What is the detection process for the biodegradation rate in the quality inspection of PLA non-woven fabric?

In the quality inspection of PLA non-woven fabric, the biodegradation rate is one of the core indicators. Its detection requires simulating specific environments (such as industrial composting, soil, water, etc.), and is determined by measuring the degree of degradation of the material under the action of microorganisms (such as the proportion of carbon elements converted into CO₂). At present, the standard methods commonly adopted both internationally and domestically are mainly based on industrial composting conditions (as PLA non-woven fabric is mostly used in disposable scenarios and needs to degrade rapidly in a controllable composting environment). The following are the specific testing methods and processes

I. Core Testing Standards: The biodegradation rate testing must be based on authoritative standards to ensure the consistency and comparability of the results. Commonly used standards include: • International standards: ISO 13432 "Packaging Materials - Test methods and Requirements for compostability and biodegradability", ASTM D6400 "Standard Specification for Compostability of plastic materials for Municipal or Industrial Composting Facilities". • Domestic standards: GB/T 19277.1-2011 "Determination of Final Aerobic biodegradation and disintegration Capacity of Materials under Controlled Composting conditions - Part 1: General Methods", GB/T 28206-2011 "Technical Requirements for Compostable Plastics". These standards have clear regulations on the testing environment, the source of microorganisms, the testing cycle, etc. (For example, industrial composting conditions: temperature 58±2℃, humidity 50%-60%, and the inoculum is compost maturity).

 Specific Testing Process (taking ISO 13432 as an Example)

1. Sample Preparation • Cut the PLA non-woven fabric into fine particles (usually ≤10mm), accurately weigh the sample mass (denoted as m, unit: g), and calculate its carbon content (determined by elemental analysis, denoted as C_sample).

At the same time, prepare "positive controls" (such as cellulose, which is known to be 100% degradable) and "blank controls" (containing only compost inoculants and buffers, without samples) to verify the effectiveness of the detection system.

2. Inoculation materials and Reaction system Construction

• Inoculation materials: Municipal sludge or compost products (containing natural microbial communities) are used and mixed with distilled water and buffer solution (maintaining pH 7.0±0.5) in standard proportions to form the reaction substrate.

• Reaction vessel: Use a closed respiratory metering instrument (such as a constant pressure or constant volume system) to mix the sample, positive control, and blank control with the inoculated matrix respectively, and place them in a constant temperature incubator at 58±2℃.

3. Degradation process monitoring and CO₂ collection

• Continuously monitor the CO₂ produced by the reaction system within 6 months (the maximum detection period required by the standard) : ◦ If it is a constant pressure system, calculate the output by measuring the volume of CO₂ gas (after drying and removal of interfering gases); If it is a constant volume system, the output is calculated by measuring the change in CO₂ concentration in the gas (such as an infrared detector). The CO₂ produced by the blank control should be deducted from the sample group (excluding the interference of self-degradation of the inoculated substances).

4. Calculation of Theoretical CO₂ Quantity: Based on the carbon content of the sample, calculate the total amount of CO₂ that should be produced when it is completely degraded: Theoretical CO₂ quantity (g) = (C_sample × 44) ÷ 12 (Note: 44 is the molar mass of CO₂, and 12 is the molar mass of carbon, that is, 1g of carbon is completely converted into 1× 44/12g of CO₂.

5. Biodegradation rate determination: When the biodegradation rate of the positive control is ≥70% (indicating the effectiveness of the system), and the biodegradation rate of the sample within 6 months is ≥90%, it is determined to be "biodegradable". If 90% is not reached within 6 months, the testing period should be extended to 2 years (but PLA, as a degradable material, usually meets the standard within 3 to 6 months).