1. "polyethylene (PE) blending modification"
Polyethylene (PE) resin is formed by monomer ethylene polymerization. Due to different polymerization reaction conditions such as pressure and temperature during polymerization, different densities of resin can be obtained. Therefore, it is divided into high density polyethylene, medium density polyethylene and low density polyethylene.
Low density polyethylene (LDPE) is a white waxy granular solid with a density of 0.91~0.925g/ cm3. LDPE is typical of crystalline polymer, crystallinity was 55% ~ 65%, melting point is 105 ~ 126 ℃ : LDPE is polar materials, easy with static electricity.
Medium density polyethylene (MDPE) is a polyethylene with a density of 0.926 ~ 0.94g/ cm3, having the same performance as LDPE. Due to the increase in density, the crystallinity of MDPE is up to 70% ~ 80%.
High density polyethylene (density 0.94~0.965g/ cm3) has better rigidity, strong toughness, mechanical strength, solvent resistance and stress cracking resistance than LDPE.
2. What is blending modification?
The modification can be divided into chemical modification and physical modification, and the blending modification of PE is physical modification. HDPE plastic has great hardness and lacks flexibility. LDPE plastic is soft, but has poor strength and air tightness. A series of blends with intermediate properties can be obtained from two polyethylene blends with different densities. Increased rigidity and strength can cut the thickness of some plastics in half, thus reducing costs.
The blending modification of polyethylene is one of the most commonly used technologies in the factory. Through the piecemeal application of the blending modification technology of polyethylene, it can basically meet the different requirements of polyethylene products. Polyethylene produced by different blends and manufacturers is blended in proportion to improve the molecular weight distribution of materials and the distribution of micro additive elements in materials. It is often used for extrusion blow molding PE easy to receive better results. Starting from the chemical performance, mechanical performance and various technological properties in production, we can freely design different formulas to meet various requirements, and often achieve the purpose of reducing production cost.
3.Experiment and result of blending modification
Yin jinjie and wang yapeng from the department of materials of liaoning university of engineering and technology carried out a study on the effect of HDPE on the performance of LDPE/HDPE blend, and tested the properties of tensile strength and impact strength by blending extrusion, granulation and other processes.
The results showed that HDPE content in LDPE/HDPE blend had the greatest influence on tensile strength of the blend. The results showed that the maximum tensile strength was 25.7mpa when the content of HDPE was 30%. When the content of HDPE was 40%, the samples had the best toughness, i.e. the maximum breaking elongation, which was 777%.
4.The role of blending modified plastics in recycling waste plastics
In the recycled waste plastics, it is difficult to process the mixed recycling due to the differences in the properties of various plastics. After the second melt, the molecular structure chain is shortened, the strength and tensile strength and other properties will be reduced, and the quality and quantity index of the plastic products produced will fall down, which is not enough to make use of, and the cost is high, the added value is low, the profit is low. However, if different plastics are mixed and modified according to the demand, different properties of plastics will be obtained, with different use values. The secondary melting of plastics has been widely used.