Near-Infrared Spectroscopic Evaluation of the Water Content of Molded Polylactide under the Effect of Crystallization
Near-Infrared Spectroscopic Evaluation of the Water Content of Molded Polylactide under the Effect of Crystallization
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DOI：
10.1177/0003702816681011
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发表时间：
2017-06-01
影响因子：
3.5
通讯作者：
Ohshima, Masahiro
中科院分区：
文献类型：
--
作者：
Muroga, Shun;Hikima, Yuta;Ohshima, Masahiro
在熔融加工过程中，聚乳酸（PLA）内部的水分容易引起水解，从而使产品的力学性能和热性能劣化。必须监测树脂颗粒的干燥状态，以防止PLA水解。在这项研究中，近红外（NIR）光谱法被应用于测量聚乳酸中的水含量。此外，近红外光谱的形状也会受到结晶的影响，这可能导致评估含水量的准确性降低。本研究的目的是建立一个稳健的模型，用于估计不同分散程度的结晶水含量。采用吸光度积分法和偏最小二乘（PLS）回归法两种方法估算干燥过程中测得的含水量，并考虑结晶的影响。从积分吸光度获得的含水量的校准线的斜率在具有不同堆叠的PLA之间变化。这是由于在5100- 5400 cm（-1）范围内，水的近红外吸收峰与聚乳酸晶体的近红外吸收峰重叠所致。我们发现，近红外光谱的形状被改变的结晶，和结晶度相比，薄片的厚度，是决定这样的变化的近红外光谱的主导因素。仅从无定形聚乳酸构建的水含量的PLS模型显示在结晶聚乳酸的估计误差大。相比之下，PLS模型构建的无定形和结晶PLA估计的水含量具有较低的误差。这是因为从无定形和结晶PLA获得的潜变量抵消了结晶对近红外光谱的影响。
During melt processing, the moisture inside polylactide (PLA) easily induces hydrolysis, which deteriorates the mechanical and thermal properties of the product. The state of dryness of resin pellets must be monitored to prevent PLA hydrolysis. In this study, near-infrared (NIR) spectroscopy was applied to measure water content in PLA. In addition, the shape of the NIR spectrum is also affected by crystallization, which could lead to a reduction in the accuracy of evaluating the water content. The objective of this research is to construct a robust model for estimating the water content with varying dispersive extents of crystallization. Two methods for estimating water content measured during a drying process were conducted: the integration of absorbance and partial least squares (PLS) regression were conducted to estimate the water contents in PLA considering the effect of crystallization. The slope of the calibration line of the water content obtained from integrating absorbance varied between PLA with different crystallinities. This is due to the overlap between the NIR band of water and that of PLA crystal in the range of 5100-5400cm(-1). We found that the shape of the NIR spectrum was changed by crystallization, and the crystallinity, compared to the thickness of lamellae, was the dominant factor determining such a change of NIR spectra. The PLS model of water content constructed from only amorphous PLA showed large error of estimation in crystallized PLA. In contrast, the PLS model constructed from both amorphous and crystallized PLA estimated the water contents with lower errors. This was because latent variables obtained from both amorphous and crystallized PLA cancelled the effect of crystallization on NIR spectra.