Polycarbonate (PC) plastic is a universal engineering plastic containing carbonate groups, widely used in various industries such as building materials, automobile manufacturing, medical equipment, etc. China is a major producer and consumer of PC.
With the upgrading of PC products, the amount of waste PC plastic is huge. Recycling and reusing is an important measure to build a circular system. However, recycled PC will release volatile odors during storage, which can be harmful to human health and the environment.
The article establishes an objective odor evaluation method to control the quality of recycled PC plastic by analyzing its odor.
01
AIRSENSE electronic nose
AIRSENSE electronic nose is a compact, fast, and efficient detection system consisting of a sensor array, signal preprocessing circuit, and computer pattern recognition system. Its sensor array includes multiple metal oxide gas sensors, which can accurately detect various volatile substances such as aromatic compounds, hydroxyl compounds, ammonia, etc. In the study of odor analysis of recycled polycarbonate (PC) plastics, the W1S sensor in its sensor array is sensitive to methyl substances, the W1W sensor is sensitive to sulfides, and the W2S sensor responds significantly to alcohol and aldehyde ketone components, accurately capturing key components in complex odors.

02
Details of the experimental plan
1
Experimental materials
9 types of commercially available recycled PC plastics, details are shown in the table below

2
instrument and equipment
Airsense's electronic nose from Germany contains 10 metal oxide sensors with varying sensitivity to different volatile compounds.
3
Experimental steps
According to the requirements of CB/T40006.1-2021, weigh (20 ± 0.1) g of the sample into a wide mouthed glass bottle, seal it tightly, and place it in a constant temperature chamber at (80 ± 2) ° C for (120 ± 10) minutes. After cooling to (60 ± 2) ° C, use an electronic nose for odor measurement.
Determine the optimal testing conditions for electronic nose testing of regenerated PC plastic odor by setting parameters such as sensor cleaning time, zeroing time, data acquisition time, and injection flow rate. The optimal testing conditions established through single factor experiments are sensor cleaning time of 80 seconds, zero adjustment time of 5 seconds, data acquisition time of 120 seconds, and injection flow rate of 400 mL/min.
03
Experimental results and analysis
Sensor response analysis

The sensor response first increases and then decreases because odor components first accumulate on the sensor surface, and then the adsorption rate is lower than the volatilization rate.
The data collection time of 120 seconds can obtain high response values from various sensors, with W1S (sensitive to methyl groups), W1W (sensitive to sulfides), and W2S (sensitive to alcohols, aldehydes, and ketones) showing significant odor response to regenerated PC.
Fingerprint analysis

Select first level, second level, and third level recycled PC plastics and draw odor fingerprint maps. The response values of W1S, W1W, and W2S sensors follow a three-level>second level>first level pattern, while the maximum response values of other sensors basically overlap; The reasons include the degradation of sulfur-containing flame retardants to produce sulfides, the degradation of PC to produce aldehydes and ketones, and the breakage of isopropylidene chains to produce methyl products. Moreover, the more regeneration times, the greater the response value of easily degradable components.
Principal Component Analysis (PCA)

For three types of recycled PC plastics, a model was established by selecting the high response areas of sensors at 62, 63, 64, and 65 seconds. The principal component contribution rate was 99.46%, the second principal component was 0.53%, and the total contribution rate was 99.99%. The recognition ability of the three samples was 1, and they were separated in the PCA diagram. The distance between the first and third levels was far, and the odor difference was large, which was consistent with manual odor recognition.
For 9 types of recycled PC plastics, the main component contribution rate is 70.51%, the second main component is 28.94%, and the total contribution rate is 99.45%. The recognition ability of all 9 samples is>0.99, and odor differences can be distinguished; The order of odor intensity is consistent with manual odor recognition, and the odor of third grade regenerated PC is strong. The odor of similar second grade regenerated PC is greater than that of first grade, and PC/GF has a stronger odor due to the characteristics of glass fiber.
04
research findings
The AIRSENSE electronic nose data collection time is set to 120 seconds to obtain high response values of each sensor to the odor of regenerated PC, and the electronic nose is most sensitive to methyl, sulfide, alcohol, and aldehyde ketone components.
Extracting the odor fingerprint map drawn from the high response values of each sensor can intuitively analyze the differences in odor of recycled PC plastic.
The PCA model based on sensor response signals can effectively distinguish the differences in odor response values of different recycled PC plastics, and can also distinguish the size of odors, which is consistent with the results of manual odor recognition.