In recent years, with the development of new formats such as e-commerce, express delivery, and food delivery, the consumption of plastic shopping bags has shown a rapid upward trend, resulting in increasingly severe pollution to the environment. self
National standard for biodegradable plastic shopping bags (GB/T 38082-2019)Since its implementation over five years ago, in line with the national "plastic restriction order" policy, China has reduced traditional plastic products every year
plastic bagAbout 20 billion, equivalent to saving 1.2 million tons of oil resources and reducing carbon dioxide emissions by 840000 tons.
Biodegradable plastics refer to a type of plastic that is degraded by natural microorganisms under conditions such as soil and/or sandy soil, and/or specific conditions such as composting, anaerobic digestion, or aqueous media, and ultimately degraded into carbon dioxide (CO2) and/or methane (CH4), water (H2O) and their mineralized inorganic salts, as well as new biomass. The degradation mechanism of biodegradable plastics is shown in Figure 1. Promoting the use of biodegradable plastics instead of disposable non biodegradable plastics can to some extent solve the problem of plastic pollution.
Figure 1 Degradation mechanism of biodegradable plastics
At present, the main components of biodegradable plastic products in the market are polybutylene terephthalate (PBAT) and polylactic acid（
PLA）Made from two or more types of starch (ST), as well as inorganic fillers such as talcum powder (TALC) or calcium carbonate (CaCO3). Under the promotion of the Chinese government, significant progress has been made in biodegradable plastic technology in China. The technological level of biodegradable materials such as PLA, PBAT, and PHA continues to improve, and production costs gradually decrease, providing technical support for the widespread application of biodegradable plastic shopping bags.
1. Technological changes in biodegradable technology and compostable detection methods
The degradation performance testing methods include compostable degradation (GB/T19277.1, GB/T19277.2, etc.), freshwater environmental degradation (GB/T19276.1, GB/T19276.2, etc.), soil environmental degradation (GB/T22047), marine environmental degradation (GB/T40612, GB/T40611, GB/T40367, etc.), sludge anaerobic digestion degradation (GB/T 38737), and high solid state anaerobic digestion degradation (GB/T 33797).Composting method as an arbitration method in degradable detection technologyIt is widely used in the testing of biodegradable materials and products, and the testing standards are based onGB/T 19277.1-2025 "Determination of final aerobic biodegradability of materials under controlled composting conditions using method for determining released carbon dioxide - Part 1: General method"(ISO 14855-1:2012, IDT)。 The testing method has been officially implemented. This method simulates the typical aerobic composting treatment conditions of organic parts mixed into urban solid waste. The experimental materials are exposed to the inoculum generated by composting, and composting is carried out under environmental conditions where temperature, oxygen concentration, and humidity are strictly monitored and controlled. Measure the conversion percentage of carbon in the test material to the released carbon dioxide.
This article is based on the principle of composting testing to test and analyze the biodegradation rate and compliance of fully biodegradable plastic shopping bags (material: PBAT+PLA+ST).
2 experiments
2.1Materials and Equipment
Microcrystalline cellulose (thin layer chromatography grade), China National Pharmaceutical Group Chemical Reagent Co., Ltd; Fully biodegradable shopping bag, material: PBAT+PLA+ST, commercially available. Mature compost soil, with a fertilizer age of 2-4 months, commercially available.
AUTO GBDA-180 Intelligent Composting Degradation Tester, Guangzhou StandardTOC-L CPH+SM-5000A Total Organic Carbon Analyzer, SHIMADZU； PHS-3E Portable
PH meterThunder magnetism; GSX2-4-10G muffle furnace, Guangzhou standard; DHG-9030A air drying oven, Guangzhou standard.
2.2 Test Methods
2.2.1 Performance Testing
Total dry solids test: The proportion of the mass of the sample after cooling and constant weight under 105 ℃ air drying conditions to the original sample
Volatile solids (organic components) testing: The percentage of mass loss to the total dry solids content after burning the sample at a high temperature of 550 ℃
Total Organic Carbon Content (TOC) Test: Dry basis results were obtained using TOC-L CPH+Solid Sample Module SSM-5000A Total Organic Carbon Analyzer
Conduct tests on the total dry solids, volatile solids, total organic carbon, and pH of the docking material, reference material, and test material, respectively. Before using compost soil, remove large inert substances and screen with a 0.5 cm sieve. Cut the test material (plastic bag) into pieces with a maximum surface area of no more than 2cm * 2cm. The processed sample is shown in Figure 2.
