摘要:

AbstractMethods are given for the‘derivatisation’ of various of the components of epoxy resins: after fractionation by g.p.c. but before further analysis by h.p.l.c. or g.p.c.This paper describes the use of the following reagents for this purpose: concentrated HCl (to convert epoxy groups into chlorohydrin units); solid NaOH (to convert 1, 2‐chlorohydrin groups into epoxy units); phenol (to open epoxy rings);N‐methylaniline (to open epoxy rings); and KMnO4(to oxidise —CH2— and — OCH2CHOHCH2O —

ISSN:0007-1641    

DOI:10.1002/pi.4980150112

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractThis paper first discusses the principles of Inelastic Electron Tunnelling Spectroscopy (IETS) and describes the experimental procedures needed to obtain spectra. Spectra are presented for an epoxide resin and two aliphatic amine‐hardeners, and for epoxideamine mixtures both before and after a heat curing schedule. From the latter it can be seen that the normal curing reaction between amine and epoxide groups does not take place within an IETS junction. A possible reason for this is the adsoprtion of amines onto the aluminium oxide surface of the substrat

ISSN:0007-1641    

DOI:10.1002/pi.4980150113

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractPositrons which annihilate with electrons in solids usually give rise to two gamma rays, each with an energy close to 0.511 MeV, which are emitted in almost exactly opposite directions. The spread of the energies about the nominal value, which amounts to a few keV, is a Doppler effect reflecting the velocities along the direction of gamma emission of the electrons with which the positrons happen to annihilate. Thus the shape of the annihilation line gives a weighted measure of the electron momentum distrubution, emphasising the conduction electrons and the loosely bound localised electrons. The Positron Annihilation Techniques (PAT) allow this distribution to be determined non‐destructively, and lend themselves to comparative measurements. If some of the positrons are trapped at negatively charged sites within a solid the annihilation radiation will reflect both the changed momentum distribution of the electrons seen at the trapping sites and the relative number of positrons which are trapped at the time of annihilation. To be effective the traps must have a mean spacing<100 nm, but the sensitivity of PAT to atomic scale traps such as vacancies can nevertheless be very high. Finally, in materials containing few free electrons, information can be extracted from the formation of the positron analogue of the hydrogen atom, positronium.With standard positron sources probing depths in plastics can be a few millimetres. The PAT techniques have already proved their worth in investigations of electron momentum distributions in ordered solids, and in investigations of phase changes and of mechanical and fatigue damage in metals and alloys. Their out‐of‐the‐way combination of characteristics makes them well worth consideration in other materials applications when conventional techniques run into diffi

ISSN:0007-1641    

DOI:10.1002/pi.4980150114

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractOptical microscopy with ultra‐violet illumination has been used to monitor the curing reactions and final structure of an amine‐cured epoxy resin system. When low concentrations of u.v. absorbing additive are added to the resin before curing, the additive is usually completely uniformly distributed in the cured product. No density variations on a scale resolvable in optical microscopy are visible. Similarly when a u.v. absorbing eragent is allowed to diffuse into the cured resin its diffusion profile is normal and shows no detectable density fluctuations in the resin. Reaction of cured resins with a reagent which couples with amino groups to give u.v. absorbing adducts shows that conventional hand mixing techniques do not produce complete mixing of the resin components and spatially non‐uniform concentrations of unreacted amines are found. This effect can only be removed by unusually thorough mixing techniques. Use of a water soluble u.v. absorber allows penetration of the epoxy by water to be followed. In particular, the penetration of fibre‐matrix interfaces by water can be vis

ISSN:0007-1641    

DOI:10.1002/pi.4980150115

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractThe use of a range of additives is described which can increase the strength and modulus of cured epoxy‐amine systems by up to 70 per cent. These additives, called ‘Epoxy Fortifiers’, are liquids or low melting point solids which are incorporated into the resincuring agent mixture, prior to curing, at loadings of 10–40 parts per hundred o

ISSN:0007-1641    

DOI:10.1002/pi.4980150116

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractPhase separation of polyethersulphone from solution in epoxy resins has been studied as a function of polyethersulphone concentration, type of resin, and curing conditions. The resins chosen were a rapidly curing tetrafunctional and a trifunctional epoxy resin, hardened with either diaminodiphenylsulphone, or dicyandiamide. Fracture surfaces of some of the cured blends exhibited nodular features between 0.2μm and 6μm in diameter. Using X‐ray microanalysis and scanning electron microscopy these nodules were shown to contain high concentrations of polyethersulphone. Mechanical properties, including fracture energy, dynamic mechanical relaxation and creep, were studied for the same range of blend compositions. Dynamic mechanical spectra provided further evidence for phase separation in certain blends, while elastic modulus, fracture toughness and creep showed little dependence upon composit

ISSN:0007-1641    

DOI:10.1002/pi.4980150117

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractCombinations of phenolic resols with high molecular weight thermoplasts in the form of aqueous dispersions can be prepared by dissolving the thermoplast in the phenol and reacting with aqueous formaldehyde solution in the presence of emulsifiers. The scope of this procedure has been explored and the wide variety of thermoplasts that can be utilised is demonstrated. Several of the products from this process show promising results in metal‐bonding applications. Some of the physical and chemical changes taking place during the reaction and dispersion are describe

ISSN:0007-1641    

DOI:10.1002/pi.4980150118

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractIn recent years a new generation of advanced structural adhesives has become available. They are typically based upon epoxy resins modified by the presence of a second phase of dispersed rubbery particles. This multiphase microstructure results in the material possessing a considerably higher toughness or crack resistance, compared to the unmodified, single‐phase resin, but with only a minimal reduction in other important properties such as modulus and high‐temperature and creep resistance. Even more recently, polyimide adhesives have also been toughened employing this principle.The present paper considers the following aspects:1The chemistry of rubbery‐toughened thermosetting polymers developed for adhesive applications.2Structure‐property relationships of multiphase adhesives which incorporate a dispersed rubbery phase or rigid particulate fillers. The mechanisms of toughening are discussed and related to the microstructure. The effects of volume fraction, particle size and particle size distribution on the polymer's fracture energy are also described3The particular problems encountered when using such toughened multiphase adhesives in structural joints are reviewed, including aspects of joint design and environmental

ISSN:0007-1641    

DOI:10.1002/pi.4980150119

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980150101

出版商:John Wiley&Sons, Ltd    

年代:1983

数据来源: WILEY