Talking about the Development and Application of Green Food Packaging Film (I)

Abstract : This paper summarizes the current development of green packaging films at home and abroad, and introduces the research progress of edible films, biodegradable films and water-soluble films and their applications in food packaging. With the continuous improvement of materials and processing technology, plastic flexible packaging has been in many areas of production and living. People's lives can not be separated from shopping bags, commodity bags, garbage bags, refrigerator storage bags; and industrial products packaging, household daily goods packaging, clothing packaging Pharmaceutical packaging also uses plastic flexible packaging films in large quantities. However, the negative impact of packaging waste on people's lives and the harm caused to the environment have also intensified. Nowadays, as people's awareness of environmental protection continues to increase, consumers place higher and higher demands on the packaging of goods. The demand for green packaging is also expected to increase. The so-called green packaging refers to moderate packaging that can be recycled, reused, or degraded in nature, and that does not cause harm to the human body and the environment throughout the product's life cycle. The greening of plastic flexible packaging films has become one of the important trends in packaging materials. Edible films, degradable films, and water-soluble films are green packaging products that have been researched and developed in various countries in recent years.

1. Edible film

The edible film is a film with a porous network structure formed by natural molecular interactions (eg, polysaccharides, proteins, etc.) as raw materials through the interaction of different molecules. Edible films have long been known as starch films made from starch. The earliest starch films used in packaging in China are commonly known as glutinous rice paper and have been commonly used for candy packaging in production. Even candy can be eaten together. The edible film can be applied to the inner packaging of various foods, such as wrappings for wrapping candy, sticky pastries, or forming casings, fruit clothes, and capsules. It also caters to the rapid and convenient consumption of modern consumption and has a huge market in the food industry. For instant noodle soup packed in edible film, it can be directly dissolved in water. It is no longer necessary to remove the outer (paper) packaging. The edible film itself has nutrition and flavor. The raw materials for the preparation of edible films are classified into cellulose derivative membranes, protein membranes, and starch membranes.

Cellulose derivative membrane:

The most common edible films made from cellulose derivatives are methyl cellulose (MC), hydroxypropylmethyl cellulose (HPMC) and hydroxypropyl cellulose, and dissociable carboxymethyl groups. Cellulose sodium and so on. In recent years, the research and development of modified cellulose edible films has received great attention in various countries in the world. Japan recently introduced edible film made from bean dregs as a raw material for the packaging of instant noodle sauces. U.S. production and research institutions have also succeeded in producing edible cellulose membranes using hydroxypropylmethyl cellulose (HPMC). Some people in China also fully dissolved methyl cellulose, coated and dried to make edible films. The edible film has high strength, moisture resistance, and high gas barrier; they also use methyl cellulose and carboxymethyl cellulose. As raw materials, stearic acid, palmitic acid, beeswax and agar are used as plasticizers and reinforcing agents to make them translucent, soft and smooth, and the entrance is ready, the mechanical strength is high, and the breathability and moisture permeability are less edible. membrane.

Protein film:

Both animal protein and vegetable protein can be used as raw materials for edible membranes. Protein itself is an essential nutrient for the human body and has good safety. This is the advantage of protein membranes. The animal protein is derived from animal skin, bone, cartilage tissue, etc. Such films such as protein casings have better strength and water resistance, and are suitable for packaging of meat foods. Edible films based on plant proteins mainly include soy protein isolate films, zein films, wheat gluten protein films and whey protein films. The vegetable protein film extracted from soybeans, etc., has good moisture-proof and oxygen-blocking ability, and has certain antibacterial properties, and is suitable for packaging of fat-containing foods. The edible film made from soy protein isolate as base material, sodium carboxymethyl cellulose as enhancer, and glycerin as plasticizer has good mechanical properties and can be used for powder packaging of bean flour, seasoning powder, etc. Instant edible, safe and hygienic; Modified corn gluten film, its water vapor permeability is equivalent to corn gluten film with a small amount of plasticizer added, and it obviously improves its mechanical properties. Starch film; Starch-based edible films have the advantages of low cost, high transparency, and are increasingly valued by people. Starch starches such as potato, sweet potato, and tapioca starch are generally suitable for starch. Starch, such as wheat and corn, has poor viscosity and malleability and should not be used alone. It must be used together with agar and carrageenan. Amylose can be used to make water-permeable membranes with low oxygen permeability. For example, hydroxypropyl starch has high crystallinity and high binding energy density. Therefore, its oxygen permeability is lower, especially valuable is high amylose film. In high temperature environments, the barrier properties will not decrease, and the packaged foods and the like can be effectively protected. Most of the edible films currently researched are based on corn starch. There are also some composite membranes such as chitosan and corn starch, which are insoluble in water and have high tensile strength. Cross-linking corn starch and pea starch film with phosphorus oxychloride can significantly improve the mechanical properties of the membrane; corn starch Acetate film, this film has better film forming performance and process performance.

In recent years, many countries in the world have made great progress in the study of edible films, and the application of edible films has become more and more widespread. However, currently edible films still have more processability, mechanical strength, and protective functionality than plastic films. Poor, high costs and other deficiencies, with the in-depth research and development, to overcome the above shortcomings, I believe that edible film packaging will have greater development.

2. Degradable film

The biodegradable film mainly solves the problems of waste and non-degradable packaging materials being difficult to recover, buried in the ground to destroy the soil structure, and incineration treatment will produce toxic gases causing air pollution. The biodegradable plastic packaging film not only has the functions and characteristics of traditional plastics, but also can be divided and degraded in the natural environment through the action of microorganisms in the soil and water or the action of ultraviolet rays in sunlight after the service life is completed. Domestic research and development of the variety has covered photodegradation, biodegradation, photo-biological double degradation, high calcium carbonate filled photo-oxygen degradation and other major categories. Photodegradation:

According to the basic principle of photochemistry, ethylene-based polyolefins are relatively stable under ultraviolet irradiation, and pure ethylene-based polyolefins do not contain chromophores that absorb ultraviolet photons, so under light irradiation, the degradation process takes a long time. Studies have shown that if the molecular chain of the polyolefin contains >C=O, it can absorb ultraviolet rays with a wavelength below 340 nm, causing photodegradation. Therefore, in the olefin monomer, a small amount of a carbonyl group-containing monomer is added and after copolymerization, the resulting polymer copolymer is very prone to photodegradation. The commonly used carbonyl-containing comonomer is carbon monoxide and ketones, and methyl vinyl ketone (MVK) and methacryloyl ketone (MIPK) are the most commonly used ketone monomers. In polyethylene or polypropylene, as long as a small amount such as an ethylene-CO copolymer or an ethylene-MVK copolymer is added, a photodegradable film can be obtained by a conventional method.

In addition, in ordinary plastics, a small amount of photosensitizer is added, and a photodegradable plastic film can be obtained by conventional methods. Commonly used photodegradation accelerators are acetylacetone complexes, aryl ketones, copolymers containing benzophenone and its derivatives, dithiocarbamates, halogen compounds, dodecyltrimethylammonium Diacid esters, ferrocene and its derivatives.