Application scope and purpose of PEG

PEG-4000 is usually used in rubber because if the molecular weight of polyethylene glycol is low, its compatibility with rubber is poor, and it is prone to precipitation, and it is inconvenient to add it in liquid form; When the molecular weight is too high, the alcohol groups per unit mass are relatively small (i.e., the hydroxyl value is low), and the effect of neutralizing acidity will be poorer.

Polyethylene glycol with a molecular weight of 4000 appears as a solid sheet, making it easy to process and add. It is not easily precipitated and belongs to the category of medium molecular weight polymers, with relatively better compatibility with rubber.

Polyethylene glycol PEG-4000 has multiple functions in rubber, as follows:

1. Processing aids

It can increase the extrusion speed of the rubber material, improve the demolding performance, make the surface of the product shiny, and help to remove moisture during vulcanization. When applied to tires and rubber molded products, PEG-4000 has a good lubricating effect, making the surface of the product smoother. In the production process of natural rubber and synthetic rubber, it can also serve as an internal release agent, which has the advantage of not evaporating, not producing ash, keeping the mold clean after demolding, and making the surface of the molded product smoother and cleaner.

2. Vulcanizing agent

The function of regulating the bonding performance between raw rubber and fillers (especially white fillers), as well as reducing the Mooney and increasing the vulcanization rate, has a good activation effect on thiazole accelerators, which can improve the vulcanization rate and crosslinking degree. This is particularly evident in the formula of extrusion microwave continuous vulcanization reinforced with EPDM white CB. However, for products bonded to metal, it is best not to use PEG.

3. Active agents for acidic fillers

Especially for white carbon black, PEG-4000 can be used as a treatment agent for white carbon black to activate the vulcanization system and wet the surface of acidic fillers such as white carbon black. There are two reactions involved here, one is a neutralization reaction, and the other is similar to a covering effect. Because acidic fillers can adsorb accelerators, it should be noted that their usage is directly proportional to factors such as the acidic surface area and dosage of the acidic fillers. Basically, it can be understood that the acidic surface has been neutralized. As for other acidic substances that appear in sulfurization reactions, such as HS, they are handed over to zinc oxide for treatment.

4. Activate dispersant

When used as an activating dispersant in rubber compounds with various fillers and pigments, it can reduce or eliminate the influence of fillers on vulcanization, promote the uniform dispersion of various additives, prolong the burning time, and improve the physical and mechanical properties of rubber products. Among various colored rubber products, it can make the color of the product more vibrant. Due to its polarity characteristics, it can also enhance the microwave absorption ability of non-polar rubber (such as EPDM). In addition, with the increase of molecular weight, the activity of PEG will decrease appropriately, and the modification effect on the hydroxyl groups on the surface of the filler will be slightly weakened. At the same time, the coke activation of the promoter will also be weakened. That is to say, with the increase of molecular weight, it helps to stabilize the vulcanization coke, but has a slightly adverse effect on the reinforcement of the material and rubber.