ISSN:0258-0322    

DOI:10.1002/masy.19890280103

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe paper will give a short introducing survey on the present state of polyolefin and copolyolefin cross linking.The combination of high‐density polyethylene (PEHD) and polypropylene (PP) with elastomers, particularly with ethylene‐propylene terpolymer (EPDM), results in high‐impact strength PP (HI‐PP) and in thermoplastic elastomers (TPE) considered as high‐performance polyolefin composites (HP‐POC). By filling of PEHD and PP, HP‐POCs with increased stiffness, modulus, and abrasion resistance can be produced. They are cost ‐ advantageous substitutes for construction materials as, for example, ABS. Possibilities and limits are demonstrated by own investigations in this field.Best mechanical properties are obtained by reinforcement with fibres, particularly with glass fibres. Requirement for superior parameters is a chemical coupling between glass‐fibre surface or glass‐fibre size, respectively, and the PP matrix.A new adhesive agent on the basis of siloxane allows to reach high strength and toughness of the composites. The effect seems to be due to a better mutual penetration of the adhesive agent, the size, and the PP matrix. Outlooks will be given on the further development of HP‐POC in the field of reinforcement and reactive combinatio

ISSN:0258-0322    

DOI:10.1002/masy.19890280104

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe problems of ionic coordination polymerization of higher α‐olefins are summarized briefly. During the polymerization such monomers as 3‐methyl‐butene‐1, vinylcyclohexane and others isomerize into unreactive isomers, and the rate of polymerization and final yield of polymer are sharply decreased as compared with the polymerization of lower olefins. The modification of polypropylene by ionic coordination copolymerization of propylene with higher α‐olefins and polar monomers is considered. Significant modification of carbochain polymers may be obtained by the insertion of heteroatoms in the backbone. New possibilities for chemical “modification” of olefins by direct interaction with sulphur and the unusual aspects of the polymerization of olefin sulfides are also considered. The subsequent transformation of polyolefin sulfide gives polymers which have properties drastically differing from those of polyolefins. In conclusion, some new application area

ISSN:0258-0322    

DOI:10.1002/masy.19890280105

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe limitations of conventional antioxidants and stabilisers in polymers are associated with their migration into contacting fluids. This leads to toxicity in packaging and medicinal applications and loss of effectiveness in many engineering uses of polymers. Reactive processing procedures are being increasingly used to chemically attach antioxidants to polymers and the most successful of these involve the synthesis of bound antioxidant concentrates which can be used as macromolecular adducts for normal polymers. Present evidence suggests that a polymer modified by substantial concentration of antioxidants loses its physical identity and can be used in a range of other polymers. Future developments in which the additives are 100% bound to the polymer substrate are discussed.

ISSN:0258-0322    

DOI:10.1002/masy.19890280106

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe melting behaviour of gelspun/drawn UHMW‐PE and UHMW‐PP fibres was investigated. Unconstrained UHMW‐PE and UHMW‐PP fibres melt at 142°C and 170°C, respectively. Upon constraining, by holding the fibres at a fixed length or by embedding the fibres in a matrix, an increase in the melting temperature of both fibres is observed. In the case of UHMW‐PE fibres a solid‐solid phase transition in polyethylene at 155°C from the orthorombic to the hexagonal crystal structure occurs. Above 155°C, the fibres can not sustain any load. This solid‐solid phase transition at 155°C sets an upper limit to both the maximum curing and continuous use temperature of PE‐fibre reinforced composites. In gelspun/drawn UHMW‐PP, such a detrimental solid‐solid phase transition is absent, and therefore the increase in melting temperature can be utilized effectively. For example, heating of UHMW‐PP fibres for 30 minutes at 200°C does hardly affect the room temperature Young's modulus and tensile strength if the fibre is

ISSN:0258-0322    

DOI:10.1002/masy.19890280107

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractPecularities of deformation of two‐phase blends is considered depending on drawing conditions and mechanical properties of each phase.Significant anisotropy of mechanical properties of polymer blends film can take place because of particle orientation of dispersed polymer. This significant anisotropy exists also when there is no orientation of macromolecules in each phase. Possibility is demonstrated to regulate properties of each phase in polymer blends by addition of selective plasticizer which can act only on one polymer phase in two‐phase polymer mixt

ISSN:0258-0322    

DOI:10.1002/masy.19890280108

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThree problems of the radiation modification of polymers are dealt with. Different methods of grafting are compared with respect of the formation of true graft copolymer and homopolymer in the polyethylene‐styrene system; the prevention of the penetration of monomer by grafting polytetrafluoroethylene is shown; the mechanical properties of crosslinked ethylene polymers below and above the melting point are discusse

ISSN:0258-0322    

DOI:10.1002/masy.19890280109

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractAs a result of studying the interaction of hindered amine stabilizers (2, 2, 6, 6‐tetramethylpiperidines) with simple hydroperoxides, peroxy radicals, and acylperoxy radicals, the last two in AIBN‐initiated oxidation experiments in chlorobenzene, the following conclusions have been reached:1Hindered amines have multiple mechanisms of functioning as photostabilizers of polymers.2Reactions between tetramethylpiperidines and simple hydroperoxides are too slow at moderate temperatures to make a significant contribution to polymer stabilization.3Reactions between tetramethylpiperidines and alkylperoxy radicals at moderate temperatures occur at varying rates with varying effectiveness for stabilization. With favorable alignment among reaction rates for oxidation propagation and termination, reactions between tetramethylpiperidines and alkylperoxy radicals can play a significant role in oxidation inhibition.4Hydrocarbon polymer photooxidation proceeds by two major paths ‐ the usually accepted alkyl radical/alkylperoxy radical/hydroperoxide route and the usually neglected aldehyde/acyl radical/acylperoxy radical/peracid route.5Hindered amine stabilizers are able to participate in inhibiting both photooxidation reactions ‐ they trap acylperoxy radicals, converting them to carboxylic acids and are converted to nitroxyl radicals in the process; the nitroxyl radicals trap alkyl radicals and the hindered amines trap alkylperoxy radicals to inhibit the other oxidation pathway.6Nitroxyls are regenerated from N‐alkyloxy hindered amines in a fast, efficient reactions with acylperoxy radicals and in slow reactions with alkylperoxy radicals. We postulate neither reaction yields peroxides: carboxylic acids and oxidized alkyloxy substituents are obtained from the first reaction; alcohols and oxidized alkyloxy substituents are obtained from the second

ISSN:0258-0322    

DOI:10.1002/masy.19890280110

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractWe review some of the available evidence to suggest that the oxidation of polypropylene is not a homogeneous process but is localised at several levels. Optical microscopy of oxidised polymer shows regions of high oxidation on the micron scale, sometimes associated with uneven distribution of catalyst residues. Atactic polymer is shown to oxidise more rapidly than isotactic and to be redistributed in the isotactic polymer during melt crystallization. Atactic polymer is shown by GPC to undergo random scission with the formation of terminal carbonyl groups; in contrast, the oxidation of isotactic polymers is non‐random. Finally, evidence is discussed to show that both the initiation of oxidation by peroxide decomposition and its termination by radical recombination follow complex kinetic

ISSN:0258-0322    

DOI:10.1002/masy.19890280111

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractPolyolefin composites were prepared with CaCO3fillers of different specific surface area. The fillers were surface treated with stearic acid between 0 and 100% surface coverage. As an effect of the treatment, surface tension of the fillers and also polymer/filler interaction decreased. The relation between interfacial interaction and mechanical properties of the composites was analysed by the equation developed earlier to describe the composition dependence of the tensile yield stress. The characteristics of the interphase were calculated, its yield stress decreases and thickness increases with increasing surface coverage. Reversible work of adhesion can be successfully related to the tensile yield stress, but a more complicated correlation exists between the thickness of the interphase and the strength of the interaction than assumed earlier. Other mechanical properties also change with the surface treatment; modulus and strength decrease and extensibility increases with decreasing polymer/filler interaction.

ISSN:0258-0322    

DOI:10.1002/masy.19890280112

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY