50 with D,L ‐lactic acid (D,L ‐LA) instead of L ‐LA, but the biggest [η] was 0.2382 dL/g. Under the same synthetic conditions with L ‐LA and D,L ‐LA as starting materials, serial PLGA with different molar feed ratios, including 100/0, 90/10, 70/30, 50/50, 30/70, 10/90, and 0/100, were synthesized via simple and practical direct melt copolycondensation, and their solubilities were investigated. When the glycolic acid feed molar percentage was equal to or more than 70%, solubilities in tetrahydrofuran and CHCl₃ became worse, and some samples were even wholly insoluble. These biodegradable polymers were also systematically characterized with gel permeation chromatography, Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, differential scanning calorimetry, and X‐ray diffraction. PLGA synthesized from L ‐LA and D,L ‐LA had many differences in weight‐average molecular weight (M_w), glass‐transition temperature, crystallinity, and composition. When the molar feed ratio of LA to GA was 50/50, both the [η] and M_w values of D,L ‐PLGA were higher than those of L ‐PLGA. With D,L ‐LA as the starting material, the structure of the PLGA copolymer was relatively simple, and its properties were apt to be controlled by its GA chain segment. When the feed molar percentage of the monomer (LA or GA) was more than or equal to 90%, the copolymer was apt to be crystalline, and the aptness was more obvious for the L ‐LA monomer. The composition percentage of GA in PLGA was not only higher than the feed molar percentage of GA, but also, the GA percentage in D,L ‐PLGA was higher than in L ‐PLGA. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 244–252, 2006     

Enhanced foamability of isotactic polypropylene composites by polypropylene‐graft‐carbon nanotube

In this article, utilizing a nucleophilic substitution reaction between epoxy group in polypropylene‐graft‐glycidyl methacrylate (PP‐g‐GMA) and carboxyl groups in oxidized carbon nanotubes (O‐CNTs), PP‐g‐CNT was fabricated for reinforcing the interfacial adhesion between CNTs and polypropylene (PP) matrix, favoring the enhancement of melt strength and elastic modulus, i.e., enhancing the foaming ability of PP composites. Cellular structure and thermo‐mechanical properties of PP foams were characterized by scanning electron microscopy and dynamic mechanical analysis, respectively. The average cell diameter of PP foams decreased from 289.2 (PP‐g‐GMA) to 96.7 μm (PP‐g‐CNT foams with 2.0 wt % O‐CNT) and the distribution of cell size also became more uniform. The storage modulus of PP‐g‐CNT foams increased by nearly 62.5% at ?40°C, compared with that of PP‐g‐GMA foams. This work also provided a new procedure for improving the foam ability and thermo‐mechanical property of PP composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 961‐968, 2013     

Novel intercalated nanocomposites of polypropylene/organic‐rectorite/polyethylene‐octene elastomer: Rheology,crystallization kinetics,and thermal properties

The melt blending method was applied to prepare ternary composites of polypropylene (PP)/organic‐rectorite (OREC)/polyethylene‐octene elastomer (POE) at constant content of 2 phr (parts per hundred PP) of OREC and 5, 10, 15 phr of POE (named PRE25, PRE210, and PRE215, separately) via twin‐screw extruder. At the same time the binary composites of OREC/PP at 2 phr loading of OREC, named PR2 were prepared in order to investigate effects of OREC and POE on rheology and crystallization properties of composites. The rheology was characterized on capillary rheometer, nonisothermal crystallization kinetics on differential scanning calorimetry (DSC), and thermal stability properties on thermogravimetric analysis (TG). It is found that melting PR2 and PRE systems conform to the law of Non‐Newton and shear‐thinning behavior is observed for both systems. The apparent viscosity of the melt decreases with the increase of POE loadings. The crystallization halftime (t_1/2) of PRE is shorter, the rate constant Zc larger, which indicates OREC and POE has the heterogeneous nucleation effect and the crystallization rate of PP was increased. The enthalpy of PRE is lower than that of PR2 and pure PP at the same conditions, which shows that the relative crystallinity of PRE composites are reduced. TG curves show that the ternary systems have higher thermal stability in contrast with pure PP. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1915–1921, 2005     

Modification of polymers using multilayered “smart pellet” additives: Part II

A magnesium-based inorganic whisker was compounded with polypropylene and with polysulfone (FP/PP and FPSF/PP^*, respectively) and then multilayered into alternating structures with unfilled polypropylene (PP). These multilayered materials were cut into FP/PP and FPSF/PP^* “smart pellets”, which were then added to polypropylene matrix polymer as masterbatches to deliver potential reinforcement to injection molded parts. The morphologies of both the smart pellets and the composites produced with them were studied by scanning electron microscopy (SEM). The inorganic whiskers were found to be aligned in the machine direction in the smart pellets. Mechanical properties of the composites were investigated by performing tensile, flexural, and impact strength tests. Inorganic whiskers combined with PSF offered higher flexural modulus in comparison to those via conventional blending; no significant improvement was observed in tensile modulus or impact strength of these composites.     

Antimicrobial nanocomposites and electrospun coatings based on poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) and copper oxide nanoparticles for active packaging and coating applications

Active biodegradable poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) melt mixed nanocomposites and bilayer structures containing copper oxide (CuO) nanoparticles were developed and characterized. The bilayer structures consisted of a bottom layer of compression molded PHBV3 (3% mol valerate) coated with an active electrospun fibers mat made with CuO nanoparticles and PHBV18 (18% valerate) derived from microbial mixed cultures and cheese whey. The results showed that the water vapor permeability increased with the CuO addition while the oxygen barrier properties were slightly enhanced by the addition of 0.05 wt % CuO nanoparticles to nanocomposite films but a negligible effect was registered for the bilayer structures. However, the mechanical properties were modified by the addition of CuO nanoparticles. Interestingly, by incorporating highly dispersed and distributed CuO nanoparticles in a coating by electrospinning, a lower metal oxide loading was required to exhibit significant bactericidal and virucidal performance against the food‐borne pathogens Salmonella enterica, Listeria monocytogenes, and murine norovirus. The biodisintegration tests of the samples under composting conditions showed that even the 0.05% CuO‐coated structures biodegraded within 35 days. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45673.     

