Discoloration problem of isoprene rubber
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Dear teachers: The color of isoprene rubber is powdery, dull, and uneven； If pressed for a long time, it will also turn darker or redder, with uneven coloring; I seek guidance! Thank you!
I suggest starting from the perspective of raw material ratios, carefully comparing the components of the formula, as well as considering temperature and reaction time
1. Are you referring to the raw rubber blocks? 2. What antioxidant is used? 3. Is cooling control available after shutdown? 4. Is residual monomer a monitoring indicator? Do the residual monomer levels change before and after color change of the same piece of adhesive?
Thank you! It refers to the off-line adhesive blocks; phenolic anti-aging agents are used in their formulation, and now there is a plan to switch to BHT ； After being taken off the line, the temperature of the glue block is around 60-70 degrees ； Residual monomers not measured!
This post was last edited by legendlcw on 2016-10-4 07:15. I’m thinking about the discoloration issue with other types of adhesives, and here are my current observations: 1. It’s important to choose the right type of antioxidant; BHT might be too inadequate for this purpose. A sufficient amount must also be added, as a large quantity of antioxidant is consumed during passage through the extruder; moreover, the antioxidant content decreases rapidly as the rubber mass cools down. 2. Both the off-line temperature and the cooling process of the gel block after it is taken off the line have a significant impact on degradation; the faster it is cooled, the less likely it is to change color. This is in accordance with the time-temperature equivalence principle. 3. Residual monomers need to be monitored repeatedly at the time of production completion, after storage for a period of time, and once discoloration occurs. What I observed was that the amount of residual monomers increased over time, indicating that degradation mainly involves the breakage of molecular chains. 4. I suspect that the color change is due to the formation of many tiny residual monomer bubbles within the gel mass, which causes light scattering and thus results in color. What color will it be exactly? My rubber variety produces colors ranging from yellow to brown, while isoprene gives colors from pink to red. I think this is related to the density and volume of the monomer bubbles, as they cause different types of light scattering.