Exposure to ultraviolet (UV) radiation may cause the significant degradation of many materials. UV radiation causes photooxidative degradation which results in breaking of the polymer chains, produces free radical and reduces the molecular weight, causing deterioration of mechanical properties and leading to useless materials, after an unpredictable time. Polystyrene (PS), one of the most important material in the modern plastic industry, has been used all over the world, due to its excellent physical properties and low-cost. When polystyrene is subjected to UV irradiation in the presence of air, it undergoes a rapid yellowing and a gradual embrittlement. The mechanism of PS photolysis in the solid state (film) depends on the mobility of free radicals in the polymer matrix and their bimolecular recombination. Free hydrogen radicals diffuse very easily through the polymer matrix and combine in pairs or abstract hydrogen atoms from polymer molecule. Phenyl radical has limited mobility. They may abstract hydrogen from the near surrounding or combine with a polymer radical or with hydrogen radicals. Almost all synthetic polymers require stabilization against adverse environmental effects. It is necessary to find a means to reduce or prevent damage induced by environmental components such as heat, light or oxygen. The photostabilization of polymers may be achieved in many ways. The following stabilizing systems have been developed, which depend on the action of stabilizer: (1) light screeners, (2) UV absorbers, (3) excited-state quenchers, (4) peroxide decomposers, and (5) free radical scavengers; of these, it is generally believed that excited-state quenchers, peroxide decomposers, and free radical scavengers are the most effective. Research into degradation and ageing of polymers is extremely intensive and new materials are being synthesized with a pre-programmed lifetime. New stabilizers are becoming commercially available although their modes of action are sometimes not thoroughly elucidated. They target the many possible ways of polymer degradation: thermolysis, thermooxidation, photolysis, photooxidation, radiolysis etc. With the goal to increase lifetime of a particular polymeric material, two aspects of degradation are of particular importance: Storage conditions, and Addition of appropriate stabilizers. A profound knowledge of degradation mechanisms is needed to achieve the goal.

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Photodegradation and photostabilization of polymers, especially polystyrene: review

An investigation of chemical crosslinking effect on properties of high-density polyethylene

The DC conductivity of polymer blends composed of poly(ethylene-co-vinyl acetate) (EVA) and high density polyethylene (HDPE), where a conductive carbon black (CB) had been preferentially blended into the HDPE, were investigated to establish the percolation characteristics. The blends exhibited reduced percolation thresholds and enhanced conductivities above that of the individually carbon filled HDPE and EVA. The percolation threshold of the EVA/HDPE/CB composites was between 3.6 and 4.2 wt % carbon black, where the volume resistivity changed by 8 orders of magnitude. This threshold is at a significantly lower carbon content than the individually filled HDPE or EVA. At a carbon black loading of 4.8 wt %, the EVA/HDPE/CB composite exhibits a volume resistivity which is approximately 14 and 11 orders of magnitude lower than the HDPE/CB and EVA/CB systems, respectively, at the same level of incorporated carbon black. The dielectric response of the ternary composites, at a temperature of 23°C and frequency of 1 kHz, exhibited an abrupt increase of ca. 252% at a carbon concentration of 4.8 wt %, suggesting that the percolation threshold is somewhat higher than the range predicted from DC conductivity measurements. Percolating composites with increasing levels of carbon black exhibit significantly greater relative permittivity and dielectric loss factors, with the composite containing 6 wt % of carbon black having a value of ∈' 79 and ∈ 14.

Reduced percolation thresholds of immiscible conductive blends

https://www.fpl.fs.fed.us/documnts/pdf2015/fpl_2015_wei001.pdf

Grafting of bacterial polyhydroxybutyrate (PHB) onto cellulose via in situ reactive extrusion with dicumyl peroxide.

