Factors influencing the small‐scale melt spinning of poly(ε‐caprolactone) monofilament fibres

Some of the main factors affecting the small‐scale melt spinning of poly(ε‐caprolactone), PCL, monofilament fibres have been studied. These factors included spinning temperature, extrusion rate, take‐up rate and draw ratio. The underlying influence of the polymer's own characteristic properties, in particular its chemical structure, transition temperatures (T_g, T_m) and crystallizability, were also interpreted within the context of the melt spinning process. Physically, the as‐spun fibres obtained were uniform in diameter and smooth in surface appearance. They were also semi‐crystalline (>50%) in morphology. Mechanically, however, they were still very weak and highly extensible. Subsequent off‐line cold‐drawing at room temperature introduced the required degree of molecular orientation to reinforce the fibres, yielding tensile strengths of approaching 300 MPa. PCL fibres of precisely controlled physical dimensions and matrix morphology are attracting increasing interest for use in biomedical applications. This paper describes how this control can be achieved through the processing operation. Copyright © 2003 Society of Chemical Industry     

Titania-doped multi-walled carbon nanotubes epoxy composites: Enhanced dispersion and synergistic effects in multiphase nanocomposites

Multi-walled carbon nanotube-epoxy composites are modified with titania nanoparticles in order to obtain multiphase nanocomposites with an enhanced dispersion of carbon nanotubes. The dispersion is monitored using rheological and electrical conductivity measurements. An increase in dispersion quality can be correlated to an increased storage shear modulus of the uncured suspensions and to a decreased electrical conductivity in the bulk nanocomposite. The newly formed microstructure is revealed using transmission electron and optical microscopies. Due to chemical interactions between both types of nanoparticles an attractive potential is generated leading to a significant rearrangement in the particle network structure. Besides an enhanced dispersion, the hybrid structure leads to synergistic effects in terms of the glass transition of the nanocomposites. Although a decrease of the glass transition temperature (T_g) is observed for the nanocomposites containing only one type of filler, the combination of titania and carbon nanotubes into a hybrid structure reduces the decrease of T_g, thus demonstrating the potential of such hybrid structures as fillers for multi-functional epoxy nanocomposites.     

Synthesis and characterization of a random terpolymer of L‐lactide, ϵ‐caprolactone and glycolide

A random terpolymer of L ‐lactide (LL), ?‐caprolactone (CL) and glycolide (G) has been synthesized in bulk at 130 °C using stannous octoate as the coordination–insertion initiator. The terpolymer, poly(LL‐ran‐CL‐ran‐G), has been characterized by a combination of analytical techniques: GPC, ¹H NMR, ¹³C NMR, DSC and TG. Molecular weight characterization by GPC shows a unimodal molecular weight distribution with values of M _n = 1.01 × 10⁵ g mol^?1 and M _w / M _n = 2.17. Compositional and microstructural analysis by ¹H NMR and ¹³C NMR, respectively, reveal a terpolymer composition of LL:CL:G = 74:15:11 (mol%) with a chain microstructure consistent with random monomer sequencing. This latter view is supported by the terpolymer temperature transitions (T_g and T_m) from DSC and the thermal decomposition profile from TG. The results and, in particular, the conclusion that it is a random rather than a statistical terpolymer are discussed in the light of current theories regarding the mechanism of this type of polymerization. © 2001 Society of Chemical Industry     

Reduction of the polycyclic aromatic hydrocarbon (PAH) content of charcoal smoke during grilling by charcoal preparation using high carbonisation and a preheating step

Charcoal-grilling may lead to contamination of food with carcinogenic polycyclic aromatic hydrocarbons (PAHs) during the grilling process. The objective of this work was to determine the effect of charcoal preparation on 16 USEPA priority PAHs in the smoke produced during the grilling process. Firstly, mangrove charcoal was prepared at carbonisation temperatures of 500, 750 and 1000°C. The charcoal were then preheated by burning at 650°C. This preheating step is usually used to prepare hot charcoal for the grilling process in the food industry. In this study, charcoal was preheated at different burning times at 5, 20 min and 5 h, at which time partial and whole charcoal glowed, and charcoal was completely burnt, respectively. Finally, PAHs in the smoke were collected and determined by GC/MS. The result showed that charcoal prepared at a carbonisation temperature of 500°C had higher levels of PAHs released into the smoke. In contrast, charcoal produced at 750 and 1000°C had lower PAHs released for all burning times. In addition, PAHs released for 5, 20 min and 5 h of burning time were about 19.9, 1.2 and 0.7 µg g^?1 dry charcoal for charcoal produced at 500°C, and about 0.9–1.4, 0.8–1.2 and 0.15–0.3 µg g^?1 dry charcoal for charcoal produced at 750 and 1000°C, respectively. Therefore, this research suggests that food grilled using charcoal carbonised at a high temperature of about 750°C presents a lower risk of PAH contamination. In addition, in the preheating step, whole charcoal should fully glow in order to reduce the PAH content in charcoal before grilling.     

Synthesis,characterization and melt spinning of a block copolymer of L-lactide and ε -caprolactone for potential use as an absorbable monofilament surgical suture

This paper describes the synthesis and characterization of a block copolymer of L-lactide (LL) and ε -caprolactone (CL) and its subsequent melt spinning into a monofilament fiber. The synthesis reaction was a two-step process. In the first step, an approximately 50:50 mol% random copolymer, P(LL-co-CL), was synthesized via bulk copolymerization of LL and CL. This first-step prepolymer then became the macroinitiator in the second-step reaction in which more LL monomer was added to form a block copolymer, PLL-b-P(LL-co-CL)-b-PLL. Both the prepolymer and block copolymer were characterized by a combination of analytical techniques comprising dilute-solution viscometry, GPC, ¹H and ¹³C NMR, DSC and TG. The block copolymer was then processed into a monofilament fiber using a small-scale melt spinning apparatus. The fiber was spun with a minimum amount of chain orientation and crystallinity so that its semi-crystalline morphology could be constructed under more controlled conditions in subsequent off-line hot-drawing and annealing steps. In this way, the fiber’s tensile properties and dimensional stability were developed, as indicated by the changes in its stress-strain curve. The final drawn and annealed fiber had a tensile strength (> 400 MPa) approaching that of a commercial PDS II suture of similar size. It is considered that this type of block copolymer has the potential to be developed further as a lower-cost alternative to the current commercial monofilament surgical sutures.     

Degradation kinetics of monacolin K in red yeast rice powder using multiresponse modeling approach

The effects of storage temperature (4, 20, 30, 40, 50 °C) and atmospheric conditions in packages (vacuum, atmospheric) on degradation kinetics of monacolin K, an antihypercholesterolemic agent, in red yeast rice powder were investigated using multiresponse modeling approach. Storage of red yeast rice powder at 4 °C under vacuum package was found to enhance retention of monacolin K. Multiresponse modeling revealed degradation path of monacolin K acid form into their dehydromonacolin K and unknown product under vacuum package, while oxidized product was also formed under atmospheric package. Monacolin K lactone form and precursor were degraded into dehydromonacolin K lactone form, while degradation of dehydromonacolin K lactone form to unknown was more pronounced at temperature higher than 30 °C. Oxidized product was also generated from monacolin K lactone form in atmospheric package. High activation energy of monacolin K degradation in acid form indicated that degradation of monacolin K to their dehydromonacolin K was more susceptible to temperature change as compared to lactone form.