In this paper, the degradation behavior of two kinds of polylactic acid (PLA) biodegradable material products (pure PLA cup cover and modified PLA straw) was studied. It was found that under the composting environment specified in the International Standard, in the first 35 days, the degradation rate of the straw (with 50%-60% poly butylenes succinate (PBS)) was faster than that of the pure PLA cup cover, but in the later stage, the PLA cup cover exceeded the straw and disintegrated preferentially, and both could be degraded in about 70 days. After further analyzing the far-infrared (FIR, can also be called THz) and mid infrared (MIR) spectra of cup cover and straw, we observed that the material structure had not changed until disintegration, only the ester bond was hydrolyzed, the polymers became oligomers, which could be reflected in the change of the effective area of the characteristic peak at 7.15 THz (cup cover, labeled 1921) and 6.99 THz (straw, labeled 4386) in the THz spectrum. With the degradation, the effective area decreased continuously. Due to the strong absorption of the material in MIR band, most characteristic peaks were flattened and lost analytical value. The bivariate correlation of degradation time, biodegradation rate, total carbon dioxide release and the effective area of the characteristic peak at 7.15 THz (1921) and 6.99 THz (4386) in THz spectrum was analyzed by SPSS software. We discovered that the degradation time was significantly positively correlated with biodegradation rate and carbon dioxide release at the level of 0.01 and negatively correlated with the effective area of characteristic peak at the level of 0.05. The biodegradation rate was significantly negatively correlated with the effective area of characteristic peak at the level of 0.01. Taking the degradation time as the independent variable and the biodegradation rate, carbon dioxide release and effective area of characteristic peak as the dependent variables, we got that the THz spectrum could be used to describe the degradation behavior of PLA products as long as appropriate coefficient correction was made. In this way, we could separate from the laboratory environment, study the impact of environmental diversification on material degradation performance, and reduce the cost of material degradation performance identification. Using density functional theory (DFT), reduced density gradient (RDG) method and visualization software, the changes of weak interaction position and intensity in the molecule during the polymerization of lactic acid into PLA were further analyzed. We found that the vibration of ester bond corresponded to the characteristic peak with weak intensity in the spectrum, and the peak with large intensity mainly originated from the out-of-plane swing of O-H bond in the molecule.

本文研究了两种聚乳酸（PLA）生物降解材料产品（纯PLA杯盖和改性PLA吸管）的降解行为。发现在国际标准规定的堆肥环境下，前35天，秸秆（含50%-60%聚丁二酸丁二醇酯（PBS））的降解速度快于纯PLA杯盖，但后期PLA杯盖超过吸管优先解体，70天左右即可降解。进一步分析杯盖和吸管的远红外（FIR，也可称为太赫兹）和中红外（MIR）光谱后，我们观察到材料结构直到解体才发生变化，只有酯键水解，聚合物变成了低聚物，这可以反映在太赫兹光谱中7.15 THz（杯盖，标记为1921）和6.99 THz（稻草，标记为4386）处特征峰有效面积的变化。随着降解，有效面积不断减小。由于材料在中红外波段的强吸收，大多数特征峰变平并失去分析值。采用SPSS软件分析了太赫兹光谱中7.15 THz（1921）和6.99 THz（4386）特征峰的有效面积与降解时间、生物降解速率、总二氧化碳释放量的双变量相关性。我们发现降解时间在0.01水平与生物降解率和二氧化碳释放呈显着正相关，在0.05水平与特征峰有效面积呈负相关。生物降解率与特征峰有效面积呈显着负相关，在0.01水平。以降解时间为自变量，以生物降解速率、二氧化碳释放量和特征峰有效面积为因变量，只要进行适当的系数校正，太赫兹光谱可用于描述PLA产品的降解行为。被制作了。这样就可以脱离实验室环境，研究环境多样化对材料降解性能的影响，降低材料降解性能鉴定的成本。使用密度泛函理论 (DFT)、降低密度梯度 (RDG) 方法和可视化软件，进一步分析了乳酸聚合成PLA过程中分子内弱相互作用位置和强度的变化。我们发现酯键的振动对应于光谱中强度较弱的特征峰，而强度较大的峰主要来源于分子中OH键的面外摆动。