Plastic modification and recycling

The development of plastic modification technology not only greatly improves the performance of materials, but also gives new properties, further expands its application fields, and significantly improves the industrial application value of plastics, and has a very important position in production practice. At present, the commonly used plastic modification methods include blending modification technology, filling modification and fiber reinforcement technology, chemical modification technology and surface modification technology. The development status of these plastic modification technologies is simplified. Introduction.

1 Introduction

With the development of science and technology, synthetic materials have been widely used, and have penetrated into various fields of human production and life. Together with steel, cement and wood, they have become the four basic materials of modern industry and occupy an important position in the national economy. The rapid development of the plastics industry brings two real and important issues: the recycling of waste plastics and the modification of plastics.

By the year 2000, the total output of plastics in the world has exceeded 110 million tons, and the annual growth rate of about 8% has continued to increase. Since the reform and opening up, the consumption of plastics in China has maintained a double-digit growth rate. It reached 21,985,500 tons [1]. The wide application of plastic products has facilitated people's production and life, and also brought about the "white pollution" problem that has attracted the attention of the whole society.

The wide application of plastics puts forward higher requirements on material properties. Single polymer materials can no longer meet the needs of production and life, and materials must be modified. The so-called plastic modification refers to the physical, chemical or physical/chemical methods to meet the production and living needs of the plastics, or to reduce the production cost, or to improve the performance of the material, or to be given a new function [2] ].

2. Overview of research on plastic modification

There are many modification methods for plastics, which can be divided into blend modification, filling and fiber reinforcement modification, chemical modification and surface modification [3].

2.1 Blending modification

Blending modification is the simplest and straightforward method for plastic modification. It mainly refers to the process of adding one or more other polymers or modifiers to the matrix polymer to prepare macroscopically uniform materials, usually including physics. Blending, chemical blending and physical/chemical blending. In a sense, the chemical structure of the polymer macromolecular chain did not change drastically, mainly due to changes in system composition and microstructure.

The blending of plastics with different properties can greatly improve the performance of the polymer. The toughening modification of plastics is widely used in production practice and is one of the most successful examples in blending modification. Wu Chifei et al [4-6] used recycled PET flakes as the main raw material, and borrowed the advantages of low temperature solid phase processing and reactive extrusion. The co-directional twin-screw extruder was used to blend PET/PC/SEBS system. Using 4,4'-diphenylmethane diisocyanate (MDI) as chain extender for chain extension and compatibilization, a new type of beam with a notched impact strength of >65kJ/m2 and good strength and toughness was prepared. Polymer alloy. Guimariäes et al. [7] studied the mechanical properties and thermal properties of HDPE/POE blends. The results showed that HDPE and POE had some interaction, and the tensile properties of the blends were significantly improved. When the POE dosage reached 5 wt%. , room temperature super tough material can be obtained. Feng et al. [8] studied the phase structure and toughening mechanism of PP/POE blends. The results show that POE forms a uniform Salami structure in PP, which can effectively improve the normal temperature and low temperature impact strength of PP.

The blending technology can not only use the complementary performance of different plastics to prepare new polymer materials with excellent performance, but also can realize the blending of expensive plastics with relatively inexpensive plastics without reducing or slightly reducing the performance of the former. Lower production costs.

2.2 Filling and fiber reinforced modification

In the process of polymer processing, in order to improve the performance of a certain plastic or reduce the production cost, in many cases, different proportions of fillers are added to the plastic, and most of these fillers are inorganic powders or fibers. Among the filler-modified systems, a more successful example is the application of nano-calcium carbonate and montmorillonite in plastics.

Hu Shengfei et al [9] research on PVC/CaCO3 system and PVC/ACR/CaCO3 system showed that when the amount of nano-CaCO3 is 10wt%, the tensile strength of the material reaches the maximum, which is more than the corresponding PVC and PVC/ACR blend. The tensile strength of the material is high; at the same time, the impact strength of the material is also significantly improved. Ren Xiancheng [10] and other studies on the nano-CaCO3 toughening and strengthening PP system found that when a small amount of CaCO3 was added, it mainly played a reinforcing role. As the amount of CaCO3 increased, the volume fraction of the flexible interfacial layer inside the composite increased. The flexible interface layer yields under the external force before the matrix, resulting in a decrease in the tensile strength of the material.

Fiber reinforced composite materials have the characteristics of “light weight and high strength” and are a class of outstanding materials, which are widely used in national production. Commonly used fiber types are glass fiber, carbon fiber, aramid fiber, etc. The thermoplastic matrix has PP, PA, PBT, PC, ABS, POM, PPS and P.

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