COMPARISON OF THREE DIFFERENT DEGRADATION METHODS TO PRODUCE LIQUID EPOXIDIZED NATURAL RUBBER

ABSTRACT Epoxidized natural rubber (ENR) has a high molecular weight, which has limited its solubility and processibility. For many potential applications, such as adhesives and coatings, ENR needs to be degraded into shorter chain lengths to form liquid ENR (LENR). We compared three different methods of preparing LENR: mechanical milling, chemical degradation initiated by potassium peroxodisulfate, and photooxidation initiated by ultraviolet (UV) irradiation. All the methods break down the ENR via free radicals but at different rates and by different mechanisms. In the LENR produced by these methods, ketone, aldehyde, carboxylic acid, and ester and lactone groups were observed; however, a hydrofuranic structure was only formed with UV degradation. The oxirane group was not affected significantly during the degradation, indicating that the chain sessions occurred predominantly via the –C=C– bonds. Spectroscopic analyses revealed that the consumption of a double bond is related to the extent of degradation initiated by potassium peroxodisulfate and UV irradiation. Mastication with a two roll mill produced LENR with a greater degree of unsaturation and fewer polar groups; therefore, presumably, significant chain scissions occurred from the rupturing of –C–C– single bonds. Comparing the reaction time, more LENR was obtained by UV degradation. As expected, an increase in the oxygen concentration led to the generation of more radicals, which could result in some coupling reactions.

Redox Power Changes of Caramels and Sugar Reductones in Beer

<p>Aerated or nitrogenated solutions of various sugars (10 % w/w) in deionized water, brewing water or phosphate buffers with dichlorophenolindophenol (DCIP) addition (10 mg/l) were heated 45 min at 60 °C and absorbance at 520 nm (?_max of DCIP at pH 4.6) and 610 nm (?_max of DCIP at pH &gt;6) was measured. Reduction power of the solutions increased with the absence of oxygen, increasing pH value and the kind of sugar (FRU&gt;LAC,MAL,GLU&gt;SUC). Aerated solutions of various sugars were also autoclaved (10 min at 121 °C) and the absorbance at 420 nm was measured. The color of caramels from sugars was dependent on the kind of sugar (FRU&gt; LAC,MAL,GLU&gt;SUC), and it increased with increasing pH value. The formation of caramel pigments from ascorbic acid or maltose by oxidation with potassium peroxodisulfate or hydrogen peroxide was also compared. The formation of colored pigments is considered to be the mark of irreversible aging of food.</p>