摘要:

AbstractThe tapered cantilever cleavage and the single‐edge‐notch tension fracture toughness tests have been shown to give similar results for several cured epoxy resin systems. Methods for the calculation of fracture energy and critical stress intensity factors are described and discussed. These tests have been used to study the influence of rubber modifiers (“Hycar” CTBN and “Blendex” 311) on the toughness of a conventional epoxy resin (“Epikote” 828) reacted with anhydride curing agents. The modifiers used increase fracture energies and stress intensity factors by factors of approximately 5 and

ISSN:0007-1641    

DOI:10.1002/pi.4980070102

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractA study of the phosphorescence emission from the commercial polyolefins, polyethylene, polypropylene and poly‐4‐methylpentene‐1 and the polyamides, nylon 6/6, 6, 11 and 12 is presented and the origin of the emission discussed. Impurity centres in the polymer are responsible for the emission, being present either as groups directly attached to the polymer backbone or as discrete molecules within the polymer matrix. These impurities can play an important part in the thermal and photochemical oxidation of the polymer. Therefore, changes in the phosphorescence spectra can provide valuable information on the mechanisms of both degradation proc

ISSN:0007-1641    

DOI:10.1002/pi.4980070103

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractSeries of polystyrene and polymethyl methacrylate latex dispersions have been prepared in the absence of any surfactant using potassium persulphate as an initiator. The latex particles are stabilised by the electrical repulsion generated by the sulphate groups which are covalently linked to the polymer molecules and are not removed by dialysis. The effects of polymerisation temperature, monomer concentration and initiator concentration on the ultimate particle size and conversion were investigated for these two series of lattices. The modal diameters of these lattices were found to be in the range of 530 to 1550 nm for polystyrene lattices, and 140 to 270 nm for polymethyl methacrylate lattices. The surface charge densities were calculated from conductometric titration results for polymethyl methacrylate lattices and were found to increase almost linearly with increase of the concentration of potassium persulphate used.

ISSN:0007-1641    

DOI:10.1002/pi.4980070104

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractThe physicomechanical properties and processes of thermal crosslinking of latex acrylic polymer films containing functional groups of different chemical nature were studied. Improvement of properties characteristic of latex copolymers containing methylolamide groups is explained by orientated location of hydrophilic groups on the surface of latex particles during emulsion copolymerisation, that, in its turn, leads to a more ordered arrangement of macrochains. An optimum content of methylolamide groups as regards crosslinking processes was established and explained by steric location of these groups on the surfaces of latex particles. A similar optimum is not observed for crosslinking by watersoluble resin of latex copolymers containing groups of hydrophobic glycidylmethacrylate.

ISSN:0007-1641    

DOI:10.1002/pi.4980070105

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractGlass forming high polymers have been densified by application of high hydrostatic pressure (∼1.5 kbar) in the melt followed by cooling under pressure to ambient. A density increase of about 1% was induced in each of the following polymers: polyvinylchloride, polymethylmethacrylate, polystyrene, poly‐4‐chlorostyrene, poly‐3‐chlorostyrene, poly‐4‐methoxystyrene and poly‐4‐phenoxystyrene. Differential thermal analysis (DSC) and volume relaxation techniques were used to study the reversion of the densified glass to a more normal glass at a temperature ∼Tg– 15 K in general. Enthalpy relaxation (a change from glass I to glass II) in this region gives a peak or diffuse hump on the DSC scan prior to a normal glass transition temperature. It is considered that although the densified glasses may become thermodynamically stable at a sufficiently low temperature they are inherently unstable at ambient. Reversion to a more normal glass is kinetically too slow to measure at ambient in all cases studied except polymethylmethacrylate. Changes of dynamic Young's moduli and dielectric constant with densification are reported in detail for some systems and in summary for others. The densified glasses exhibit moduli higher by ∼6%, dielectric constant higher by ∼2% and depressed secondary mechanical and dielectric relaxation processes. Ultimate property stu

ISSN:0007-1641    

DOI:10.1002/pi.4980070106

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980070108

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980070109

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980070101

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY