Effects of two different modified treatments were investigated relative to the chemical and mechanical properties of pretreated corn stalk particles and their composites prepared with a modified lignosulfonate (ML) binder. Corn stalk particles (CP) first were prepared by treating corn stalk particles with oxalic acid in ultrasonic conditions (pretreated corn stalk particles, PCP). These particles were then modified by treatment with either laccase-vanillin system with ultrasound (LU) or polyethylenimine-glutaraldehyde with ultrasound (PU), and the surface chemistries of the modified PCP and mechanical properties of LU-PCP/ML composites and PU-PCP/ML composites, such as modulus of rupture (MOR), modulus of elasticity (MOE), internal bonding strength (IB), 24-h thickness swelling (TS), and crystallinity were compared. Both modified treatments dramatically enhanced the mechanical properties of the composites. The MOR, MOE, and IB of the PU-PCP/ML composites were improved by up to 148%, 81%, and 62%, respectively, compared to LU-PCP/ML. Moreover, the 24-h TS of the LU-PCP/ML composites was reduced by 16%. These results show that the pretreatment method of CP and ultrasonic collaborative treatment of PCP can effectively improve the properties of its composites. Modified PCP with PU was more favorable for surface chemical and mechanical properties.
Recently, 9,10-anthraquinone(AQ) contamination in Chinese Liupao tea has attracted much attention because the tea for exportation must meet the EU limit(20 µg·kg-1). In this study, the sample pretreatment methods were optimized from the aspects of extraction reagent and purification column filler. Finally, n-hexane acetone was selected as the optimal extraction agent. When the content of Florisil in the purification column was 1.0 g, the purification effect was the best. The new method reduces the limit of quantification (LOQs) of AQ to 10 μg·kg-1, and the detection accuracy has also been further improved. The recovery of 9,10-anthraquinone-fortified tea samples (20-100 μg·kg-1) was 94.51-100.44%, and the relative standard deviation (RSD) was less than 1.31%. In this study, 98 Liupao tea samples on the market were tested by the new method. It was found that 61 samples were positive (occurrence rate 63.3%), and the AQ content of 55 positive samples was higher than the EU limit (20 µg·kg-1). This study also found that the pollution of AQ in Liupao tea increased with the growth of aging time. The source of AQ in the aging process of Liupao tea will be the focus of further research.
The outer surface of corn stalk (CS) plays a key role in the interfacial compatibility of non-wood-based panel products. To improve the bonding performance of the stalk surface, changes to the outer surface before and after four pretreatments (oxalic acid, oxalic acid + ultrasound, NaOH, NaOH + ultrasound) were investigated. Changes in the chemical composition, surface elements, aggregation structure, and microstructure of CS before and after pretreatment were analyzed. The results revealed that the wax layer, benzene–alcohol extract, and ash content of the outer surface of CS were decreased under different pretreatment conditions. The degree of reduction decreased in the order of NaOH + ultrasound > oxalic acid + ultrasound > NaOH > oxalic acid. The crystallinity of CS was obvious after pretreatment, and it increased in the order of oxalic acid + ultrasound > oxalic acid > NaOH + ultrasound > NaOH. Considering the properties of CS after pretreatment and the lignin activation modification of the CS surface, the optimal pretreatment conditions of CS were determined as oxalic acid + ultrasound, i.e., 5% oxalic acid and ultrasonication at 50 °C for 1 h.
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