On Natural Polymer Films for Packaging (I)

Abstract: Starting from the significance of green packaging, the following three basic types of starch, cellulose, and chitosan were used as raw materials to modify the properties of the polymer, and the properties of biodegradability and antibacterial properties were optimized. Polymer film.

Keywords: green packaging natural polymer membrane degradation antibacterial

Plastic packaging materials are widely used in the world because of their low cost, wide availability, and light weight. However, their shortcomings are also obvious. They are prone to produce harmful gases and odors and may be toxic to the human body; they are difficult to degrade in the environment after use. , causing serious white pollution u. Such as disposable snacks, the natural degradation of plastic materials used, the time required for more than 200 years.

The choice of packaging materials is an important factor in determining the size of packaging waste. The development of green packaging materials is the key to the final realization of green packaging. Developed countries compete for the development and production of biodegradable packaging materials and edible packaging materials that do not cause environmental pollution. They have long been using paper to package hamburgers, fast food, drinks, etc., and have the potential to replace plastic flexible packaging. China started late in this field, and research has only limited the preservation of edible liquid fresh-keeping coatings. There are few studies on the selection of film materials and film-forming properties of green packaging materials.

In addition, because packaged foods, fruits and vegetables and other nutrient-rich packaging materials are rich in nutrients, the conditions such as preservation temperature and humidity are also more suitable for the growth of microorganisms, so the surface of the packaging film is easily contaminated with microorganisms J, causing food, fruits and vegetables to rot. Mildew. If antibacterial materials are used to prepare the packaging film, the growth of microorganisms on the packaging can be suppressed, and the colonization and propagation of microorganisms on the surface of packaging materials can be prevented. This will further prevent deterioration of the product and improve the film packaging protection. Therefore, the development trend and implementation of basic green packaging materials are light and thin and highly functional (can be accommodated by the ecosystem, such as degradable packaging materials; or can be easily separated from the environment for recycling, etc.), only in this way To achieve the green packaging materials, environmental protection requirements.

1 Natural Polymer Materials

Natural polymers such as cellulose, starch, and chitin are rich in natural resources. Natural polymer materials that are naturally grown, naturally decomposed, and completely non-toxic are environmentally-friendly and meet the requirements and trends of environmental protection. All degradation into harmless substances, such as carbon dioxide and water L8. In addition, its own structure is diversified, and its intramolecular active groups can be selected with large selectivity. It is easy to adopt different modification processes to improve its processing performance, heat, properties and mechanical properties and impart other properties, such as antibacterial properties, to prepare a variety of structures. Lightweight and highly functional green packaging film.

1.1 Cellulose

In 1908, the Swiss chemist Jacques Brandenburg invented the cellulose film. This invention was called the most glamorous packaging invention in the 20th century. It invented the modern transparent flexible packaging and was widely used for fiber. Apply the foundation stone]. The natural state of the fiber-optic polymer chains has a tight, crystalline structure that is not easily soluble in neutral solutions. After chemical modification, methyl cellulose (Mc)EIo3, hydroxypropylmethyl cellulose (HPMC), hydroxypropyl cellulose (HPC) and carboxymethyl cellulose (CMC) can be made.

1.1.1 cellulose-based plastic film

The cellulose ether film prepared from the water or water-alcohol solution of MC, HPMC, HPC and CMC has suitable strength, grease resistance, flexibility, transparency, odorless and tasteless, soluble in water, and has good film formation. Characteristics, in fruits and vegetables and other food preservation has a significant effect, safe and non-toxic, colorless, odorless, easy to degrade and other excellent performance, especially suitable for "green food" packaging. The use of cellulose to prepare biodegradable materials opens up new sources of raw materials for the plastics industry. Therefore, researches on the properties and applications of cellulose membranes have received increasing attention.

Japan's four-country industrial laboratories have developed cellulose-based plastics for films, packaging materials, and other applications. They mixed latex-like cellulose with chitosan and dried them to obtain translucent flakes. In addition, the membrane materials made of cellulose and protein blends, membrane materials made from cellulose and its derivatives have good drying strength, wet strength is also satisfactory and the product cost is low, can be used for food, cosmetics, detergents And daily necessities packaging.

1.1.2 NMMO Process

The N-methylmorpholine mono-N-oxide (NMMO) process is a biodegradable green film processed by dissolving a natural cellulose raw material directly in a mixed solvent of a non-toxic NMMO and water. The process is simple, there is no chemical reaction in the whole production process, no gas is released, and the recovery rate of NMMO is very high, basically no waste, which avoids the problem of serious pollution in the traditional process, so it is called the green process. u6J. At present, foreign countries have successfully used this method to develop a green fiber-Lyoeell fiber. The fiber combines the excellent properties of natural fibers and synthetic fibers and enables the development of a variety of novel and unique products. In addition, the cellulose NMMO solution penetrates better into the paper network, making the paper-plastic reinforced casing more binding. A new method for making cellulosic films from cellulosic/NMMO stocks with more uniform film thickness, higher tear strength and tensile strength. Provides a new way for the development of green packaging materials and other materials.

1.1.3 Cellulose antimicrobial film

Cellulose has good biosafety and is widely used as a carrier of antimicrobial agents to prepare antibacterial functional polymer materials. Togami Su et al. fixed the small molecular disinfectant on the surface of the fiber cable by covalent grafting, and used the surface to contact the water for disinfection. It was confirmed that such a macromolecular antibacterial agent can effectively reduce the number of viable cells in the solution, and the antibacterial property and stability of the macromolecularized antibacterial material are greatly improved over the same structure of the small molecular monomer. We have shown here that we can graft a quaternary ammonium salt antibacterial group on the cellulose surface, and then use the NMMO process to form a new type of green aseptic fresh-keeping packaging film.

1.2 Starch

The starch itself is very brittle and should not be used as a degradable material alone. It must be physically modified or chemically modified to change its molecular structure, making it disordered and having thermoplastic properties. Starch and unsaturated monomers such as styrene, ethylene, propylene, acrylonitrile, acrylic acid and its esters and other copolymers can be formed into films. The developed starch membranes mainly include starch grafted methyl acrylate, propylene butyl ester and methacrylic acid. Methyl, styrene, etc.

1.2.1 Starch Edible Packaging Film

In recent years, starch edible packaging films have made important progress in the research and application of film forming materials and processes and plasticizers. The starch edible packaging film is the earliest type of research and development in edible packaging saliva, mainly based on amylose, polyols (such as glycerin, sorbitol, glycerol derivatives, and polyethylene glycol) and lipids (such as Fatty acids, monoglycerides, surfactants, etc.) are plasticizers, and a small amount of animal or vegetable gums are made as enhancers. They have the characteristics of stretchability, transparency, folding resistance, good water insolubility and low air permeability.