Colin Birkinshaw

Heavy metal adsorbents prepared from the modification of cellulose: A review

A number of industries currently produce varying concentrations of heavy metal laden waste streams with significant consequences for any receiving environmental compartment. In recent years, increasing emphasis has been placed on environmental impact minimisation and resulting from this the range and capability of natural and prepared materials capable of heavy metal removal has seen steady development. In particular considerable work has been carried out on the use of both natural materials and their modifications. These natural materials, in many instances are relatively cheap, abundant in supply and have significant potential for modification and ultimately enhancement of their adsorption capabilities. This review paper reviews the current state of research on the use of the naturally occurring material cellulose, its modified forms and their efficacy as adsorbents for the removal of heavy metals from waste streams. Adsorbents based on direct modification of cellulose are evaluated initially and subsequently modifications resulting from the grafting of selected monomers to the cellulose backbone with subsequent functionalisation are assessed. The heavy metal adsorption capacities for these modified cellulose materials were found to be significant and levels of uptake were comparable, in many instances, to both other naturally occurring adsorbent materials and commercial ion exchange type resins. Many of the modified cellulose adsorbents proved regenerable and re-usable over a number of adsorption/desorption cycles allowing recovery of the adsorbed heavy metal in a more concentrated form.

Hyaluronic acid based scaffolds for tissue engineering--a review.

This review focuses on hyaluronic acid (HA) tissue scaffolding materials. Scaffolds are defined in terms of formation mechanisms and mode of action. Solution properties are discussed as an understanding of the hydrodynamics of HA is fundamental in optimising the subsequent modification and the chemistries behind important tissue engineering applications that are emerging from recent research on this increasingly valuable carbohydrate polymer are described. Key scaffold characteristics such as mechanical, biological function and degradation are discussed. The latest technologies behind scaffold processing are assessed and the applications of HA based scaffolds are discussed.

Poly n-butyl cyanoacrylate nanoparticles: a mechanistic study of polymerisation and particle formation

Poly n-butyl cyanoacrylate has been used in the synthesis of nanoparticles by dispersion polymerisation in aqueous media. Following establishment of a thermometric procedure for assessment of monomer reactivity, the relationships between monomer-polymer conversion reactions and particle development at various pH values was investigated. Particle size was measured during the synthesis process using a laser diffraction technique and final particle character was assessed by scanning electron microscopy. Optimum conditions for particle production were a dispersion medium of pH 2.5 at a temperature of 65 degrees C, with dextran 70 used as a steric stabiliser. In the presence of dextran, following a period of equilibration, colloidally stable particles form, but in the absence of dextran particles are colloidally unstable and rapidly coalesce. Measurement of molecular weight changes through the synthesis process show an upward shift consistent with the initial formation of oligomers, which then further polymerise through a re-initiation re-polymerisation process until an equilibrium molecular weight is reached.

Physical properties of crosslinked hyaluronic acid hydrogels

In order to improve the mechanical properties and control the degradation rate of hyaluronic acid (HA) an investigation of the structural and mechanical properties of the hydrogels crosslinked using divinyl sulfone (DVS), glutaraldehyde (GTA) and freeze-thawing, or autocrosslinking has been carried out. The thermal and mechanical properties of the gels were characterised by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and compression tests. The solution degradation products of each system have been analysed using size exclusion chromatography (SEC) and the Zimm–Stockmayer theory applied. Autocrosslinked gels swell the most quickly, whereas the GTA crosslinked gels swell most slowly. The stability of the autocrosslinked gels improves with a reduction in solution pH, but is still poor. GTA and DVS crosslinked gels are robust and elastic when water swollen, with glass transition values around 20°C. SEC results show that the water soluble degradation products of the gels show a reduction in the radius of gyration at any particular molecular weight and this is interpreted as indicating increased hydrophobicity arising from chemical modification.

Irradiation of poly-d,l-lactide

Compression-moulded samples of poly-d,l-lactide have been γ-irradiated in air to give received doses up to 10 Mrad. Molecular weight and mechanical property changes have been established and are consistent with a random scission process. Substantial embrittlement occurs at the higher dose levels. The radiochemical yield for scission G(s) has been calculated to be 2·9 over the dose range examined. The properties of irradiated materials have been monitored over a 504-day period and show no evidence of post-irradiation aging. Moisture uptake has been measured by immersion in pH 7·4 buffer at 37°C and indicates that the irradiated material absorbs water at a slightly slower rate than the unirradiated material. The primary effect of irradiation on hydrolytic degradation is associated with the initial reduction of molecular weight and there are no subsequent changes in degradation mechanism.

