Richard Kotek

Effect of blend ratio on bulk properties and matrix-fibril morphology of polypropylene/nylon 6 polyblend fibers

Ternary blends of polypropylene (PP), nylon 6 (N6) and polypropylene grafted with maleic anhydride (PP/N6/PP-g-MAH) as compatibilizer with up to 50 wt% of N6 were investigated. PP-g-MAH content was varied from 2.5 to 10%. Blends of the two polymers PP/N6 (80/20) without the compatibilizer were also prepared using an internal batch mixer and studied. The ternary blends showed different rheological properties at low and high shear rates. The difference depended on the amount of N6 dispersed phase. Co-continuous morphology was observed for the blend containing 50% N6. This blend also exhibited higher viscosity at low shear rate and lower viscosity at high shear rates than the value calculated by the simple rule of mixture. At higher shear rates, viscosity was lower than that given by the rule of mixture for all blend ratios. An increase in viscosity was observed in the 80/20 PP/N6 blend after the concentration of the interfacial agent (PP-g-MAH) was increased. Polyblends containing up to 30% N6 could be successfully melt spun into fibers. DSC results showed that dispersed and matrix phases in the fiber maintained crystallinity comparable to or better than the corresponding values found in the neat fibers. The dispersed phase was found to contain fibrils. By using SEM and LSCM analyses we were able to show that the N6 droplets coalesced during melt spinning which led to the development of fibrillar morphology.

Recent Advances in Polymer Fibers

In recent years, there has been steady progress in developing new polymers and functional polymer fibers. The objectives of this issue are to provide readers an overview of significant advances for the production of high performance fibers such as Kevlar, PBO, Spectra and Dyneema fibers and to describe new super strong M5 fibers, highly elastic XLA™ fibers and self‐crimping T‐400, T‐800, and other fibers. Additional goals are to present futuristic technologies such as shape memory fibers and compare them with innovative spandex fibers as well as to describe unique nanofibers from biopolymers by using novel electrospinning methods. Finally new, high performance poly(ethylene naphthalate) fibers will be reviewed.

Enzymatic hydrolysis of PTT polymers and oligomers

Oligomers and polymers (film, fabrics) of the linear aromatic polyester poly(trimethylene terephthalate) (PTT) were treated with polyesterases from Thermomyces lanuginosus, Penicillium citrinum, Thermobifida fusca and Fusarium solani pisi. The cutinase from T. fusca was found to release the highest amounts of hydrolysis products from PTT materials and was able to open and hydrolyse a cyclic PTT dimer according to RP-HPLC-UV detection. In contrast, the lipase from T. lanuginosus also showed activity on the PTT fibres and on bis(3-hydroxypropyl) terephthalate (BHPT) but was not able to hydrolyse the polymer film, mono(3-hydroxypropyl) terephthalate (MHPT) nor the cyclic dimer of PTT. As control enzymes inhibited with mercury chloride were used. Surface hydrophilicity changes were investigated with contact angle measurements and the degree of crystallinity changes were determined with DSC.

Thermotropic homopolyesters—VI. A study of polymers based on 4′-hydroxyphenyl-4-hydroxybenzoate

Abstract Polyesters were synthesized from 4′-acetoxyphenyl-4-acetoxybenzoate and dibasic acids having 6–12 methylene units using the transesterification procedure described by van Luyen and Strzelecki. These polymers are designated Sn, where n is the number of methylene units in the diacid. The transition temperatures of our polymers stand in reasonable agreement with those reported by Strzelecki and Liebert. The nematic phase extends over a broad temperature range (70–100°), and the biphasic region spans an additional 50°. The texture of the nematic phase is normal for S7-1 having ηinh = 0.30 dl/g, but the other polymers show bright nematic droplets on a darker background. The density of droplets decreases with increasing ηinh in the S7 series, and as η is increased for the other polymer homologues. Only S7-1 exhibits Williams domains on application of an electric field. Quite different properties are found for the polyester having ηinh = 0.80 dl/g prepared from 4′-hydroxyphenyl-4-hydroxybenzoate and the diacid chloride. It melted sharply 24° higher, and its nematic phase showed a normal texture. Moreover, its nematic-isotropic transition appears in the DSC as a sharp peak, and the biphasic region spans only 9°. We believe the transesterification reaction occasionally involves the internal ester linkage in the monomer unit, producing a polymer with no definite repeating unit structure and a distribution of hard segment lengths.

The promotion of axon extension in vitro using polymer-templated fibrin scaffolds.

