Application of Compatibilizer in the Four Plastic Recycling Systems

As daily consumables, plastic products have become a large part of resource waste. For instance, beverage bottles are currently a major category of material recycling. However, the body and cap of beverage bottles are generally composed of different materials, for example, the bottle body is made of PET material while the bottle cap is made of PE material, but PET and PE are not compatible, which brings difficulties to the recycling end.

Most plastic products have problems that are difficult to handle, and the research and application of compatibilizers in recycling and modification can effectively cope with these problems. The use of compatibilizers to realize the blending and regeneration of waste plastics and turning them into new plastic alloys or new modified plastics is an effective way to solve the "white pollution" problem, reduce economic costs, and improve social benefits.

Generally speaking, the compatibilizer is used to blend different kinds of plastics together. This kind of additive can have good compatibility with two kinds of raw materials.

a. Non-reactive solubilizer

Non-reactive compatibilizers are currently more common compatibilizers. The method of realizing compatibilization by adding a non-reactive compatibilizer in an incompatible polymer system is common in polymer alloy technology. Non-reactive compatibilizers are generally copolymers, block copolymers, graft copolymers or random copolymers.

b.Reactive compatibilizer

The reactive compatibilizer is a random polymer composed of the non-polar polymer backbone and active groups such as hydroxyl and epoxy groups.

Generally, we take the recycled plastic as the base resin, and the copolymer obtained by grafting strong polar groups is used as the compatibilizer. The graftable groups include MAH, acrylic acid, butyl acrylate, methyl methacrylate (MMA), glycidyl methacrylate (GMA) and so on. The most common grafting monomer is MAH.

The body and cap of a beverage bottle are generally composed of different materials. For example, the bottle body is made of PET material, and the bottle cap is made of PE material. During recycling, common compatibilizers in PET/PE systems include various grafts, such as maleic anhydride (MAH) and glycidyl methacrylate (GMA).

Polycarbonate (PC) is a kind of thermoplastic engineering plastic with large demand, wide application and superior comprehensive performance. It is often blended and modified with ABS to reduce melt viscosity, improve processing performance, reduce internal stress of products, and prepare with high-strength resistance. Blended materials with impact, stretch and heat resistance are widely used in the automotive industry, electronic appliances, machinery, computers, medical care and other fields. Research on recycling waste PC and waste ABS material has good economic benefits and important significance for sustainable development. Optional compatibilizer components include styrene/maleic anhydride random copolymer, styrene/acrylonitrile/maleic anhydride terpolymer, ABS grafted maleic anhydride and so on. The materials with better comprehensive performance can be prepared by blending, which can be popularized and used in the fields of household appliances, mobile phones, auto parts and so on.

Paper/plastic/aluminum composite flexible packaging material is a common flexible packaging material. It is often used to make flexible packaging boxes for various beverages. It is composed of paper, plastic and aluminum foil. Generally, it has a 6-layer structure: polyethylene (PE)/paper layer/PE /Aluminum foil/Adhesive (AD)/PE; among them, the content of wood fiber (paper), plastic (PE) and aluminum are about 75%, 20% and 5% respectively. These three components are all recyclable resource.

The main component of wood fiber is cellulose, which contains a large number of functional groups such as polar hydroxyl and phenolic hydroxyl, so it is polar, while PE is non-polar, and the interface compatibility between the two is poor, and the presence of aluminum foil also increases the interface Complexity. In order to obtain composite materials with good performance, it is necessary to solve the problems of interfacial compatibility and interfacial bonding between wood fiber, aluminum foil and plastic.

Studies have shown that maleic anhydride grafted polyethylene (PE-g-MAH) can effectively improve the interface compatibility of the composite system, and the final mixed system with the increase of the amount of PE-g-MAH, the composite material Tensile strength and flexural strength increase first and then decrease, impact strength gradually increases, and water absorption first increases and then decreases. This is not only because PE-g-MAH can increase the compatibility of wood fiber with the plastic matrix and enhance the interface bonding effect, but also related to the degree of PE-g-MAH coating on the surface of wood fiber and its own strength.

Wood-plastic composites are based on wood fiber as the main raw material. After proper treatment, they can be combined with various plastics to produce high-performance, high-value-added new composite materials through different composite methods. As a new type of composite material, wood plastic not only has the properties of plastic and wood, but also is environmentally friendly and saves resources. It is a new method for processing waste plastics. However, the wood fiber is very polar while the waste plastic has almost no polarity (such as PE, PP, etc.), the bonding ability between the two phases is poor, and the performance is also reduced. Adding an appropriate amount of compatibilizer to surface treatment of waste plastics can improve the bonding condition.

The emergence of compatibilizers provides the possibility for polymer material alloys. Polymer alloys are multi-phase multi-phase alloys obtained by blending two or more polymer materials with different properties and adopting corresponding compatibilization technology. Component system. The important key material for such polymer alloys, blending, and modification is the compatibilizer. The compatibilizer plays a very good role in adjusting and controlling the microscopic phase structure of the alloy technology, and enables the blended material to achieve high performance and functional effects. Compatibilizers are widely used in PP/PE, PP/PA, PA/PS, PA/ABS, ABS/PC, PBT/PA, PET/PA, PP/POE, TPE/PU and other alloy systems.

Compatibilizers can also be called macromolecular coupling agents. The macromolecule part is compatible with the macromolecule polymer. Therefore, the compatibilizer has excellent coupling efficiency between the polymer and the filler. It can be used for PE/CaCO₃, PE/talc, PA/GF, PRT/GT, etc. Joint processing.

When the compatibilizer is incorporated into the non-polar and polar polymers with active free radical molecules, the carboxyl group acts as a "bridge", and it is modified into a polar modified polymer, and then it is combined with the polar polymer. Blending, the reaction between the two to obtain a good modified blending effect. For example, the compatibilizer provides the most critical "core" and "shell" compatibility of the toughener. Adding a certain amount of the compatibilizer can be used as a toughening agent for PP, PE, PS, PA, PC and other plastics.

The compatibilizer can recycle two or more different types of old plastics with different properties into new materials, thereby reducing resource waste, and the new system obtained often has better performance.

Therefore, compatibilizers play a key role in the recovery of waste plastics and the modification of original resins. Research on this will be further carried out with the requirements of resource recovery.