Polypropylene‐organoclay nanocomposite: Preparation,microstructure, and mechanical properties

A series of polypropylene (PP) nanocomposites containing 2, 4, and 6 wt % of an organophilic montmorillonite clay was prepared via direct melt mixing in the presence of maleic anhydride grafted polypropylene (PP‐g‐MAH) as compatibilizing agent. Microstructure characterization was performed by X‐ray diffraction analysis. Nanocomposites exhibited a 15 and 22% enhancement in tensile modulus and impact strength, respectively. The heat deflection temperature of PP nanocomposites was 36°C greater than for pure PP. Thermal and mechanical properties of nanocomposites were compared to properties of traditional PP‐talc and PP‐glass fiber composites. The results showed that the properties of nanocomposites improved compared to ordinary polypropylene composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Compatibilization and toughening of immiscible ternary blends of polyamide 6, polypropylene (or a propylene—Ethylene copolymer), and polystyrene

In this work, typical ternary blends of three versatile polymers—polyamide 6, a propylene–ethylene copolymer (co‐PP), and polystyrene—were studied. As a compatibilizer, co‐PP with randomly dispersed minor ethylene units was multimonomer‐melt‐grafted in the presence of maleic anhydride, styrene, and dicumyl peroxide. The influence of the ethylene content in co‐PP and the blend composition on the performance was investigated. Scanning electron microscopy images showed an obvious decrease in the droplet size of the dispersed phase with increases in the compatibilizer content and number of ethylene units in co‐PP. Peaks of tan δ/temperature curves approaching the glass‐transition temperatures of the components were observed with dynamic mechanical thermal analysis. The improved mechanical properties implied good compatibility of the components in the blends. Significant toughening was achieved when the concentration of co‐PP was increased from 15 to 25 wt %: the elongation at break of the compatibilized blends increased dozens of times in comparison with the elongation at break of the uncompatibilized blends. The introduction of the multimonomer‐melt‐grafted co‐PP was shown to be an effective approach for improving immiscible multipolymer blends and to have practical potential. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Properties of poly(butylene adipate‐co‐terephthalate) and sunflower head residue biocomposites

Utilization of low‐value agricultural waste for polymer composite materials has great environmental and economical benefits. Sunflower head residue (SHR) as an agricultural waste may be used as a reinforcement in polymeric materials because of its fiber characteristics. In this work, composites of biodegradable poly(butylene adipate‐co‐terephthalate) (PBAT) and SHR were prepared via melt‐extrusion compounding. To improve interfacial compatibility, maleic anhydride (MA) grafted PBAT (PBAT‐g‐MA) was prepared and used as a compatibilizer for the PBAT/SHR composites. The effects of the concentrations of SHR and PBAT‐g‐MA on the morphology, mechanical properties, melt rheology, and water resistance of the composites were examined. Interfacial adhesion between phases in the PBAT/SHR composites was enhanced by the introduction PBAT‐g‐MA as interface‐strengthening agent, resulting in improved mechanical properties and moisture resistance of the composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44644.     

Artificial weathering effect on the structure and properties of polypropylene/polyamide‐6 blends compatibilized with PP‐g‐MA

The degradation of uncompatibilized and compatibilized PP/PA‐6 (70/30 wt %) with PP‐g‐MA under accelerated UV light was investigated using Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy, melt flow index (MFI) tester, tensile test, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). FTIR analysis of the structure of the compatibilized and uncompatibilized blends after exposure to UV light showed the formation of photoproducts corresponding to both components. The MFI and mechanical results obtained revealed that photooxidation started primarily in PA‐6 rather than PP. In addition, the uncompatibilized blends exhibited a higher degradation rate compared to neat polymers for long exposure time, and the addition of PP‐g‐MA increased slightly their ageing rate in accordance with TGA data. Further, DSC analysis showed an increase in the crystallinity index and a decrease in the melting temperature of PP and PA‐6 after UV exposure either as neat polymers or as blend components. SEM micrographs of the cryo‐fractured surfaces of the samples illustrated the formation of cracks and fractures after UV irradiation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41722.     

Preparation and delayed release of poly(lactide‐ co‐glycolide)/ketoconazole composite fiber mats

In this study, slow release materials–poly(lactide‐co‐glycolide) (PLGA) ultrafine fiber mats containing different ketoconazole (KCZ) contents were prepared and their release behaviors were investigated in vitro. PLGA/KCZ ultrafine fiber mats were prepared via electrospinning and characterized by means of scanning electron microscope, Fourier transform infrared, X‐ray diffraction (XRD), and thermal gravimetric analysis. The slow release properties of PLGA/KCZ fiber mats in vitro were studied by measuring the concentrations of KCZ dissolved in the phosphate buffered solution (pH = 4.5) at a programmed time. Results indicated that KCZ could be dispersed in PLGA very well in a wide range of KCZ content from 10 to 100% with respect to PLGA. Most KCZ in PLGA fibers were physically dispersed. The thermal decomposition temperature of PLGA was lowered due to the incorporation of KCZ. With increased drug concentration, the release amount would increase in unit time. The two‐stage releases would be sustained to achieve the effective utilization of KCZ. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers