摘要:

AbstractTwo types of catalytic antioxidant are now recognised. The first involves the catalytic destruction of hydroperoxides to non‐radical products and the second consists of “stable” redox couples with the ability to remove both alkyl (CB‐A) and alkylperoxyl (CB‐D) radicals in autoxidising systems. The conditions under which both types of antioxidant can operate effectively are reviewed and the limitations to their activity are

ISSN:0258-0322    

DOI:10.1002/masy.19890270103

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe hydroperoxides produced by thermal oxidation of LDPE films were used to study their photolysis. Product analysis, kinetics of hydroperoxide decomposition and product formation as well as experiments with model compounds point to new mechanisms of hydroperoxide photolysis. Intermolecular as well as intramolecular decomposition mechanisms are proposed. In polyethylene, these reactions are essentially non‐initiating. In addition, it is confirmed that ketones such as those formed by oxidation of polyethylene do not have a significant initiating effect. Reactions of excited charge‐transfer complexes polyethylene‐oxygen are proposed to account for initiation of photo‐oxidation. One of these reactions yields trans‐vinylene groups and hydrogen peroxide whose direct decomposition or subsequent photolysis will generate hydroxyl radicals. It is found that this reaction is quenched very efficiently by small amounts of HALS (Hindered Amine Light Stabilizers) and by amines in general. It is postulated that quenching is due to energy transfer from the charge‐tranfer complex polymer‐oxygen to a charge‐transfer complex HALS‐oxygen or amine‐oxygen. The data available so far suppo

ISSN:0258-0322    

DOI:10.1002/masy.19890270104

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe mechanism of the photo‐oxidation of an ethylene‐propylene random copolymer (EPM) has been compared with that of a styrene‐butadiene‐styrene block copolymer (SBS). The former is considered as a model for polyolefins that undergo chain scission on irradiation and the latter as a model for unsaturated rubbers that become cross‐linked. A hindered amine light stabilizer (HALS) that is a better inhibitor of the absorption of oxygen in SBS than in EPM is, however, less efficient to prevent formation of carbonyl groups and change of the mechanical properties. These results are discussed and an explanation is

ISSN:0258-0322    

DOI:10.1002/masy.19890270105

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractLuminescent species observed in the polyolefins were mainly foreign impurities, i.e., polynuclear aromatics (PNA) adsorbed from an ambient atmosphere. The luminescent species adsorbed under normal atmospheric conditions and an equivalent amount of PNA did not affect the photodegradation of high‐density polyethylene (HDPE). On the other hand, the extracted precipitates from HDPE accelerated the photodegradation of the polymer and, also, 3‐octanone slightly accelerated it, but little effect was observed in 1‐icosene. Therefore, the activity of impurities on the photodegradation of HDPE can be expressed in the following order:Extracted precipitates>>C=sO>PNA ∞

ISSN:0258-0322    

DOI:10.1002/masy.19890270106

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractA polymeric substance consists of long chainlike molecules forming complex non‐uniform structures. Both anisotropy of macromolecules and irregularity of their packing result in a marked deviation of polymer oxidation process from that of low‐molecular compou

ISSN:0258-0322    

DOI:10.1002/masy.19890270107

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe oxidation of a hydrogenated butadiene‐acrylonitrile (2:1 mole ratio) rubber has been examined by infrared (IR) spectroscopy and the use of γ‐initiation to give a controlled initiation step. The resolution and sensitivity of the IR technique was enhanced by the use of chemical derivatization in which carboxylic acids were measured as acid fluorides, hydroperoxides as nitrates and alcohols as nitrites. In all of these compounds, their spectra are sensitive to the precise substituents (primary, secondary or tertiary). Oxidation produced hydroperoxides from both tert. H‐C‐C=N and sec. H‐C‐H groups (≈︁1:1.1 mole ratio) as well as chain‐end carboxylic acids [‐CH2‐C(=O)OH]. From a comparison with measurements of peroxyl radicals produced at low temperature, average kinetic chain lengths for the various oxidation products were estimated and compared with these from oth

ISSN:0258-0322    

DOI:10.1002/masy.19890270108

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe distribution of stress at macroscopic and molecular levels can dramatically affect mechanical properties. This paper explores both these aspects. In the first part, quenching operations for polycarbonate and polystyrene were shown to develop favorable residual stresses as well as structural alterations (as manifested by changes in density, hardness, DSC results, etc.). The changes in these glassy polymers can be accompanied by as much as an order of magnitude increase in impact strength and fatigue life. In the other phase of our study, various analytical methods were used to investigate phenomena associated with fracture in oriented semi‐crystalline polymers. In the studies reported here, the combined effects of stress and environmental agents on mechanical strength of nylon, polyethylene, and Kevlar fibers were measured. These results, in conjunction with investigations of bond rupture kinetics, suggest that fracture in these materials involve thermally activated chain scission in which the activation energy is aided by stress and the chemical environment. Different mechanisms appear to dominate fracture in spherulitic forms of chemically similar polymer

ISSN:0258-0322    

DOI:10.1002/masy.19890270109

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe solubility of additives in polymers is shown to determine the state of the additive in a processed sample and the mechanisms by which it may be lost. The loss of additives is described in terms of a model which considers the effects of solubility, diffusion rate and volatility, and it is shown that the rate and mechanism of loss depends upon these quantities and upon the sample geometry. The effects of additive structure on loss mechanism and rate are discussed and the implications for additive design are reviewed.

ISSN:0258-0322    

DOI:10.1002/masy.19890270110

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractMolecular dynamics in crystallites of a number of polymers, such as polyethylene, nylon‐6, poly‐(vinyl alcohol), was studied at temperatures ranging from 4.2 to 400 K using the X‐ray diffraction technique. Thermal expansion of the lattice was measured by the temperature‐induced displacements of diffraction maxima. The thermal expansion coefficient was found to grow from 0 to ∼10−4K−1, this fact being the evidence of the quantum statistics in the vibrational dynamics of straightened molecules over the whole temperature range. Characteristic temperatures of vibrations were estimated. The kinetics of fracture was studied using highly ‐ oriented nylon‐6 and KEVLAR‐49 fibers. Tensile strength (σr) was measured as a function of loading rate σ and temperature (T) in the range from 4.2 to 400–600 K. The observed specific features of the σr(σ) and σr(T) curves at low temperatures correspond to tunnel scission o

ISSN:0258-0322    

DOI:10.1002/masy.19890270111

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractBoric acid esters and arylboronic esters and amides are known to be good primary antioxidants, but they are also capable of destroying hydroperoxides effectively. We have found three principal ways of hydroperoxide decomposition. At first, simple alkyl, but also other esters catalytically destroy hydroperoxides, e. g. cumyl and tert‐butyl hydroperoxide, after an induction period. In a second route, reduction of the hydroperoxides takes place under transformation of oxidizable parts of the organoboron compound. Boric acid catechol esters, for example, reduce tert‐butyl hydroperoxide giving a black precipitate, a reaction product of the instable o‐benzoquinone. Catechol and hydroperoxide in the absence of boron compound do not react. Finally, p‐phenylboronic acid esters reduce hydroperoxides to give alcohol and the corresponding boric acid ester. Many boron derivatives can react in two or all three ways, e. g. 2‐phenyl‐1, 3, 2‐benzodioxaborole. 1 mol of this compound destroys 2 mol of cumyl hydroperoxide giving cumyl alcohol, and more than 10 mol to give acetone and phenol. In side reactions, cumyl hydroperoxide is converted into dicumyl peroxide and acetophenone. The last compound indicates a reaction passing via radicals; but in all cases, this reaction is

ISSN:0258-0322    

DOI:10.1002/masy.19890270112

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY