An introduction to eco-friendly PLA coated paper

In order to improve the performance of paper, one layer or two layers of plastic films are often coated on the surface of paper to construct paper-plastic composite materials, known as coated paper. The film-coated paper is a composite material in which plastic particles are coated on the surface of paper by a extrusion casting machine. The superiority of film-coated paper includes oil-proof, water-proof and heat-sealable. The characteristics of the film-coated paper are depended on the application scenario. When the film-coated paper is used to package hamburgers, its oil-proof property comes into play. For instance, when it is used in McDonald's, the edible vegetable oil should not leak at 80℃ in 10min. And most commonly the film-coated paper is used to avoid water. Meanwhile, the heat-sealing property is significant in automatic packaging machine due to the high production speed.

Polylactic acid is also called polylactide (PLA). PLA is a polymer which is made from the polymerization of lactic acid. The raw materials of PLA are mainly corns and cassavas, which are abundant and renewable. The production process of PLA is pollution-free, and the product can be biodegradable, so it is an ideal green polymer material. PLA exhibits many excellent properties such as good thermal stability, solvent resistance, and can be processed in many ways. In addition to biodegradability, the products made of PLA are widely used due to  good biocompatibility, glossiness, transparency, hand feeling, heat resistance, as well as certain antibacterial, flame retardant and ultraviolet resistance.

PLA coated paper refers to the composite material coated on the surface of paper by the biodegradable material PLA instead of traditional polyethylene (PE), which has been widely used in the production of paper cups, paper bowls and paper bags. Compared with PE coated paper, PLA coated paper has two main advantages:

1. PLA is more environment–friendly than PE.

The raw materials of PLA are plant resources, which are renewable, and the production process of PLA is pollution-free. PLA is biodegradable, and the final degradation products are water and carbon dioxide, so it is an ideal green polymer material. However, the raw materials of PE generally come from fossil resources, which will consume non-renewable resources, and the PE products are difficult to degrade (more than 100 years). The discarded PE coated paper products will cause white pollution. Thus, the use of PLA for coating conforms to the global environmental protection policy of plastic restriction and plastic prohibition.

2. PLA is safer than PE.

PLA has good safety performance. PE coated paper may be oxidized to carbonyl compounds in the process of hot melting or smearing on cup paper, and the cup may emit unpleasant odor when poured into hot water. PLA coated paper has no peculiar smell, and has certain antibacterial and ultraviolet resistance.

In addition, PLA coated paper has good high/low temperature resistance, and it will not leak or deform when it is made into cold and hot liquid containers. Its coating layer is even and smooth, with good hand feeling, high adhesion and glossiness. Moreover, PLA coated paper has better characteristics of water resistance and oil resistance than traditional PE coated paper.

The properties of PLA coated paper produced by Hunan Green Star Biotechnology Co. Ltd is superior than that of many other companies. Generally, many problems exist in processing of PLA coated paper, such as frequently break during the production of paper cups or bags, the difficulty of coating with thin paper (<100g), and high cost due to too thick PLA layer. In order to solve these problems, the PLA is uniquely modified by Green Star to satisfy the strict demands. The modified PLA coated paper shows high heat-sealing property between paper and PLA, even the temperature of the tested water is as high as 100 °C. The weight per m² of the coated paper can be varied from 50~350g and no fracture was found during the following manufacturing process of cups or bags. Moreover, the PLA layer is thinner than other company’s products, which means the cost is lower. These high properties of the Green Star products would promote the application of PLA coated paper in global paper packaging market.