Polyvinyl chloride (PVC) is one of the five general-purpose plastics, and its products have a wide range of uses. However, PVC has the disadvantage of poor thermal stability, and it is necessary to add a suitable heat stabilizer during processing to suppress thermal degradation. Regarding the types and functions of additives in PVC ingredients, we have also introduced them before, and interested friends can check out our previous articles. Today we are going to introduce β-diketone compounds such as dibenzoylmethane (HDBM).

Β-diketone compounds such as dibenzoylmethane are very effective in improving the initial coloring ability of zinc-based heat stabilizers to inhibit PVC and greatly improve their thermal stability. They have become a key group of high-performance zinc-based non-toxic heat stabilizers. Minute. However, the presence of β-diketone has the disadvantage of redness of filled PVC products, which severely limits the application range of β-diketones and also affects the promotion of environmentally friendly zinc-based heat stabilizers. The reasons and solutions to this problem were discussed.

Β-diketone compounds such as dibenzoylmethane (HDBM) are a class of oxygen-containing complexing agents having a conjugated structure, which are effective for absorbing ultraviolet rays and forming stable metal complexes, usually in the formation of metal complexes. The absorption spectrum is red-shifted and the absorption intensity is increased. Therefore, the β-diketone compound is significantly darkened in the formation of the metal complex. According to this characteristic of the β-diketone compound, and considering the fact that the unfilled PVC product containing β-diketone does not have redness, it is speculated that the β-diketone-filled PVC will be reddish. The reason should be that some or some metal ions are present in the filler, or they can form a red complex with the β-diketone compound. According to the chemical industry standard HG222691, in the industrial light calcium, in addition to the main component containing CaCO3, the main impurity is Fe, and its mass fraction may be as high as 1×103. Since the Ca2+ complex of β-diketone is yellow rather than red, it can be judged that the red metal ion of the light calcium-filled PvC product containing β-diketone should be the impurity Fe3+. Experiments have shown that Fe3+ does form a deep red color with β-diketone.

Further experiments to form Fe3+ complexes are the reason for the redness of filled PVC products containing β-diketones. The redness of PVC filled with β-diketone (hereinafter referred to as heavy calcium) is lighter than that of light calcium filled PVC. The filled PVC containing stearyl benzoylmethane (HDBM) is lighter than those containing HDBM. The reason for the former may be that the heavy calcium is directly pulverized by natural ore, and the natural ore structure is stable, in which Fe does not easily diffuse to the surface of the granule and reacts with β-diketone, and the latter should be stearyl succinyl methane iron complex [Fe(SBMy)] is a lighter color.

in conclusion

1) The reason why the β-diketone-filled PVC plastic is red is that the filler contains Fe3+, and Fe3+ can form a red match with the β-diketone.

Compound.

2) By performing a special chemical modification treatment on β-diketone, the redness of PVC filled can be effectively alleviated.