Showing papers in "British Polymer Journal in 1979"
TL;DR: Differential scanning calorimetry (DSC) has been used in the study of a series of hydrogels in an attempt to correlate water binding and transport properties as mentioned in this paper.
Abstract: Differential scanning calorimetry (DSC) has been used in the study of a series of hydrogels in an attempt to correlate water binding and transport properties. DSC and oxygen transport studies were carried out on a series of styrene-2-hydroxyethyl methacrylate copoly-mers. The transport of dissolved oxygen through those copolymers that contained no freezing water was found to be negligible in comparison to those in which both freezing and non-freezing water was present. This correlates well with the observation that the dense layer of asymmetric cellulose acetate reverse osmosis membranes was found to contain little or no free water.
On this basis, the use of DSC in the design of a hydrogel that contains little or no freezing water (to promote salt rejection) with a reasonably high total water content (to maximise water flux) for use in reverse osmosis, is described. The resultant copolymer of acrylamide, methacrylic acid and styrene has a total equilibrium water content (30 per cent) that is twice that of a typical dense cellulose acetate used in reverse osmosis and a very low (< 1 per cent) freezing water content.
Examination of the fine structure of the melting endotherms and freezing exotherms associated with various hydrogels shows several interesting features which are interpreted in terms of the existence of a continuum of water states. These range from water that is unaffected by its polymeric environment to water (on average two or less molecules per monomer repeat unit) that is hydrogen bonded to functional groups in the polymer.
86 citations
48 citations
TL;DR: The inadequacies of current theories of crystallisation rates are discussed in this article, and a method suggested for quantifying the quality of crystallinity in polymeric material in terms of the averages of the lamellae thickness is suggested.
Abstract: Methods for determining the crystallisation characteristics of polymer by differential scanning calorimetry are discussed, particularly in terms of their limitations. Isothermal and non-isothermal crystallisation thermogrphs are analysed to determine crystallisation mechanism and compared with other techniques. The inadequacies of current theories of crystallisation rates are developed. Melting studies on oligomers and polymers are developed in terms of recent theories of melting, and a method suggested for quantifying the quality of crystallinity in polymeric material in terms of the averages of the lamellae thickness.
34 citations
TL;DR: The paper reviews the major developments published in the Patent literature over the last thirty years insofar as these reflect the evolution of the so-called anaerobic and cyanoacrylate adhesive types and the recent introduction of the ‘toughened’ acrylic adhesives.
Abstract: The paper reviews the major developments published in the Patent literature over the last thirty years insofar as these reflect the evolution of the so-called anaerobic and cyanoacrylate adhesives and the recent introduction of the ‘toughened’ acrylic adhesives.
Reaction mechanisms are postulated and the problems of formulation and production discussed in detail together with the performance characteristics of the individual adhesive types.
31 citations
TL;DR: In this paper, DSC shows a variety of potentially confusing curves that result from a coupling of instrumental-and sample-based rate effects, which can be used to give true glass temperatures that characterise the method of glass formation.
Abstract: The heat capacity of an amorphous polymer is insensitive to molecular and processing variables except in the glass transition region. Here DSC shows a variety of potentially confusing curves that result from a coupling of instrumental- and sample-based rate effects. The curves can be simply analysed to give true glass temperatures that characterise the method of glass formation.
31 citations
24 citations
TL;DR: In this paper, a new method, using the propagation expectation defined by Case, is presented to compute directly and simply the general expressions of average molecular weights for condensation polymerisation of polyfunctional monomers.
Abstract: A new method, using the propagation expectation defined by Case, is presented to compute directly and simply the general expressions of average molecular weights for condensation polymerisation of polyfunctional monomers. In particular, the weight average molecular weight in systems composed of monomers endowed with both A and B coreactive functional groups is derived.
20 citations
TL;DR: In this article, the effect of post-curing at an elevated temperature on the strength of lap-shear joints made with amine-cured epoxy resins was investigated.
Abstract: The work arose from the need to explain the beneficial effect of post-curing at an elevated temperature on the strengths of lap-shear joints made with amine-cured epoxy resins. Supermolecular structures were imaged by several electromicroscopy techniques, usually at 100,000 X. Three, if not four, stages of supermolecular structure were made visible. (i) A phase-contrast image of 1.3 to 2.1 nm diameter which are probably stacked residues of bisphenol A. The d-spacing seen in the diffracting mode of the microscope probably arises from within this structure. (ii) A nodular structure of ca. 5 nm. (iii) Aggregates of nodules of ca. 17 nm rising to 40 n m on post-cure. These dimensions were obtained from cumulative distributions of sizes based on photodensitometer records from the electron-micrograph negatives. Aggregate dimensions vary with curing agent and state of cure although minor variations occur with specimen preparation.
18 citations
TL;DR: In this article, an empirical equation based on time-temperature superposition determines cure time as a function of degree and temperature of cure, and the dependence of glass transition temperature on degree of cure and heat capacity measurements on the cured resin, are discussed.
Abstract: Rates and extents of cure at different times and temperatures are determined for a modified epoxy resin system and related to gel time measurements. An empirical equation based on time-temperature superposition determines cure time as a function of degree and temperature of cure. The dependence of glass transition temperature on degree of cure, and heat capacity measurements on the cured resin, are discussed.
16 citations
TL;DR: In this paper, the effect of various inorganic and organic additives on the crystallisation behavior of polyethylene terephthalate has been examined and various methods of mixing the polymer and additives were also investigated and one involving screw extrustion was finally adopted.
Abstract: An examination of the effect of various inorganic and organic additives on the crystallisation behaviour of polyethylene terephthalate has been made. Various methods of mixing the polymer and additives were also investigated and one involving screw extrustion was finally adopted. Crystallisation studies were carried out using Differential Scanning Calorimetry under dynamic and isothermal modes covering both normal and cold-crystallisation conditions. Using screw extrusion mixed material it was found that almost all additives produced some nucleating effect as indicated by an increase in the rate of crystallisation. In particular, sodium benzoate and sodium stearate (1 per cent w/w) had the greatest effect, decreasing the initial cold-crystallisation temperature and increasing the temperature of equivalent half-times of isothermal crystallisation, both by about 20°C.
14 citations
TL;DR: In this article, a series of green strength EPDM terpolymers has been examined by X-ray diffraction and thermal analysis and it has been found that the crystallinity of such materials can vary from 0.20% as measured by thermal analysis, and depends on the E:P ratio in the polymer.
Abstract: The crystallinity of a series of ‘medium-high’ green strength EPDM terpolymers has been examined by X-ray diffraction and thermal analysis. It has been found that the crystallinity of such materials can vary from 0.20% as measured by thermal analysis, and depends on the E:P ratio in the polymer. It is also suggested that it depends on the distribution of E and P units. An explanation for the differing results obtained by thermal analysis and X-ray diffraction has been proposed. The time taken to achieve maximum crystallinity varied for the series of polymers examined, and the improvement of crystallites continued over extensive periods of time. The final level of crystallinity in the polymers and the rate of changes occurring was temperature dependent. For one sampel (‘Nordel’ 1560) it was shown that crystallinity affected mechanical properties.
TL;DR: The influence of residual styrene monomer and benzaldehyde on the surface properties of polystyrene latices has been considered in this paper, where controlled experiments with a latex dosed with various levels of a penicillium type fungus demonstrated the possibility that enzymes (classified as aryl sulphate sulphohydrolases - E. C. 3.1.6.1.) were produced which resulted in the rapid hydrolysis of surface sulphate groups.
Abstract: The influence of residual styrene monomer and benzaldehyde on the surface properties of polystyrene latices has been considered. These materials are commonly found after emulsion polymerisation and their complete removal by dialysis is almost impossible. Steam stripping at reduced pressure (nitrogen atmosphere, < 350K) can be used to remove the last traces of styrene and benzaldehyde from polystyrene, but this process results in some degree of hydrolysis of the surface sulphate groups.
Latices are easily contaminated by microorganisms, especially those which are airborne. This can occur during cleaning and/or storage. Microorganisms can survive and multiply in suitable latex environments and can result in the destabilisation and subsequent flocculation of the latex. Controlled experiments with a latex dosed with various levels of a penicillium type fungus demonstrated the possibility that enzymes (classified as aryl sulphate sulphohydrolases - E. C. 3.1.6.1.) were produced which resulted in the rapid hydrolysis of surface sulphate groups. Fungal growth was accompanied by the release of weak acids and metabolites which were titrated in the aqueous phase.
Careful consideration should be given to the conditions of latex preparation, cleaning and storage, e.g. use of autoclaved water and γ-irradiation techniques, which will reduce the possibility of microbial contamination. Routine tests for bacteria and fungi should be carried out by plating on microbiological media, since the usual tests for protein such as the Folin-Ciocalteu are insensitive at the low levels of contamination which may be present.
TL;DR: In this paper, the scope of thermal methods and their application to polymeric substrates are reviewed and the general application of these methods to polymers is discussed and illustrated by reference to the problems associated with thermal methods.
Abstract: The scope of thermal methods and their application to polymeric substrates are reviewed. The general application of these methods to polymers is discussed and illustrated by reference to: (i) the problems associated with thermal methods and the apparatus used to obtain thermal responses; (ii) the problems associated with calibration and the standardisation of reporting procedures; (iii) the specific problems associated with polymeric materials. Problems associated with crystallinity determinations and thermal stability assessment are also discussed.