The thermal stability and thermal degradation of blends of syndiotactic polystyrene and polyphenylene ether

Blends of syndiotactic polystyrene (sPS) and polyphenylene ether (PPE) have been prepared by co-precipitation from solution, followed by compression moulding. Three different molecular weight polystyrenes were used. Differential scanning calorimetry shows that partial crystallization of the sPS occurs, but a single glass transition indicates that the blend components are miscible in the amorphous phase. Thermogravimetry has been used to compare the thermal stability of the blends and the pure polymers, and IR spectroscopy used to give information on the structural changes consequent upon heating. The three different molecular weight polystyrenes degraded in an identical manner, suggesting that initiation is by random chain scission. The onset of sPS degradation in the blend occurs at higher temperatures than in the pure polymer indicating stabilisaton of that component, whilst degradation of PPE in the blends is accelerated relative to the pure polymer. IR spectroscopy shows that PPE undergoes structural rearrangement in which the ether link is broken and chain continuity is re-established through the methyl group before any mass loss is apparent. The sPS degradation temperatures are coincident with the temperature of this rearrangement and it is proposed that the PPE acts as a radical acceptor, interrupting the intermolecular transfer process in the degrading polystyrene. This cross-termination process limits the PPE rearrangement and consequently reduces the ultimate stability of that polymer.

The thermal stability of some vinylidene chloride copolymers

Abstract Vinylidene chloride (VdC) was copolymerised with a series of acrylates and methacrylate monomers to investigate the effect of increasing side chain length on thermal stability and oxygen barrier behaviour. Suspension polymerisation was used, and the comonomer contents were 7.5 and 12.5 mol%. The homo-polymer was also synthesised and investigated. Rates of dehydrochlorination were measured at 180, 195 and 210°C and the activation energies calculated. The volatile degradation products were examined using chromatography and the degradation residue by IR spectroscopy. Percentage crystallinity was measured by X-ray diffraction and oxygen permeation was measured using the Mocon method. The results showed that the VdC–methacrylate copolymers had much higher rates of dehydrochlorination and lower activation energies than the VdC–acrylate copolymers. The behaviour of the homopolymer was intermediate. This relative instability of the methacrylate copolymers is though to be due to them having greater block character, and therefore a higher potential for unzipping reactions, and also to the possibility of a neighbouring group activation process. The crystallinities of the copolymers was less than that of the homopolymer but crystallinity was not shown to be a major factor in determining barrier properties. The VdC copolymers with the best balance between their thermal stability and barrier behaviour were those with methyl acrylate, which are presently used commercially. Increasing the acrylate comonomer side chain length confers no stability advantage.

Preparation of Poly(butyl cyanoacrylate) Nanoparticles by Aqueous Dispersion Polymerisation in the Presence of Insulin

Butyl cyanoacrylate has been polymerised by dispersion in acidified water, with introduction of insulin during the reaction, to yield nanoparticles containing the drug. Polymer molecular weight measurement, carried out by gel permeation chromatography, shows that insulin is capable of initiating polymerisation of this monomer, but if the drug is included at the beginning of the synthesis the reaction is not controllable and nanoparticles are not formed. Introduction of insulin into a dispersed monomer system that has already been initiated by the hydroxyl ion, but is still polymerising, gives a controllable synthesis yielding nanoparticles. Molecular weight measurement suggests that the insulin is covalently bound to the polymer chain.

The distribution of oxidation products in irradiated ultra-high molecular weight polyethylene

Abstract Ultra high molecular weight polyethylene (UHMWPE) has been irradiated in air and nitrogen to various received doses and stored in air for periods of time up to 84 months. The degree of oxidation has been measured using a microscope-FTIR technique, which allows assessment of the distribution of oxidation products throughout the thickness of the specimen. Maximum oxidation occurs close to the surface and is dose-dependent; however, the depth of penetration of the oxidised zone depends on the ageing period. Materials stored in vacuo for 35 days prior to irradiation under nitrogen show reduced levels of oxidation but react further with time, implying that the irradiated material still contains reactive species. Newly exposed surfaces of materials irradiated in air to a received dose of 50 Mrad and stored in air for 84 months also show evidence of renewed oxidation, but ‘annealing’ at 90°C for 24 h reduces the reactivity. Taken in conjunction with other observations, the results suggest that the dominant process during ageing of irradiated UHMWPE is oxidative chain scission. It seems probable that the active species are either radicals generated during the initial irradiation or secondary radical rearrangement products.

Removal of Lead(II) Ions from Aqueous Solutions Using a Modified Cellulose Adsorbent

A series of adsorption studies were carried out on a glycidyl methacrylate-modified cellulose material functionalised with imidazole (cellulose–g-GMA-imidazole) to assess its capacity towards the removal of Pb(II) ions from aqueous solution. The study sought to establish the effect of a number of parameters on the removal of Pb(II) ions from solution by the cellulose–g-GMA-imidazole. The effect of initial metal concentration, contact time and solution temperature on the removal of Pb(II) ions from solution by the cellulose–g-GMA-imidazole was assessed. Cellulose–g-GMA-imidazole sorbent showed an uptake of ca. 72 mg/g of Pb(II) ions from aqueous solution at 23°C. The adsorption process is best described by the Langmuir adsorption model and the thermodynamics of the process suggest that the binding process is exothermic. The kinetics of the adsorption process indicated that the uptake of Pb(II) ions occurred within 40 min and that pseudo-second-order kinetics best describe the overall adsorption process.