Andrew Garton

Molecular Orientation Measurements in Polymers by Infrared Spectral Subtraction

The data manipulation ability of a Fourier transform IR spectrometer is exploited to characterize molecular orientation in polymers. In particular, the application of spectral subtraction to dichroic ratio determination and to the measurement of three-dimensional orientation via sample tilting and internal reflection spectroscopy is explored for nylon film samples.

Infrared Spectroscopy of Polyethylene Terephthalate Fibers: Uses and Limitations

The potential of Fourier-Transform Infrared (FTIR) spectroscopy for characterizing polyethylene terephthalate (PET) fibers is examined both from a practical and a theoretical view point. Problems associated with sample preparation, spectral data analysis, and refraction and reflection at the fiber surfaces are discussed. The FTIR technique is used to characterize a range of partially-oriented PET fibers with differing fabrication histories and to determine the level of amorphous orientation in drawn PET fibers.

The stability of polymers in low earth orbit

Abstract Most organic polymers and some on polymeric materials such as silver or pigments suffer appreciable surface damage in the form of erosion or oxidation when exposed to the low earth orbit (LEO) environment encountered on shuttle flights. Surfaces facing the direction of flight suffer the most damage because of ram effects. Typical thickness losses for plastic films (eg. epoxy, Kapton, Mylar) can be 5 – 10μm. The aggressive chemical nature of the LEO environment (including atomic oxygen and O + ions), aided by the high collision energies of the gases with forward facing surfaces, are thought to be responsible for the erosion and oxidation.

The Photo-Oxidation of Polypropylene Monofilaments Part III: Effects of Filament Morphology1

The elongation-at-break of highly-oriented polypropylene monofilaments is much less affected by photo-oxidation build-up than undrawn or partially-oriented filaments. This appears to result from the very poor lateral cohesion of the fibril bundles in the highly-oriented filament, limiting restructuring and cracking to a thin surface layer. For less-oriented samples photo-oxidation-induced restructuring of the surface layer results in deep cracks that can propagate under stress, greatly embrittling the sample. Areas of filaments cold drawn by, for example, bending or stretching deteriorate very rapidly on uv irradiation as a result of strain-induced chromophore formation, and fracture occurs first at these points. Oxidation-product levels (either hydroperoxide or carbonyl) are shown to be an unreliable index of the extent of deterioration of mechanical properties resulting from uv exposure.

A spectroscopic study of the carbonisation of poly(acrylonitrile) and poly(acrylonitrile-co-acrylic acid)

Abstract The advantages and limitations of modern infra-red (ir) and solid state 13 C nuclear magnetic resonance (NMR) spectroscopic techniques are described for the characterisation of poly(acrylontrile) (PAN) and poly(acrylonitrile-co-acrylic acid) after various thermal treatments. The thermal treatments were chosen to model the pre-oxidation and carbonisation steps in the production of carbon fibres from PAN. Infra-red is particularly useful in following reactions of nitrile groups and the production of carbonyl species. Nuclear magnetic resonance spectroscopy is particularly valuable in following aromatisation processes. Both techniques are more limited by problems in spectral assignments than by difficulties in obtaining spectra. At high carbonisation temperatures (>500°C) 13 C NMR is restricted by the reduction in the amount of hydrogen available for the effective use of cross polarisation techniques.

Plasma etching of polypropylene films and fibres

The introduction of a ∼1000 Å scale corrugated structure, aligned perpendicular to the filament axis, into oriented semi-crystalline polymers on plasma etching is shown to result from restructuring of the partially etched surface and not, as has previously been proposed, to correspond to morphological detail in the unetched material. The detail exposed on plasma etching polypropylene is shown to vary extensively with the etching conditions used. The exposed surface is compared with those resulting from peeling and chromic acid etching. Plasma etching is, however, shown to be useful in exposing coarse morphological detail such as spherulites, and in providing a convenient route for rapidly stripping the polymeric sample. The restructured partially etched surface may then be removed easily by, for example, a brief chromic acid treatment, exposing the sample interior to microscopic examination.

Infrared spectroscopy of carbon-filled polymers

Application de la spectrometrie IR a reflexion interne a la caracterisation de caoutchoucs EPDM renforces de noir de carbone et de resines epoxyde charges de carbone

Far-infrared spectrum of poly(p-phenylene terephthalamide)

Abstract The polarized and unpolarized far-infrared (460-30 cm−1) spectra of poly(p-phenylene terephthalamide) (PPTA) fabric and fiber arrays are reported. These spectra are discussed and tentatively analyzed on the basis of the internal and external modes of the repeat unit of PPTA. To assist in band assignments, the spectra of potassium triiodide-treated PPTA fibers and of benzanilide and its benzene solution are also reported.

FT-IR of the Polymer-Reinforcement Interphase in Composite Materials

A modified internal reflection spectroscopy (IRS) technique is described, where the IRS element is coated with a thin (<100 nm) layer of a material intended to simulate the surface of a reinforcement. Examples of coatings include silica, poly(p-phenyleneterephthalamide), carbonized poly(acrylonitrile) and an aminosilane coupling agent. The way in which these surfaces affect the crosslinking kinetics and final crosslinked state of the first 200–400 nm of an amine- or anhydride-cured epoxy resin was then determined by infrared (IR) spectroscopy. Chemical differences detected by spectroscopy are shown to correlate with physical property differences of reinforced epoxy composites.