M.E.A. Cudby

The effect of cooling rate upon the morphology of quenched melts of isotactic polypropylenes

Abstract Experimental data are provided on the molecular structure of paracrystalline samples of quenched melts (glasses). We propose that rods of helical molecules are present in the ‘glasses’, their length being sensitive to the temperature of the melt from which the ‘glass’ is produced, the amount of time held in the melt and the rate of quenching. A comparison is made between samples crystallized from the melt and those crystallized via the glassy phase. By measuring the lamellar thickness, from Raman spectroscopy, and calculating the absorbance ratio A 998 A 973 from infra-red spectroscopy, longer helical sequences were shown to exist to a greater extent in the samples crystallized from the melt. Samples crystallized from the glassy phase contained shorter helical sequences. In investigating the effect of the surrounding temperature on solid polypropylenes, we have shown that the density of the material can be related to the temperature of storage. We comment on the relevance of this observation to dimensional stability in mouldings.

On the vibrational assignment problem for polytetrafluoroethylene: 1. The far infra-red spectrum

Studies of the polarized far infra-red spectra of drawn specimens of polytetrafluoroethylene (PTFE) and of the spectrum of the oligomer C14F30 both at room and liquid nitrogen temperatures have given results which strongly confirm the general form of recently published dispersion diagrams. However the absolute values of band intensities and their variation with specimen morphology suggest that some minor changes to the optical intersections are necessary. Intensity arguments also strongly indicate that the labelling, adopted by most recent workers, for the branches B6 and B7 should be interchanged.

Analysis of acoustic emissions from polymers

Abstract Acoustic emissions obtained from polymers under stress have been subjected to various mathematical analyses with the objective of relating the observed signals to accompanying chemical and physical changes in the polymer. The following methods have been investigated: frequency analysis, autocor-relation analysis, cepstrum analysis and cluster analysis (pattern recognition). It is shown that it is possible to classify the signals from a given polymer sample into relatively few types and that there is a periodicity in a number of plots of acoustic power vs time. Differences between samples are evident, although it is not possible at this stage to state that they are statistically significant. The materials examined include, nylon-6,6, ‘Diakon’, polypropylene and various composites.

Liquid-lattice type absorption in ethylene-vinyl acetate co-polymers

Abstract Far infrared and millimetre wave spectra of some dilute vinyl acetate-ethylene copolymers have been observed at room and liquid nitrogen temperature. Broad absorption bands below 100 cm −1 are attributed to liquid-lattice or Poley absorption. For very dilute co-polymers at liquid nitrogen temperature the 78 cm −1 band of crystalline polyethylene is discernible.

Acoustic emission and e.s.r. studies of polymers under stress

Abstract A nearly noise-free apparatus for the stressing of polymers is described. It has been used, in conjunction with a sensitive piezo-electric transducer and associated apparatus for the generation, detection and collection of acoustic emissions, from stressed polymers. It is shown that detectable levels of acoustic energy are released from several polymers and composites, and that the distribution of acoustic events varies with material examined. Parallel experiments have been carried out in which free radicals are generated by stressing bulk polymer in the cavity of an e.s.r. spectrometer. There is some correlation between stress and both acoustic emissions and free radical generation.

Polarized far infra-red studies of hot-drawn polytetrafluoroethylene

Abstract The three strong sharp lines in the 50 cm−1 region of the infra-red spectrum of polytetrafluoroethylene (PTFE) at liquid nitrogen temperature, have been shown to be strongly polarized, with the transition moments lying perpendicular to the molecular axes. This result is interpreted in terms of the lattice-mode theory and in terms of possible symmetries for the unit cell.

Far infrared and microwave absorption in ethylene-vinyl acetate copolymers

Abstract Further evidence is presented that the broad band, near 70 cm −1 for ethylene-vinyl acetate copolymers, is due to Poley-type absorption. A new band has been observed at 232 cm −1 which is tentatively assigned to an internal mode of the acetate group. The microwave dielectric loss is virtually independent of frequency which indicates that the underlying absorption mechanisms must be complex.

A new far infra-red absorption band at 39 cm−1 in the spectrum of high-pressure crystallized polyethylene

Abstract High-pressure annealed samples of polyethylene (PE), currently thought to contain the extended chain form, show a new band at 39 cm −1 in the absorption spectrum when the sample temperature falls below 170K. This band shows a strong temperature dependence of intensity but no shift in frequency as the temperature varies. Possible assignments of the band are discussed. The preferred interpretation, with some reservations, is that it arises from a mode analogous to the forbidden A u mode of orthorhombic PE but which is now active in the monoclinic form produced by the annealing.

Structure of crystalline polymers produced by rapid cooling of their melts: 2. Polyoxymethylene

Abstract The influence of the structure of motlen high density polyethylene on that of the crystalline material produced by rapid cooling of this melt has been investigated by Raman spectroscopy. It is shown that a relationship exists between the characteristic dimensions of a molecule in the molten phase and the length of the all trans linear sequences present in the subsequent crystalline material. The observations reported here are shown to be incompatible with the folded-chain lamellar structure often proposed for melt crystallized material; and an alternative model, in which the chains meander through neighbouring lamellae, is supported.

Thermal degradation of PTFE studied by ultraviolet photoelectron spectroscopy (u.p.s.)

Abstract The early stages of the thermal degradation of PTFE were followed by ultraviolet photoelectron spectroscopy in order to evaluate the technique and to establish the effects of changes in molecular weight and sample thickness, also γ-irradiation and copolymerization on the degradation reaction. The rate of decomposition and the concentration—time profile for the evolution of monomer from homopolymers was that predicted for a first order reaction, and depended on sample weight and area. Copolymers and γ-ray irradiated samples showed some differences in products and rates.