Thermally recyclable polylactic acid/cellulose nanocrystal films through reactive extrusion process

Polyethylene containing large quantities of carbon black can be crosslinked by a chemical free radical mechanism utilizing the thermal decomposition of dicumyl peroxide as the source of free radicals. Crosslinking in the presence of different types of blacks was studied in a liquid paraffin model system. The information obtained from this study provides a logical basis for speculation on the mechanism of crosslinking of carbon-black-loaded polyethylene compositions. Evidence is presented that the grade of carbon black is an important factor and that the course of the peroxide decomposition is largely determined by the chemical nature of the carbon surface. Carbon blacks having a highly oxygenated surface cause an ionic decomposition which is not effective for crosslinking, while those of low oxygen content allow the decomposition to follow a free radical mechanism which results in the crosslinking of polyethylene. Marked changes in the physical characteristics of the polymer are brought about as a result of pigmentation and subsequent crosslinking. Such compositions display a surprising degree of flexibility and strength over a wide range of temperatures. Moreover, significant strength is observed at temperatures above the crystalline melting point of the polymer. These improved properties are attributed to the reinforcing ability of the carbon black and the crosslinked network of polymer chains.

Peroxide crosslinked carbon black polyethylene compositions

A comprehensive study of the performance of various types of carbon black in polyethylene has been made. The physical and chemical properties of carbon blacks are discussed, and the effectiveness of various blacks as ultraviolet screening agents for polyethylene is assessed. It is seen as a first approximation that primary particle size is the property of the carbon black which largely governs the weatherability of a compound. The data suggest that this is due to that fact that the degree of ultraviolet protection is dependent on the presence of submicroscopic aggregates and their distribution throughout the polymer mass. It is proposed that the aggregate size and distribution are largely controlled by the surface energy arising from the dimensions of the primary particles. Studies of carbon black-antioxidant systems gave results which were in agreement with those of Hawkins et al., who found that carbon blacks having a polar surface exhibit a synergistic behavior with organosulfur type antioxidant, greatly increasing the time required to absorb a given amount of oxygen or undergo thermal degradation. The present study shows that use of antioxidants also contributes to the ability of polyethylene compounds to resist accelerated aging. Outdoor aging of the same compounds are in progress, but more time is required to see if antioxidants are helpful in the manner indicated by the accelerated weathering studies. The effect of carbon blacks on the mechanical properties of polyethylene is discussed, and data are presented to show that higher loadings of carbon black than normally used for ultraviolet protection greatly increase the tensile yield (stress at draw point) at relatively fast rates of applied stress. It is suggested that the use of moderately high concentrations of carbon black would enhance the performance of polyethylene in applications such as pipe which often fails under rapidly applied stress.

Effect of the chemical and physical properties of carbon black on its performance in polyethylene

A PROCESS IS DESCRIBED FOR MAKING A FURNACE CARBON BLACK WHICH IS WELL SUITED FOR USE AS A REINFORCING FILLER IN RELATIVELY SATURATED SYNTHETIC ELASTOMERS. THIS PROCESS INVOLVES CONVERTING A HYDROCARBON RAW MATERIAL TO CARBON BLACK IN A FURNACE OPERATED SO AS TO PRODUCE A BLACK OF RELATIVELY LOW STRUCTURE AS INDICATED BY AN OIL ABSORPTION VALUE BELOW ABOUT 155 POUNDS OIL PER 100 POUNDS OF BLACK. THE RESULTANT BLACK IS THEN TREATED WITH A CHEMICAL OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OF NITRIC ACID, NITROGEN OXIDES, OZONE AND MIXTURES THEREOF UNTIL THE PH OF SAID BLACK HAS BEEN REDUCED TO ABOUT 4 OR BELOW, THE VOLATILE CONTENT HAS BEEN INCREASED TO ABOUT 3% BY WEIGHT OR MORE AND THE DIPHENYL QUANIDINE UPTAKE FOR A HALF GRAM SAMPLE OF SAID BLACK HAS BEEN RAISED ABOVE ABOUT 25%.

Process for treating furnace carbon black

Disclosed herein are carbon black-containing asphalt compositions having improved properties of resistance to thermal and actinic oxidation.

Dannenberg Eli M

Papers

Peroxide crosslinked carbon black polyethylene compositions

Effect of the chemical and physical properties of carbon black on its performance in polyethylene

Process for treating furnace carbon black

Oxidation resistant asphalt compositions

Pigmented compositions and method of manufacture