The arguments and development analysis of biodegradable packaging materials III

5. Aliphatic polyesters and polyesteramides

The widely used varieties in general-purpose plastics are PET and PBT, which are made from petrochemical raw materials and cannot be biodegraded. After the 1960s, it was found that aliphatic polyesters can be biodegraded. Correct choice of dicarboxylic acids and glycols (or lactones) can synthesize fully aliphatic polyesters. At the same time, the availability of such polyesters must be considered. The melting temperature is higher than 80°C, and the crystallization temperature must be restricted. . Polybutylene succinate (PBS) has a melting point of 114° C. and crystallized at 75° C. The mechanical properties of films prepared by blow molding are similar to those of low density polyethylene. In the copolymerization of adipic acid, PBSA copolymers can be prepared. Since the crystallinity is reduced, the degradation rate is increased, but the low crystallization temperature also has disadvantages. Both PBS and PBSA were developed and put on the market by Japanese electricians under the trade name Bionlle. Both nylon 6 and nylon 66 in polyamides have been produced on a large scale. Like PET, the rate of degradation of semicrystalline polyamides is very slow. However, there are a certain amount of ester components in the polyester amide molecules, and amide components are randomly distributed therein, wherein the ester composition is biodegradable. The ε-caprolactam copolymer (ε-caprolactam 60%) has a melting temperature similar to that of low-density polyethylene and is suitable for producing a film. The copolymers of hexamethyldiamine, adipic acid, butanediol and diethyl glycol (amide content 40 wt%) are relatively rigid and suitable for the production of injection molded parts such as flower pots, disposable cutlery and fibers. Since petrochemicals can also synthesize lipid polyesters like PBS and PBSA, these polymers can pass the German standard test method DIN V54900, which is a biodegradable polymer. Bayer sold its polyester amides under the BAK brand from 1991 to 2001. Because of its high cost, petroleum-based polymers have poor biodegradability. Due to the issue of material legislation for the manufacture of renewable resources in Germany, the company abandoned the business.

6. About Lipids - Cyclic Polyesters

Many companies have recently marketed copolyesters synthesized from adipic acid and terephthalic acid with butanediol (Ecofiex from BASF, Biomax from DuPont, and Easter Bio from Eastman Chemical). Compared with conventional terephthalic acid copolymers (PET and PBT), such lipid-ring copolyesters can be biodegraded, but the stiffness ratio of the chain is entirely greater than that of the aliphatic polyesters. The monomers used are all manufactured from petrochemical routes. Ecoflex is a random copolymer containing equal amounts of adipic acid and terephthalic acid. The glass transition temperature is about -30°C and the melting point is 110-115°C. The physical and mechanical properties of this soft thermoplastic are similar to those of low density polyethylene and can be processed using LDPE's common processing equipment. This material is marketed as a decomposable packaging film and can be used as a farm film, and can also be used as a hydrophobic protective coating and blending material for foamed starch and paper food containers. Copolymers containing higher TPA components are suitable for making fibers. Ecoflex is currently manufactured by BASF's pilot plant with an annual output of 8000 tons. It can also be passed the German DI-NV5400 standard and is considered biodegradable. Its complete hydrolysis to monomer may be under investigation, and it is expected that the metabolic process can be further completed to CO2 and water. In 2002, it was reported that cobalt-catalyzed alternating copolymerization using CO and propylene oxide to synthesize biodegradable polyhydroxybutyrate (PHB) yielded a molecular weight of 5×10^4 gm-1 polymer, which is yet to be determined. Process scale up to industrial scale. However, this result shows that, through new reactions, PHB is converted to microorganisms based on classical petrochemicals.

7. Controversy about degradability and raw material basis

Raw materials for biodegradable materials can be made from renewable resources, and can also be synthesized on the basis of petrochemicals. Which kind of raw material is more reasonable is a problem that is currently being debated in the academic and industrial circles. From a business perspective, price is a major factor in achieving success. Although consumers may be willing to pay more for biodegradable packages, this willingness is very limited. At present, various consumer products claim to have ecological benefits. Whether it is true or not, people will not be willing to increase expenditures for this purpose. Polymer resin prices are often a direct reflection of raw material cost production economies of scale and marketing strategies. Current pricing has no guiding significance.

Ecoflex is produced at a test volume of 8,000 t/a. The current price is 3.1 EUR/kg, which has entered the price range of engineering plastics. PLA, produced by Cargil Dow, is large and can currently be sold for less than €2.2/kg. In the past few years, the price of PET floated between 1-1.5 euro/kg, and the current price of polyethylene was about 0.8 euro/kg. Biodegradable polyesters (manufactured with renewable resources) should first be sold at prices close to that of generic plastics. To exert influence on legislation, for example, Germany's mandatory reduction of the cost of abandoning biodegradable materials for biodegradable waste (collection of waste in German cities) reflects its preference over conventional plastics.

Of course, there are still controversies about the ecological benefits of this sort of collection of waste from renewable resource products. PLA is an example of a closed cycle that can be considered from raw material to product until after use. However, this cycle does not take into account the energy used in fertilizer and pesticide production, raw material and intermediate transportation, and processing. According to calculations, approximately 57 MJ (a considerable amount of fossil fuel) is required to produce polymer from CO2 and water. The production of 1kg PET or LDPE requires energy consumption of 80MJ (equivalent to 2kg of crude oil), half of which is used as raw material for imported products. The amount of CO2 formed in the synthesis of PLA is greater than that in the synthesis of PET or LDPE and can roughly correspond to the consumption of raw materials for photosynthesis in biomass. Therefore, from the point of view of overall balance, PHB produced with microorganisms is not superior to products currently produced with other technologies. Considering the full life cycle of a polymer, its decomposition is gradual and not the most beneficial. Incineration can provide energy, but it emits considerable amounts of CO2, but it is buried underground without CO2 release. (Organic waste fermentation can produce methane, As an energy source, it has a good energy balance, but it is not yet widely used).

It is a controversial proposal to bury the waste generated from renewable resources underground to improve global CO2 balance. Although they can be degraded, the degradation rate is very slow, which is a problem worth noting. Although biodegradable materials made from renewable resources can provide certain ecological benefits, it cannot be used as a "green" product by itself. For polymer synthesis, fuels that provide energy are more decisive than resources that are used as raw materials. If the total energy demand, most of it can be provided by non-mineral resources, such as wind, solar or hydraulic power, and nuclear energy that is still in dispute. Polymers made from renewable resources may have advantages over petrochemical polymers.

Cargil Dow has announced that wind power will be used in future PLA production, and that plant wastes such as straws and blades will replace corn, thereby improving its ecological and economic balance. These wastes contain cellulose and hemicellulose and can be used as raw materials. Lignin can be burned to produce energy. From the perspective of the overall social level, it must be done between different factors such as greenhouse gas emissions, environmental pollution caused by pesticides, oil and gas production pollution, decomposition of wastes, or the release of pollution sources buried in the decomposition of underground waste, reduction of cultivated land, and the willingness not to spend more. balance. At present, some countries, such as the European Union, have established a very complete management system and provided a rigorous framework. Regardless of the above considerations, the development of biodegradable materials in the past 10 years has made progress, and has occupied its own position in some applications that strictly require biodegradability. The aforementioned several polymers have been obtained as detachable bags and agricultural films. A lot of applications. Moreover, the new polymers, PLA and aliphatic chain monocyclic polyesters have also exceeded the limits of degradation and raw materials, and have gained attractive material status with their various good properties.