KEYWORDS
- Cellulose, lignin, hemicellulose
- NIR Spectroscopy
- Pulp, paper
TECHNIQUE
Near Infrared spectroscopy
Introduction
The pulp and paper industry produces cellulose-based products from various types of wood. Wood, the source of paper, is mainly composed of cellulose, hemicellulose, and lignin. Different microstructures in wood allow wood to be classified as softwood or hardwood. Usually, softwood is often used for production.
Each step in the wood production process is important in determining the quality of the final paper product. So being able to screen and monitor various quality control parameters before, during, and after the production process is extremely important to create high-quality paper products for users.
In the pulp and paper industry, the accurate determination of hemicellulose, cellulose, and lignin content in wood and pulp materials is crucial for optimizing process efficiency and ensuring the quality of the final product.
Traditional wet chemistry methods are time-consuming, chemical reagent-intensive, and labor-intensive, and cannot be detected quickly and in real time.
Therefore, near infrared spectroscopy (NIR) has recently been recognized as one of the most promising techniques for predicting the physical and chemical properties of bulk materials, due to its simple, fast sample preparation. Fast, non-destructive, and has good reproducibility. NIR has been used to analyze the components of wood, corn stalks, and straw. It promises to be an extremely widely applied technique in the paper manufacturing industry.
EXPERIMENTAL METHODS
Near-infrared spectroscopy (NIRS) is an excellent method for quantifying certain chemical parameters such as water content (moisture), hemicellulose, cellulose, and lignin content because it is sensitive to the presence of certain functional groups. Since this interaction also depends on the sample matrix, NIRS also facilitates the detection of other physical parameters such as density and intensity.
NIR spectroscopy can provide structural information on biomass components by analyzing broad and highly overlapping NIR absorption peaks.
Depending on the substances that need to be analyzed, there will be different characteristic peaks to observe the absorption spectrum. With hemicellulose there will be 22 characteristic wavelengths, cellulose is 22 and lignin is 20 selected by SPA similar to Figure 1 below.
Figure 1: Distributions of the characteristic wavelengths selected by SPA for hemicellulose (a), cellulose (b), and lignin (c).
At the same time, combined with some data preprocessing algorithms will help quantify compounds more quickly and accurately. Specifically, it is necessary to remove abnormal samples of hemicellulose, cellulose, and lignin using PLS. NIR spectra are often affected by factors such as background noise, light scattering, and sample inhom*ogeneity. Therefore, it is often necessary to appropriately pre-process spectral information to remove the influence of confounding factors. And apply the validated calibration models to predict the hemicellulose, cellulose, and lignin content in unknown samples based on their NIR spectra
With this method, the results of predicting the content of hemicellulose, cellulose, and lignin are very positive with high determination coefficients of 0.93, 0.9, and 0.89, respectively.
These results demonstrate that NIR spectroscopy combined with intelligent algorithms is a useful, non-destructive tool for the determination of hemicellulose, cellulose, and lignin.
RECOMMENDED EQUIPMENT
For applications using Near-infrared spectroscopy (NIRS), INTINS offers the Ocean Optics NIRQuest+ spectrometer product line with high sensitivity and good resolution from 2.8 nm to 6.48 nm. NIRQuest+ is available in three versions covering different wavelengths from 900-2450 nm.
NIRQuest+ can measure very small changes in absorbed signal, which are typical of harmonic overtones in the NIR. Its higher sensitivity enables better measurement accuracy, particularly in low-light conditions. Also, at longer wavelengths, NIRQuest+ measures diffuse reflection at low noise levels, resulting in cleaner spectra at wavelengths where distinct spectral features can be difficult to capture.
Figure 2: NIRQuest+ Spectrometer
At the same time, we can provide other accompanying optical devices such as fiber, light sources... suitable depending on the customer's application needs.
In addition, the system comes with extremely convenient and easy-to-use software. A full combination of necessary features helps users easily observe the spectrum of paper samples on the line in real-time. At the same time, real-time analysis capabilities of NIRS allow for rapid monitoring of hemicellulose, cellulose, and lignin content throughout the pulp and paper process, enabling timely adjustments to optimize process parameters and product quality. Qualitative and quantitative results of QC parameters are output on a fast, intuitive screen.
CONCLUSIONS
Near Infrared Spectroscopy offers a reliable and efficient method for the determination of hemicellulose, cellulose, and lignin content in pulp and paper materials. By providing rapid, non-destructive analysis capabilities, NIRS can significantly enhance process control and product quality in the pulp and paper industry. Implementation of NIRS for routine analysis can lead to cost savings, improved efficiency, and better overall management of the pulp and paper process. It is also environmentally friendly and user-friendly facilitating simultaneous analysis of several key quality parameters in just a single scan.
NIRS is also verified for quality control purposes by standards organizations such as ASTM. Furthermore, it can be operated by people without technical expertise, as its user-friendliness sets it apart from more complex analysis techniques.