Figure 2: Pre treated reference materials, experimental materials, and inoculum
According to the requirements of GB/T19277.1-2025 and GB/T 38082-2019 standards, the sample pretreatment and indicators are shown in Table 2, and the sample test results are shown in Table 3.
Table 2 Appearance and Indicators of Samples
Table 3 Sample Test Results
2.2.2 Controlled Industrial Composting Test
Based on the standard GB/T19277.1-2025, biodegradation performance testing was conducted under aerobic industrial composting conditions. The experimental temperature is 58 ℃± 2 ℃, and the moisture content of the inoculum is controlled at 50%~55%. The sample material (or reference material) and inoculum are thoroughly stirred and mixed in a dry weight ratio of 1:6, and loaded into the reaction vessel. The experimental process requires sufficient aeration, with an oxygen concentration of not less than 6%, and regular mixing. Blank test, reference test, and sample test each require testing 3 parallel samples and taking the average. During the routine 45 day to 6 month experimental period, a continuous infrared carbon dioxide sensor is used to quantitatively test the carbon dioxide content emitted from each composting container. The ratio of the cumulative carbon dioxide release after deducting the blank to the theoretical carbon dioxide release is the biological decomposition rate.
3 Results and Discussion
The test material for this test reached a relatively stable state in the biodegradation rate curve after 128 days of testing, and the test was terminated. According to the requirements of GB/T38082-2019, the relative biodegradation rate of the mixture should be ≥ 90%. The relative biodegradation rate is the ratio of the sample biodegradation rate to the reference biodegradation rate. The biodegradation rate of the reference material in this experiment is 89.34%, the biodegradation rate of the experimental material is 81.27%, and the relative biodegradation rate is 90.97%, which meets the standard requirements for biodegradation rate indicators. The carbon dioxide emissions of the test materials and reference materials during the experimental period are shown in Figure 3, and the biodegradation rate is shown in Figure 4.
Figure 3: Carbon dioxide emissions from experimental and reference materials
Figure 4: Biodegradation rates of experimental and reference materials
In the composting experimentearlyThree key indicators require special attention:
(1) After 45 days, the decomposition rate of the reference material exceeded 70%;
(2) During the experiment, the relative deviation of the biodegradation rate of each compost container shall not exceed 20%;
(3) Within the first 10 days of cultivation, the blank container produces 250mg~150mg of CO2 per gram of volatile solid (average) inoculum. Only when the experiment meets the indicators can it be recognized as valid.
The experimental period is relatively long, with a temperature maintained at 58 ℃. The inoculum is prone to dehydration and agglomeration, requiring regular replenishment of distilled water and regular stirring to ensure that the inoculum and material mixture are in a moist state with a moisture content of about 50%, which is beneficial for the effective activity of microorganisms.
Although there are currently many rapid detection technologies available in the degradation detection market, utilizing material characterization techniques such as FTIR, DSC, etc. for rapid component analysis. However, a single characterization method cannot accurately identify the composition of mixed materials/products, nor can it determine whether the biodegradation rate meets the standard. Testing using composting methodSingle material or mixed materialBiodegradable products are still one of the most authoritative methods at present.
The quantitative methods of composting include titration, weight method, gas chromatography, continuous infrared analyzer, etc. In order to solve the problems of long testing time, high cost, and manual monitoring, it is recommended to use intelligent equipment with continuous infrared carbon dioxide sensors for quantitative testing to complete the degradation performance testing of biodegradable materials/products. It can achieve intelligent monitoring of the entire process, automatic temperature control, regular mixing, sufficient aeration, and automatic judgment of data validity. During the experiment, the daily carbon dioxide generation and degradation rate data of each composting container, as well as the released carbon dioxide curve and biodegradation rate curve, can be directly exported for final reporting. Helps to improve the quality and efficiency of compostable degradation testing projects.
