Evaluating the performance of hemp bast fibres in the production of packaging paper using different …
According to Chieng et al. [2017], the degradation in cellulose, hemicellulose, and lignin after certain treatments is relevant to the change in fibres, and degradation is also associated with weight loss and changes in the chemical compositions of fibre. The yield of a given raw material is a very important factor that influences the profitability of processing the fibre source. The calculated pulping yields for the two batches were 70.4% and 71.2%. The average value was 70.8%, which is a high yield value for cooking. According to Cheremisinoff and Rosenfeld [2010], the yields between 40% and 55% ranged as low. According to the study results of Danielewicz and Surma- Ś lusarska [2010], hemp bast fibre kraft pulp has a higher yield than commonly used woods. In their study, they evaluated the kraft pulping yields of hemp bast fibres, birch and pine and found that the yields were 73% (Kappa no: 20), 52% (Kappa no: 20) and 44% (Kappa no: 30), respectively. The high yield might be due to the low lignin and hemicellulose content of hemp bast fibres, most of which are dissolved during cooking. If hemp bast fibres contained a high amount of these substances, the yield would have been naturally lower. Additionally, the high amount of crystalline and highly stable crystalline structure of cellulose in the raw material has a negative impact on the accessibility and swelling of the cellulose fibres, which in turn reduces the rate at which other substances dissolve and the amount of cellulose that is lost during cooking [Gümüşkaya et al. 2007] . As a result, the yield increases. Fibre fibrillation significantly affects the strength of the end product. The properties of cellulosic fibres are greatly optimised by beating or refining to remove primary fibre walls. This allows the fibres to become hydrated before swelling, increasing their flexibility and bonding power [Kumar Agrawal et al., 2015]. According to Danielewicz and Surma- Ś lusarska [2017], the freeness value of pulp exceeded 23°SR after beating for 45 min. Therefore, to determine the mechanical treatment that the pulp had been subjected to, the beating degree was measured repeatedly until the targeted 20 –25°SR was reached (hemp bast fibre pulp consistency: 1.76%). As with their investigation, it took 37 min to achieve the 20°SR. This was due to the highly stable crystalline structure and low hemicellulose content of hemp bast fibre s [Gümüşkaya et al. , 2007]. These properties caused a decrease in swelling capacity, which lowered the external fibrillation of the hemp bast fibres. This phenomenon leads to high energy consumption for beating since it takes too much processing time to reach the desired fibrillation degree. OM analysis The results of 75 measurements of size-reduced raw hemp bast fibres were analysed, and histograms were tabulated in terms of diameter, wall thickness and length. The master thesis of Yaylali [2020] contains the histograms for length,
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