Problems of Weight Gain and Filler Surface Treatment that Need to be Broken through in Plastic Modification Technology
Plastic modification technology has achieved certain achievements in academics, technology and industrialization, but there are still some recognized problems, which restrict the popularization of plastic modification technology and make it difficult to achieve greater social and economic benefits.
01. The “weight gain” problem
The density of non-metallic minerals is much larger than that of synthetic resins, usually two or three times larger, and some, such as barite powder, are about five times larger than that of polyethylene or polypropylene. The density of some mineral fillers does not seem to be too large on the surface, but it can only be said that the bulk density is not large. When it is really dispersed into the plastic matrix as a single particle, its true density is revealed. Although the mineral filler replaces the base plastic on a one-to-one basis by mass, it occupies only a fraction of the volume of the base plastic of the same mass.
If the particles of the mineral filler are in close contact with the matrix resin without voids, then this difference in volume will directly affect the quantity of plastic materials and articles measured by area or length, such as the length of pipes and profiles or the area of artificial leather; also directly affects the number of injection molded products. Because the volume of the mold cavity for injection molding is fixed, if the melt of the same quality has different volumes, the number of injection products that can be molded will be reduced. As a result, while the use of fillers reduces the cost of products and increases economic benefits, there are Negative effects of reduction in length, area, and number of products.
Plastic processors will weigh the effects of both positive and negative factors to determine whether fillers are necessary. It should be pointed out that some plastic products are not sensitive to the negative effects of weight gain caused by fillers, and even need to increase the density of plastic materials, such as plastic net sinkers for marine aquaculture, speaker shells (high quality and good sound effect) and some Appliance bases, etc. There are also some cases where the length or area of the product is not sensitive to the density of the filler, that is, in the final plastic material and product, the length and area obtained by the same quality of material do not change much, such as uniaxially stretched polypropylene flat yarn, Packing tape, tear film and polyethylene blown film, hollow container, etc.
This is mainly because during the processing of these plastic products, the matrix plastic is stretched or blown, and voids appear between the molecules, as well as between the macromolecules and the filler particles, so that the density of the filler material does not increase much, and more importantly It is the performance of this filling system that can still meet the requirements of use, which highlights the advantage of using fillers to reduce costs.
02. Filler surface treatment problem
Inorganic powder materials are used as fillers for plastics. In most cases, the surface of the particles should be organically converted, that is, from hydrophilicity to lipophilicity, which is usually called “activation”. Since the 1980s, coupling agents such as stearic acid, titanate, aluminate, phosphate, and silane coupling agents have been widely used as surface treatment agents for inorganic powder materials, and have achieved significant results.
However, with the in-depth research work of some experts and scholars and new theories or approaches, people realized that the surface treatment technology of filler particles and the effect of treatment are far from clear. Professor Yu Jian from Tsinghua University proposed the basic methods and principles to divide various microphase interfaces in polymer/inorganic powder composite systems by using the interaction between the constituent substances in the material system. Efficient methods to design and tune, resulting in a leap in the impact resistance properties of CaCO3/HDPE or CaCO3/PP systems.
Professor Zhang Wengong of Fujian Normal University put forward the principle, implementation steps and research of in-situ combined chemical modification of inorganic powder surface (referred to as CCM/NPS-IS) on the basis of years of exploration and summarization of the theory and practice of inorganic powder modification at home and abroad. The object and main content, etc., it is considered that this is the third generation of inorganic powder surface modification technology after coupling agent modification.
The scientific and technical personnel of Shanghai Zhehua Chemical Materials Co., Ltd., Shanghai Xinxing New Materials Co., Ltd. and Baoji Yunpeng Plastic Technology Co., Ltd. also made an impact on the principle and technology of inorganic powder surface treatment, and achieved encouraging achievements. These new ideas and methods are challenging the traditional surface treatment technology with coupling agent as the core, and the academic and technology of powder surface treatment is facing a major breakthrough.