TL;DR: In this paper, a new method is proposed for extrapolating light-scattering data to the zero angle of scattering, which consists of iterative extrapolations by use of the regression method as a subroutine, and applies in general to the data obtained at low polymer concentrations and at low angles of scattering.
Abstract: A new method is proposed for extrapolating light-scattering data to the zero angle of scattering. Essentially the method consists of iterative extrapolations by use of the regression method as a subroutine, and it applies in general to the data obtained at low polymer concentrations and at low angles of scattering. Light-scattering results on high molecular weight linear polystyrene in benzene were successfully analysed with the method. In comparison with other published methods, the strong points and limitations of the method are discussed.
TL;DR: The application of ultraviolet and fluorescence microscopy to polymers usually depends upon the use of some form of staining reagent to develop contrast within the polymer and three variations of this principle are described in this article.
Abstract: The experimental requirements for ultraviolet and fluorescence microscopy are briefly discussed. The application of these techniques to polymers usually depends upon the use of some form of staining reagent to develop contrast within the polymer and three variations of this principle are described. In the first, ultraviolet absorbing or fluorescent additives are monitored during spherulitic crystallisation of a polymer with quantitative results which demonstrate rejection of the additive by the crystalline polymer and allow the diffusion coefficient for the additive in the molten polymer to be estimated. In the second application, the equilibrium distribution of absorbing additives after crystallisation is used to reveal crystallinity variations within the sample and to study the influence of non-crystallisable fractions upon these variations. Finally, reaction of carbonyl groups, with fluorescent or absorbing reagents, in oxidised polymers, has been investigated as a way of revealing uneven oxidation in polypropylene.
Abstract: For light scattering analysis of an extremely high molecular weight polymer with large size in solution, use of mixtures of a given polymer with its low molecular weight homologue is described to have great advantages. With such bimodal mixtures as test samples, one can alter the unknown form of the angular variations of scattered lights to a form to be expected and widen the range of the linearity with sin2 (o/2), where o is the scattering angle. According to the considerations, a sample of linear polystyrene was successfully analysed on a commercial apparatus, Fica 50 to have the weight-average molecular weight of 27 million.
TL;DR: In this paper, the Young's Modulus of PVC plasticized with various dialkylphthalates at concentrations from 40-120 phr that has been subject to a short heat treatment at 100°C, increases linearly with the logarithm of the time of storing at temperatures from 20-100°C.
Abstract: The Young's Modulus of PVC plasticised with various dialkylphthalates at concentrations from 40–120 phr that has been subject to a short heat treatment at 100°C, increases linearly with the logarithm of the time of storing at temperatures from 20–100°C. Both the Young's Modulus and its rats of increase with time is found to increase with increasing size of plasticiser to increase with decreasing concentration of plasticiser and to pass through a maximum with changing temperature of storage at a temperature of about 38°C. These effects can be explained if it is assumed that the elasticity results from a network linked by crystallites that can be melted on heating and reformed on storing at a lower temperature. The density of the plasticiser compositions is found to increase with time and this together with the development of endothermic DSC peaks support the hypothesis that changes in rigidity result from changes in crystallinity. The endothermic peak occurs at an almost constant temperature independent of plasticiser concentration or the size of the plasticiser molecule. It is suggested that the effect of these variables on the the melting point is nullified by the changes they also produce in crystallite size.
TL;DR: In this article, the authors examine some of the scientific topics that contribute to the present day knowledge of high strength adhesives and that are now used when advances are sought in the technology.
Abstract: Epoxide resins were introduced commercially thirty-three years ago. One of the first formulations was an adhesive. There has been continuous development of the systems since then based on an increasing range of materials used in their constitution and an increasing knowledge of their chemistry and cured properties. This paper examines some of the scientific topics that contribute to the present day knowledge of these high strength adhesives and that are now used when advances are sought in the technology.
TL;DR: In this paper, an extrapolation method is proposed using the newly defined average molecular weights at a given radial position to cope with poly disperse materials such that fringes become unresolvable near the cell bottom.
Abstract: In view of the recent advances in the theory of sedimentation equilibrium, the meniscus depletion is reformulated and extended to reveal its potentialities. To cope with poly disperse materials such that fringes become unresolvable near the cell bottom, an extrapolation method is proposed using the newly defined average molecular weights at a given radial position. The main purpose of the method is to pave the way for determining the number-average molecular weight of a sample. Its applications to a linear polystyrene sample having the weight-average molecular weight of twenty seven million are reported in this paper. Uses and limitations of the present method are discussed in detail.
TL;DR: In this paper, a review of factors which govern the effectiveness of materials as adhesives is presented, starting with the forces available for adhesion, the roughness of surfaces, and the wetting and flow properties of liquids.
Abstract: Review of factors which govern the effectiveness of materials as adhesives. Begins with the forces available for adhesion, the roughness of surfaces, and the wetting and flow properties of liquids. Then the necessary phase change is considered and finally these requirements are correlated with actual classes of material.
TL;DR: Gelatine gel samples formed in contact with phases of various polarity such as glass, plexiglass (PMMA) and air have been studied by a Roth-type micro-penetrometer as mentioned in this paper.
Abstract: Gelatine gel samples formed in contact with phases of various polarity such as glass, plexiglass (PMMA) and air have been studied by a Roth-type micro-penetrometer. The experimental results showed that the penetrability of the gels was significantly effected by the adjacent phase. Comparing the data with those found on a freshly cut surface representing the bulk of the gel it can be assumed that the differences are caused by different orientation of the gelatine molecules in the penetrated region. In order to prove this assumption gels containing sodium chloride, sodium sulphate and sodium dodecyl sulphate, respectively were prepared. It has been shown that the rigidity of the gel/air surface and that of the bulk was effected similarly but not equally by the salts.
In order to learn the processes occurring in presence of the above mentioned cosolutes turbidity measurements were carried out on all samples using a Pulfrich nephelometer.
TL;DR: In this paper, a copolymer series was synthesized for migration imaging applications from isobutyl methacrylate and poly styrene such that each homopolymer and all copolymers had glass transition temperature (Tg) near 55°C.
Abstract: A copolymer series was synthesized for migration imaging applications from isobutyl methacrylate and isobutyl styrene such that each homopolymer and all copolymers had glass transition temperature (Tg) near 55°C. The Tg of poly (p-isobutylstyrene) was predicted from literature values of similar polymers to be near 55°C. Poly (p-isobutylstyrene) was synthesised by acetylation of isobutyl benzene, reduction of p-isobutylacetoph-enone to the carbinol, dehydration to p-isobutylstyrene and free radical polymerisation to the polymer. The Tg of the homopolymer was 55°C, in excellent agreement with the predicted value. Copolymers of isobutyl methacrylate and p-isobutyl styrene were synthesised and their Tg's measured across the series by DSC (57°C ± 5°C). refractive index temperature coefficient (42°C ± 5°C). The copolymer series was also characterised by melt viscosity measurements.
TL;DR: The trimethylsilylation of pseudowollastonite gives a polyorganosiloxane (Mn, 890) as discussed by the authors, which can be further converted to a series of organic derivatives, which are capable of further reaction to give higher molecular weight homologues.
Abstract: The trimethylsilylation of pseudowollastonite gives a polyorganosiloxane (Mn, 890). The aim of this work was to increase the molecular weight of this initial or pre-polymer and to bond into the molecule further functional groups. The methyl groups of the trimethylsilyl moiety have been converted to a series of organic derivatives: -> Si(CH3)2CH2X; × = C1, Br, I, Ac, OH: which are capable of further reaction to give higher molecular weight homologues. As expected the ->Si(CH3)2CH2OH group reacts readily with chlorosilancs whilst the original pre-polymer hydroxyl groups give disappointing yields in these and other reactions owing to their sterically hindered environment.
TL;DR: In this paper, it was shown by using wet analytical techniques as well as X-ray diffraction and electron probe microanalysis that biotite and phlogopite retain aluminium in preference to magnesium during the course of extensive trimethylsilylation reactions.
Abstract: The trimethylsilylation of biotite and phlogopite gives good yields of polyorganosiloxanes. Al3+ ions have an important influence on the fragmentation of the mineral structure into silicate anions prior to trimethylsilylation.
The authors have shown by using wet analytical techniques as well as X-ray diffraction and electron probe microanalysis that biotite and phlogopite retain aluminium in preference to magnesium during the course of extensive trimethylsilylation reactions. The labile nature of the >Al-O-Si<- bonds, and the size of the AI3+ ion which allows exchange between the octahedral and tetrahedral mineral sites, contribute to the good yields of polyorganosiloxanes which can be produced by this method. The mechanism for the reaction is presented. Yields may be increased by decreasing the particle size of the mineral and also by removing polyorganosiloxanes from the mineral surface.
TL;DR: In this article, the thermal stability of polyorganosiloxanes derived from pseudowollastonite in closed systems in the presence of acid/base catalysts is also reported.
Abstract: The polyorganosiloxanes prepared by the trimethylsilylation of mineral silicates contain Q [SiO4/2] units and M [CH3)3 SiO1/2] units. Investigations into the behaviour of these materials in the temperature range 100-1000°C and for times varying from 2-64 hours have shown that a variety of reactions take place with a general increase in number average molecular weight (Mn). Organophilic polyorganosiloxanes with Mn > 6000 can be obtained by heat treatment under vacuum or a stream of nitrogen. The thermal stability of the polymer derived from pseudowollastonite in closed systems in the presence of acid/base catalysts is also reported. This work is part of a general programme to prepare higher molecular weight Q/M polymers with more potential uses as industrial materials than the initially prepared trimethylsilylated derivatives.