Peter K. Fearon

Carbon nanotubes as polymer antioxidants

The oxidation of polystyrene, polyethylene, polypropylene and poly(vinylidene fluoride) is retarded by carbon nanotubes. Incorporation of boron into the nanotubes enhances the electron affinity of the tubes and leads to a small increase in antioxidant efficiency.

Evaluation of the oxidative stability of multiextruded polypropylene as assessed by physicomechanical testing and simultaneous differential scanning calorimetry-chemiluminescence

Common physicomechanical tests comprising impact strength, the melt flow index (MFI), and the yellowness index (YI) were used to study the thermooxidative stability of polypropylene (PP) following multipass extrusion. Differential scanning calorimetry (DSC) coupled with chemiluminescence (CL) monitoring was also used to assess the stability. Three PP formulations were studied: (i) PP-1 containing 0.050% w/w of the phenolic antioxidant Irganox 1010™, (ii) PP-2 containing 0.028% w/w Irganox 1010, 0.056% w/w of the phosphite costabilizer Irgafos 168™ and 0.014% w/w of the lactone processing stabilizer HP 136™, and (iii) PP-3 containing 0.050% w/w Irganox 1010 and 0.100% w/w of the phosphite Ultranox 641™. All formulations contained 0.045% w/w of the hydrotalcite acid scavenger DHT-4A™. The results suggest that physicomechanical tests cannot reliably detect the small difference in the stability between PP-2 and PP-3 but can detect the larger difference between these and the less stable PP-1. The oxidative induction time (OIT) determined by CL monitoring (i.e., CL– OIT) is consistent with the OIT determined by DSC but has better reliability. The CL–OIT data suggest that PP-3 has superior oxidative stability to PP-2 in the early stages of multipass extrusion. However, PP-2 exhibits a better resistance to yellowing. A correlation between the CL–OIT data and each of the MFI and YI data was found.

Tungsten Disulphide Sheathed Carbon Nanotubes

An insulated nanotube wire is formed by the binary phase of layered tungsten disulphide and carbon nanotubes (shown in the HRTEM image) generated by the sulphidization of tungsten oxide coated multiwalled carbon nanotubes at 900 °C. Thermogravimetric analysis shows that the tungsten disulphide coat acts as an antioxidant.

A new approach to quantitatively assessing the effects of polymer additives

A novel approach involving stability parameter mapping and stability vector analysis is developed for assessing the effect of an additive on polymer performance. The potential usefulness of the method is illustrated by applying it to (i) DSC oxidative induction time (OIt) data for medium-density polyethylene (MDPE) formulations made using two levels of carbon black and base-stabilized with Irgafos 168™ (tris-(2,4-di-tert-butylphenyl)-phosphite) and Irganox 1010™ pentaerythrityl-tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), and (ii) chemiluminescence OIt data for low-density polyethylene (LDPE) containing 0.2% (w/w) of Chimassorb 944™ and 0.5% (w/w) or 1.0% (w/w) of dicumyl peroxide cross-linking agent and base-stabilized with 0.2% (w/w) of various commercial antioxidants. The proposed method is validated using data from a previous study on MDPE and is applied to a preliminary investigation of LDPE destabilization by dicumyl peroxide. The results suggest that a styrenated phenolic stabilizer blended with zinc dibutyldithiocarbamate and zinc stearate is an effective system for stabilizing LDPE in the presence of dicumyl peroxide.

The second time derivative analysis of chemiluminescence emission profiles and its application to the accurate determination of oxidative induction times

The technique of second time derivative (STD) analysis is developed and applied to the chemiluminescence (CL) profiles of two polypropylene (PP) formulations and a 5% w/w blend of polybutadiene (PBD) in PP to assess this novel method of analysis as a means of reliably determining the oxidative induction time (OIT) of polymers. It is proposed that the STD technique, when used in conjunction with the integrated CL profile, can enable evaluations of the OIT to be made that are less subjective than those made using the conventional extrapolation method. This is particularly so in systems that exhibit a gradual onset towards autoacceleration and/or convoluted CL profiles. Chemiluminescence profiles of the PBD–PP blend that were obtained at different temperatures were subjected to STD analysis, and Arrhenius plots of the data were made. The results are consistent with the notion that the PBD and PP phases oxidize almost independently. The activation energies for the oxidation of the PBD and PP phases were calculated to be 200 ± 31 kJ mol−1 and 146 ± 9 kJ mol−1, respectively. The higher activation energy for the PBD phase is partly attributed to the greater partitioning of thermal stabilizer in this phase.

Binary Phase of Layered Nanotubes

A binary phase of layered nanotubes, where MWCNs (Multi-walled carbon nanotubes) are coated by WS 2 , are generated by pyrolysing WO 3 -coated MWCNs in an H 2 S/N 2 atmosphere at 900 °C. TGA and TEM show that WS 2 acts as an antioxidant with respect to the MWCN core.