Biomaterial nerve cuffs are a clinical alternative to autografts and allografts as a means to repair segmental peripheral nerve defects. However, existing clinical biomaterial constructs lack true incorporation of physical guidance cues into their design. In both two- and three-dimensional systems, it is known that substrate geometry directly affects rates of axon migration. However, the ability to incorporate these cues into biomaterial scaffolds of sufficient porosity to promote robust nerve regeneration in three-dimensional systems is a challenge. We have developed fibrin constructs fabricated by a sacrificial templating approach, yielding scaffolds with multiple 10-250 μm diameter conduits depending on the diameter of the template fibers. The resulting scaffolds contained numerous, highly aligned conduits, had porosity of ∼ 80%, and showed mechanical properties comparable to native nerve (150-300 kPa Youngs modulus). We studied the effects of the conduit diameters on the rate of axon migration through the scaffold to investigate if manipulation of this geometry could be used to ultimately promote more rapid bridging of the scaffold. All diameters studied led to axon migration, but in contrast to effects of fiber diameters in other systems, the rate of axon migration was independent of conduit diameter in these templated scaffolds. However, aligned conduits did support more rapid axon migration than non-aligned, tortuous controls.

Novel Methods for Obtaining High Modulus Aliphatic Polyamide Fibers

Super high modulus polyethylene fibers can be created by converting high molecular weight flexible PE chains into highly oriented and extended chain conformations. However, unlike polyethylene, aliphatic polyamides have very high cohesive energy and therefore cannot be easily drawn and highly oriented. This review addresses this fundamental problem by analyzing various novel approaches that can be used to suppress hydrogen bonding in these types of polyamides. Plasticization of such polymers with ammonia, iodine, salts, and Lewis acids, as well as dry spinning, wet spinning, and gel spinning, are discussed. Specialized techniques that involve vibrational zone drawing and annealing as well as laser heating zone drawing and annealing are also reviewed. Some of these methods definitely lead to remarkable improvements in initial modulus and other mechanical properties. The development of recombinant spider silk proteins as well progress in spinning these materials is also reported. The advantages and disadvantages of all of these processes are then summarized.

Properties of Antibacterial Polypropylene/Nanometal Composite Fibers

Melt spinning of polypropylene fibers containing silver and zinc nanoparticles was investigated. The nanometals were generally uniformly dispersed in polypropylene, but aggregation of these materials was observed on fiber surface and in fiber cross-sections. The mechanical properties of the resulted composite fibers with low concentration of nanometal were comparable to those for the control PP yarns. Extruded composite fibers that contained 0.72% silver and 0.60% zinc nanoparticles had outstanding antibacterial efficacy as documented by the percentage count reduction growth of Escherichia coli and Staphylococcus aureus. Fibers containing silver particles had improved antistatic properties.

Advances in the Production of Poly(ethylene naphthalate) Fibers

Recently with the availability of monomers for poly(ethylene naphthalate) (PEN) at a large scale and low cost, much attention has been paid to develop PEN fibers, based on their superior mechanical and thermal properties, to compete with the most commercially important poly(ethylene terephthalate) fibers, especially in some performance‐driven markets. In this review, technical papers, product reports, and patents are reviewed to summarize the developments in the production of PEN fibers via melt‐spinning. Mechanical properties of PEN fibers are presented as a function of spinning and drawing parameters. Morphology of PEN fibers are also discussed to understand factors controlling the fiber properties.

Studies on poly(trimethylene terephthalate) filaments containing silver.

Two methods were used to incorporate silver ions into poly(trimethylene terephthalate) (PTT) fibers. The first technique involved the direct addition of silver (I) sulfadiazine into PTT polymer prior to extrusion. The second method involved the use of silver-exchanged zeolites. Although no optimization with silver-exchanged zeolites was conducted, this study clearly showed that PTT fibers containing sufficient amounts of silver ions are effective in reducing pathological microorganisms such as Escherichia coli. Incorporation of silver-exchanged zeolites into PTT imparted a silver color to the fibers which may be attributed to the partial reduction of silver ions during spinning at 256°C. Because of the decomposition of silver (I) sulfadiazine, the spinnability of PTT fiber sample was not satisfactory and, therefore, this compound cannot be used as a carrier of silver ions in PTT. The thermal, tensile and antimicrobial properties of the spun filaments are reported in this paper.

Preparation of antibacterial PVA and PEO nanofibers containing Lawsonia Inermis (henna) leaf extracts

Concerns about health issues and environmental pollution stimulate research to find new health and hygiene related products with healing properties and minimum negative effect on the environment. Development of new, natural antibacterial agents has become one of the most important research areas to combat some pathogens such as Gram- positive and Gram-negative bacteria, fungi, algae, yeast, and some microorganisms which cause serious human infections. Lawsonia Inermis (henna) leaf extracts for preparation of antibacterial poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA) nanofibers via electrospinning technique were investigated. PEO and PVA based electrospun fibers containing henna extract were verified by the appearance of FTIR peaks corresponding to the pure extract. Our study demonstrates that 2.793 wt.% Li in PVA and PEO based solutions showed bactericidal effects against Staphylococcus aureus and bacteriostatic action to Escherichia coli. Concentrations of henna leaf extract strongly impacted antibacterial activities against both bacteria. Henna leaves have a great potential to be used as a source of a potent eco-friendly antimicrobial agent.