Can we use MDH in silicone rubber?-1

Hello Everyone, how are your doing? Sorry for the delays on this month’s update. That is because I went to #Chinaplas 2021 this month, it was my first time to participated in such a grand exhibition. I met a lot of people and I learned a lot from them at the exhibition.

As we all know that MDH could be used in many industries, such as building material, cable and wire, water treatment, etc., and there are still many market needs to explore. During 4 days exhibition, there are many exhibitors asked me if they can use MDH in their silicone rubber. Well, I have been focused on the application of MDH in cable industry since I came to KMT industrial, so instead of give them answer right away, I asked our technical for help. And he told me that MDH could be used in silicone rubber. And he also shared a paper titled “Preparation and properties of magnesium hydroxide flame retardant silicone rubber”. So this passage is to summarize what I have learned from this paper to you.

1. Introduction

Silicone rubber has excellent properties such as high and low temperature resistance, weather resistance, and ozone resistance, and is widely used in various fields. However, silicone rubber itself is flammable and will continue to burn when exposed to fire, which limits its applications in electronic and electrical, wire and cable, automotive, aerospace and other fields. Therefore, flame retardant modification of silicone rubber is needed to expand its application.

Compared with halogen flame retardants and phosphorus flame retardants such as red phosphorus and phosphate esters. Halogen-free flame retardant magnesium hydroxide and aluminum hydroxide are getting more attention due to them have no harmful gases are released during combustion, and the residue after combustion will not pollute the environment.

However, magnesium hydroxide and aluminum hydroxide have obvious flame retardant effects only when they are added in a large amount, and a large amount of magnesium hydroxide will cause a great influence on the mechanical and electrical properties of silicone rubber. To solve this issue, we need to do surface modification to magnesium hydroxide, which will help increase its dispersion in silicone rubber and improve its interface compatibility with silicone rubber, so that silicone rubber can achieve better flame retardant performance while maintaining good mechanical properties.

This experiment studied the effects of magnesium hydroxide on the flame retardant, mechanical and electrical properties of silicone rubber after being treated with different surface modification agents.

2. Experiment

In this experiment, the raw material including silicone rubber, non-coated magnesium hydroxide, stearic acid treated MDH and silicone treated MDH, fumed silica etc.

Mix the silicone rubber A and silicone rubber B in an open mill, then add fumed silica and hydroxy silicone oil, mix them evenly, and then make them into pieces, and heat them in a 150℃ oven for 2 hours. After standing for 12 hours, add magnesium hydroxide and vulcanizing agent DBPMH on the open mill, mixing evenly and get plate. Then using plate vulcanizing machine to vulcanize under 165℃, the vulcanization time is determined by the positive vulcanization time (T 90): The secondary vulcanization is carried out in the oven under 200℃x4h.

Then a series of tests are conducted on the sample, to test the tensile strength, elongation at break, combustion test, oxygen index,etc...

Figure 1 Effect of the type and dosage of MDH on the limiting oxygen index of silicone rubber

From figure 1 we can see that along with the increase of MDH adding amount, the oxygen index is increasing. And also we can learn that silicone treated MDH can provide better flame retardant performance in silicone rubber.