The influence of the relative molecular weight of natural rubber on its thermo‐oxidative stability

synopsisEffectivenesses of 2,Mitertiarybutyl cathecol (Dnx), tri(mono-anddi-nonyl-phenyl mixture) phosphite (Plg), and their mixtures as antioxidants for CBR are determined. The activation energies of oxidative degredation for CBR are calculated. An attempt is made to corrolate the results obtained from experimental studies to storage time of CBR under ambient conditions. The relevant experiments are done mainly by differential scanning calorimetry. IR spectroscopy is used for effectiveness studies near room temperatures. Quantitative determinations of antioxidants in CBR samples are carried out by UV spectroscopy. It is found that, as a n antioxidant, Dnx is more effective than Plg. When their mixture is used, 60% addition of Plg to Dnx gives almost the same effectiveness. When 45% Plg is added, maximum effectiveness is achieved and Plg is synergist to Dnx. Activation energies calculated are in good agreement with the values given in the literature. To corrolate the retarded oxidation periods obtained from DSC studies to room temperatures, DSC studies at temperatures where relative effectivenesses of different antioxidants to each other do not change by temperature must be carried out.As in the case of other polymeric materials, CBR oxidizes by reacting with oxygen. Since oxidation affects the properties of CBR in an undesirable way, various antioxidants are used to retard or preferably inhibit its oxidation during production, storage, processing as well as usage under the application conditions. Nowadays, various antioxidants are produced which are mainly phenolic compounds, alkyl aryl phosphites, dithiocarbonate or thiozyl derivatives. Furthermore, their number on the market is continuously increasing. 2,3 Therefore, selection of the most suitable antioxidants

Section: Methodsmentioning

confidence: 99%

Determination of effectivenesses of 2,6‐ditertiarybutyl cathecol tri(mono‐and‐di‐nonyl‐phenyl mixtures) phosphite and their mixtures as antioxidants for CBR, by DSC

Savaşçı¹,

Baysal²

1986

Effect of resin components on the degradation of guayule rubber

Bhowmick

Rampalli

McIntyre

1985

SynopsisAll natural rubbers are likely to contain some long chain fatty acids or their esters. The individual effect of the four CIS fatty acids (stearic, oleic, linoleic, and linolenic acid) present in the guayule resin on the degradation of guayule rubber has been investigated concurrently by stress-relaxation of radiation cured rubber networks and by gel permeation chromatography studies on the raw rubber in the temperature zone 70-125°C. CIS unsaturated fatty acids enhance the degradation of rubber several fold. The rate of degradation follows the order: rubber < rubber + stearic acid < rubber + oleic acid < rubber + linoleic acid < rubber + linolenic acid. The thermal degradation is slower than the thermooxidative. The rate of degradation monotonically increased with the number of conjugated double bonds and is first order with respect to acid concentration. The activation energy for the chain scission for both thermal and thermooxidative degradation has been found to be 95 & 10 kJ/mol. The mechanism of degradation of guayule rubber in the presence of fatty acids is discussed.

Modification of atactic polypropylene to prepare emulsions by oxidation in melt

Yaykin

Savaşçi

Baysal

1989

SynopsisOxidation of atactic polypropylene (APP) obtained as by product from polypropylene production is studied in melt to obtain polymers which are easily emulsified by commercial emulsifiers. The experiments are done using a stirred, jacketed glass reactor and the relevant heating, air-feeding, and sampling attachments. Oxidation is followed by the change of carbonyl absorbance, iodine number, acid number, molecular weight, and melt flow index (MFI) by time. The relevant tests are done by infrared (IR) spectroscopy and gel permeation chromatography (GPC) and standard tests with minor modifications are applied. It is found that as temperature, air flow rate, and mixing speed are increased, higher oxidation rates are obtained. It is also found that initiator types and concentrations used are not as effective as the above parameters. By oxidation as molecular weight reduces, molecular weight distribution narrows. Correlation between MFI, iodine number, and molecular weight of the oxidized APP is also made for easy follow-up of oxidations. In addition, it is found that for easy and stable emulsions, APP must be modified by oxidation to iodine number and MFI higher than 30 mg/g and 3.5, respectively.