Centrifugally spun mats based on biopolyesters/hydroxyapatite and their potential as bone scaffolds

This work studied the potential of centrifugal spinning for the production of fibrous materials based on poly(D,L-lactic acid) (PDLLA) and poly(3-hydroxybutyrate) (PHB) with hydroxyapatite nanoparticles (n-Hap). The influence of n-Hap concentration (5, 10, and 15 wt.%) and spinneret angular speed on the final fiber morphology were analyzed. Further experimental evaluations were implemented to determine the effect of n-Hap on the thermal and mechanical performance. The optimum parameters that show a balance among high yield production of homogeneous fibers with the smallest fiber average diameter were found to be at 5 wt.% of n-Hap processed at 7000 rpm for PDLLA, and 5, 10, and 15 wt.% of n-Hap at 6000 rpm for PHB. The thermal stability, for both systems, was not significantly affected. The mechanical performance of PHB systems was improved with the addition of n-Hap. Osteoblast cell viability tests depicted a favorable cell response on the PDLLA systems.     

Elaboration of Ultra‐High Molecular Weight Polyethylene/Carbon Nanotubes Electrospun Composite Fibers

Micron‐sized fibers of UHMWPE reinforced with CNT were fabricated by the electrospinning process. Conditions for a metastable mutual solution of UHMWPE and CNTs were found at elevated temperature. These solutions were used for electrospining using a device having controlled temperature and gaseous environment around the electrospun liquid jet. The fabricated micron‐sized fibers exhibited the reinforcing CNTs as self‐organized nano‐ropes embedded within them. A post‐spinning drawing process enhanced the mechanical properties of the composite fibers to the level of 6.6 GPa strength and elongation at break of 6%. The CNT nano‐ropes form spontaneously in the liquid jet during electrospinning, and provide the reinforcement framework which is amenable for post‐drawing of the fibers for subsequent utilization as composite nanofibers. The experimental results exhibit the highest strength value reported to date for electrospun fibers.

     

Electrospun heat management polymeric materials of interest in food refrigeration and packaging

The use of latent heat storage materials using phase change materials (PCMs) is an effective way of buffering thermal fluctuations and has the advantages of high‐energy storage density and the isothermal nature of the storage process. The aim of this work was to develop slabs with energy storage capacity for their application in refrigerated foods. To this end, polycaprolactone (PCL) and polystyrene (PS) were used as encapsulating matrices of a PCM, specifically RT5 (a paraffin which has a transition temperature at 5°C), by using electrohydrodynamic processing. The effect of storage temperature (4°C and 25°C) and time on the morphology and thermal characteristics of the PCL/RT5 and PS/RT5 slabs was evaluated. Results showed that RT5 can be properly encapsulated inside both polymers, although PCL provided better encapsulation efficiency. Encapsulation efficiency was affected not only by the polymer matrix but also by storage time at 25°C. The greatest encapsulation efficiency (98.6%) and optimum heat management performance was achieved for PCL/PCM slabs stored at 4°C, corresponding to materials composed of ～44 wt % of PCM (core material) and ～56 wt % of the PCL shell material. These temperature buffering materials can be of great interest to preserve the quality of packaged foods and to increase efficiency and reduce energy consumption in refrigeration equipment. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40661.     

Recent Advances in Needleless Electrospinning of Ultrathin Fibers: From Academia to Industrial Production

Electrospinning (e‐spinning) has been extensively explored as a simple, versatile, and cost‐effective method in preparing ultrathin fibers from a wide variety of materials. Electrospun (e‐spun) ultrathin fibers are now widely used in tissue scaffold, wound dressing, energy harvesting and storage, environment engineering, catalyst, and textile. However, compared with conventional fiber industry, one major challenge associated with e‐spinning technology is its production rate. Over the last decade, compared with conventional needle e‐spinning, needleless e‐spinning has emerged as the most efficient strategy for large‐scale production of ultrathin fibers. For example, rolling cylinder and stationary wire as spinnerets have been commercialized successfully for significantly improving throughput of e‐spun fibers. The significant advancements in needleless e‐spinning approaches, including spinneret structures, productivity, and fiber quality are reviewed. In addition, some striking examples of innovative device designs toward higher throughput, as well as available industrial‐scale equipment and commercial applications in the market are highlighted.

     

Harnessing the Melting Peculiarities of Ultra‐High Molecular Weight Polyethylene Fibers for the Processing of Compacted Fiber Composites

Summary: Compacted fiber composites offer unique properties due to their lack of an extraneous matrix. The conditions of processing ultra‐high molecular weight polyethylene (UHMWPE) fibers were simulated in a heated pressure cell. In situ X‐ray diffraction measurements were used to follow the relevant transitions and the changes in the degree of crystallinity during melting and crystallization. The results strongly support the suggestion that the hexagonal crystal phase, in which the chain conformation is extremely mobile on the segmental level, constitutes the physical basis of compaction technologies for processing UHMWPE fibers into a single‐polymer composite. This report suggests that using a pseudo‐phase diagram outlining the occurrence of different phases during slow heating and the degree of crystallinity can provide valuable insight into the technological parameters relevant for optimal processing conditions.

Degree of crystallinity as a function of pressure and temperature in a region relevant to compaction processes.     

Unmodified and Modified Surface Sisal Fibers as Reinforcement of Phenolic and Lignophenolic Matrices Composites: Thermal Analyses of Fibers and Composites

Summary: The study and development of polymeric composite materials, especially using lignocellulosic fibers, have received increasing attention. This is interesting from the environmental and economical viewpoints as lignocellulosic fibers are obtained from renewable resources. This work aims to contribute to reduce the dependency on materials from nonrenewable sources, by utilizing natural fibers (sisal) as reinforcing agents and lignin (a polyphenolic macromolecule obtained from lignocellulosic materials) to partially substitute phenol in a phenol‐formaldehyde resin. Besides, it was intended to evaluate how modifications applied on sisal fibers influence their properties and those of the composites reinforced with them, mainly thermal properties. Sisal fibers were modified by either (i) mercerization (NaOH 10%), (ii) esterification (succinic anhydride), or (iii) ionized air treatment (discharge current of 5 mA). Composites were made by mould compression, of various sisal fibers in combination with either phenol‐formaldehyde or lignin‐phenol‐formaldehyde resins. Sisal fibers and composites were characterized by thermogravimetry (TG) and DSC to establish their thermal stability. Scanning electron microscopy (SEM) was used to investigate the morphology of unmodified and modified surface sisal fibers as well as the fractured composites surface. Dynamic mechanical thermoanalysis (DMTA) was used to examine the influence of temperature on the composite mechanical properties. The results obtained for sisal fiber‐reinforced phenolic and lignophenolic composites showed that the use of lignin as a partial substitute of phenol in phenolic resins in applications different from the traditional ones, as for instance in other than adhesives is feasible.

Micrograph of the impact fracture surface of phenolic composite reinforced with mercerized sisal fiber (500 X).     

超高分子量聚乙烯纤维制备技术进展

介绍了超高分子量聚乙烯(UHMWPE)纤维的物理、化学等性质,列举了国内外生产UHMWPE纤维的主要厂家,重点介绍了目前UHMWPE纤维的制备技术现状,包括干法凝胶纺丝、湿法凝胶纺丝以及其他纺丝方法等,分析了UHMWPE纤维现有制备过程中所面临的问题,并提出进一步发展方向。     

Molecular weight dependency of refractive index increment of polystyrene determined by uniform oligomers

Molecular weight dependency of a specific UV absorption coefficient of polystyrene in solution was determined by supercritical fluid chromatography applied to equimolar and equimass mixtures of uniform polystyrenes whose degree of polymerization was n = 1 to 40. From the ratio between the response from a UV detector and that from a refractometer, we determined the refractive index increment dn/dc as a function of molecular weight for polystyrene in tetrahydrofuran at the wavelength λ = 633 nm. We found that dn/dc is well expressed as a linear function of the reciprocal of molecular weight for uniform polystyrenes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1101–1106, 2004     

Fabrication of Aligned Poly(L‐lactide) Fibers by Electrospinning and Drawing

A new target collector was designed for taking up aligned nanofibers by electrospinning. The collector consists of a rotor around which several fins were attached for winding electrospun filaments continuously in large amounts. The alignment of the nanofibers wound on the collector was affected by the electrospinning conditions, such as the needle‐to‐collector distance and the applied voltage, but not by the rotation speed of the collector. At a voltage of 0.5 kV · cm^?1, about 60% of the fibers were found to be aligned within an angle of ± 5° relative to the rotational direction of the collector. The fiber alignment was improved to 90% by drawing the fiber bundle 2–3 times at 110 °C. The drawing was also effective for crystal orientation of the fibers as revealed by WAXD. The drawn fibers show improved mechanical properties.

     

Molecular Architecture and Enhanced Thermal Stability of Electrospun Poly(ε‐caprolactone)/Aminopropyl Isobutyl Polyhedral Oligomeric Silsesquioxane Hybrid Fibers

Polymer‐based electrospun fibers have been intensively studied as antimicrobial membranes, drug carriers, and energetic materials. Inorganic fillers or small molecules have been routinely added into polymer matrices in order to enhance product functions. However, the electrospinning process is kinetically controlled and solvent rapidly evaporates due to the large surface‐to‐volume ratio of spinning liquid jet. When electrospinning a multicomponent system, complex phase behavior may occur and give rise to interesting internal structures of resulting products. Such kinetically driven phenomena deserve more attention for optimizing product performance. Here, electrospun poly(ε‐caprolactone)(PCL)/aminopropyl‐heptaisobutyl‐polyhedral oligomeric silsesquioxane (AMPOSS) fibers with AMPOSS content up to 30 wt% are studied as a model system to understand the impact of kinetically controlled phase separation on the fibers' internal structure, properties, and thermal stability. With sufficient AMPOSS loading, the hybrid fibers are found to have an AMPOSS‐shell/PCL‐core structure. The thermal stability of the as‐spun PCL/AMPOSS fibers is therefore greatly enhanced.

     

Recent Applications of X-ray Scattering Methods to Fibers and Plastics

Abstract

X-ray methods are potent and versatile tools for the structural characterization of matter. For our studies on semicrystalline plastics and on parts produced therefrom, we have developed special X-ray scattering techniques which are capable to deliver a wealth of structural information without the necessity to use very expensive equipment or laborious preparations of specimens. Some of the techniques utilizing linear position-sensitive detectors have been applied in the structural characterization of fibers as well. The wideangle techniques are described and their applications to selected examples, cellulose fibers and cross-sections of moldings from graphite-filled polypropylene, are illustrated.     

异戊二烯在聚苯乙烯高分子膜中的扩散系数测定

为了探讨在反应挤出过程中异戊二烯在聚苯乙烯中的扩散传递机理,采用石英弹簧法测定了298.15K、308.15K和318.15K下异戊二烯在聚苯乙烯膜中的吸收动力学曲线。探讨了温度、压力、分子量对扩散吸收的影响,并对实验结果进行了关联。结果表明异戊二烯在聚苯乙烯膜中的扩散吸收呈S型吸收,由吸收曲线获得了平均扩散系数和平衡溶解度。     

Development of polystyrene composites based on blue agave bagasse by in situ RAFT polymerization

A new approach for the production of polystyrene-blue agave bagasse (BAB) composite materials is presented. In this approach, dried powdered raw BAB is press molded in the presence of a coupling agent based on glycidyl methacrylate (GMA), producing a hybrid material of poly(GMA) grafted onto BAB. The in situ reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene in presence of this poly(GMA)-graft-BAB hybrid material results in a reinforced composite material. These composites are characterized by Fourier-transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, gel permeation chromatography, scanning electron microscopy, impact test analyses, and dynamic mechanical analysis. The characterization results show that the amount of GMA coupling agent plays a key role in the efficiency of the process, manifested as improvement of the mechanical properties of polystyrene. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47089.     

α位羰基烯胺酮代间苯二酚的合成和荧光性质研究

合成了一类α位羰基烯胺酮间苯二酚新化合物,通过1H NMR,13C NMR,IR,EA等方法进行了表征,并对8种化合物与五种不同的金属阳离子作用后的荧光光谱和紫外-可见吸收光谱的变化进行了对比研究,发现1-(5-乙酰基-2,4-二羟苯基-3-(4-氯苯胺)丙-2-烯酮化合物)对过渡金属铜离子有明显的特征荧光淬灭识别能力,因此可以作为一种金属离子荧光分子探针选择性识别过渡金属Cu2+离子。     

Electrospun fibers of poly(l‐lactic acid) containing lovastatin with potential applications in drug delivery

Lovastatin (Merck's Mevacor) is a statin drug designed to lower cholesterol, and reduce the risk of heart attack and stroke. We use electrospinning to combine the biomedical properties of lovastatin with the advantages of electrospun fibers to prepare a composite biomaterial for lovastatin delivery. Poly(l ‐lactic acid) (PLLA), a biodegradable and biocompatible polymer, was co‐spun with lovastatin. Incorporation of lovastatin at 5 or 10 wt % improved fiber alignment and surface smoothness, and increased fiber diameter. Influence of lovastatin on the phase structure (crystal, mobile amorphous, and rigid amorphous fractions) was investigated using scanning calorimetry and synchrotron X‐ray scattering. Addition of lovastatin resulted in increased crystallinity and reduced mobile amorphous fraction. PLLA fibers were characterized in terms of their drug release kinetics in comparison to PLLA film. High drug entrapment efficiency (ranging from 72% to 82%) and appropriate release profiles were achieved. In vitro drug release studies demonstrated that release occurred in two stages: an initial rapid release over the first day and a slower second stage of release which approached a plateau after 7 days. PLLA fibers have a higher release rate than comparable film. Electrospun biomaterial fibers of PLLA provide a promising new release strategy for delivery of lovastatin. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45287.     

Infrared Spectroscopic Investigation of Hydrogen Bonding in EVOH Containing PVA Fibers

Fibers of poly(vinyl alcohol) (PVA) containing ethylene‐vinyl alcohol copolymer (EVOH) are made by gel spinning. By using IR spectroscopy, the hydrogen bonds of the PVA/EVOH fibers with different EVOH content and different draw ratio are discussed. The peaks in the neighborhood of 3 400 cm^–1 and the peaks near 3 600 cm^–1 are used to analyze the hydroxyl absorption engaged in hydrogen bonds and the free hydroxyl absorption, respectively. As for PVA/EVOH films, with increasing EVOH content the H‐bond is gradually weakened. As for fibers, however, with increasing EVOH content the strength of the H‐bond increases, while the number of H‐bonds is decreased. Similarly, with increasing draw ratio of the PVA/EVOH fibers, the strength of H‐bond increases, while the number of H‐bonds seems decreased. Higher EVOH content in the PVA/EVOH fibers causes a higher maximum draw ratio because of weakening of the H‐bond. However, higher draw ratio does not always cause better mechanical properties of PVA/EVOH fibers.     

Effect of winding speed on the structure and properties of as‐spun poly(trimethylene 2,6‐naphthalenedicarboxylate) fibers as compared to poly(ethylene terephthalate) fibers

We present a comparative study of melt spinning of poly(trimethylene 2,6‐naphthalenedicarboxylate) (PTN) and poly(ethylene terephthalate) (PET) fibers with respect to the effect of winding speed (2000–6000 m/min): Structural changes were followed by X‐ray analysis, calorimetry, and measurements of density, boiling water shrinkage, and birefringence. As‐spun PTN fibers exhibited a low degree of crystallinity at relatively low speeds (< 2000 m/min). An increase in winding speed up to 6000 m/min only resulted in a minor enhancement of crystallinity and orientation. The small change of structural parameters accounted for the fact that tenacity and modulus did not rise significantly with increasing winding speed, contrary to the PET fibers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2489–2497, 2002     

Dwarf Cavendish as a Source of Natural Fibers in Poly(propylene)‐Based Composites

Summary: Composite materials were prepared by compounding and hot‐pressing PP or MAPP and lignocellulosic fibers extracted from the rachis of Musa acuminate Colla var. Dwarf Cavendish banana tree. The fibers were used as raw filler or after a chemical treatment expected to remove most of the extractible compounds. The resulting materials were characterized using SEM, DSC, DMA, tensile tests and water sorption experiments. All results show that the main aspect involved in the interfacial adhesion between the polar filler and the non‐polar matrix is the extraction of lignin and fatty substances. This results in higher values of the degree of crystallinity and crystallization temperature of the matrix, higher mechanical properties and lower water sensitivity.

Scanning electron micrograph showing the cross section of the lignocellulosic filler obtained from rachis of banana tree: (a) raw, and (b) extracted fibers.     

Method Development to Evaluate Melting Behavior of Glass Fiber-Reinforced Syndiotactic Polystyrene Composites in the Presence of Pressure Loading

Criteria of cycle time include metering, closing a mold, packing, holding, cooling, opening a mold and ejecting. Interestingly, metering time was found relatively lengthy in the composite of glass fiber (GF)-reinforced syndiotactic polystyrene (sPS) during injection molding. It was motivated by the ideas that analyzing dynamic thermal property may provide the correlation with metering time because differential scanning calorimeter does not fully provide dynamic thermal property. We created new measuring system to examine thermal behavior in the presence of pressure loading. The method was very effective to determine the melting rate of thermoplastics in the presence of pressure loadings.     

Molecular orientation in the surface layer of polytetrafluorinethylene

Attenuated total reflectance spectroscopy was used to study the orientation and deformation of molecular chains in polymers. Reflection and transmission spectra of the polytetrafluorinethylene (PTFE) films were obtained. Parameters of the macromolecule's degree of order were determined for the whole volume and for the surface layer of uniaxially orientated PTFE, and on this basis, we determined the character of dependence l^SL(L), where l^SL is the effective thickness of the surface layer and L is the film stretching degree. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1596–1599, 2002