Evaluating the performance of hemp bast fibres in the production of packaging paper using different …
When paper made entirely from wastepaper (0% hemp) was compared with paper made with 100% hemp, the increases in paper indexes were as follows: 27.8% for CMT, 26% for CCT, 27.2% for RCT, 23.5% for stiffness and 6.2% for SCT. These increases are not significant because it was expected that blending with hemp bast fibres would considerably increase the compression strength values of the paper. Numerous analyses have shown that the main cause of this low increase is a fibrillation issue with the hemp bast fibres. The tear resistance index normally increases as the hemp bast fibre ratio in the paper increases [Yaylali 2020]. Danielewicz and Surma- Ś lusarska [2017] suggested the same phenomenon with this study on adding hemp bast fibre pulp in small amounts to pulp with low tear strength, such as wastepaper pulp, to improve this property. The increase for paper made from 100% hemp compared to that of 0% hemp was 10.8% and 15.4% in the cases of paper made from 40% and 60% hemp, respectively. In contrast, the paper made of 80% hemp had a 24.6% higher tear resistance index than paper made of 0% hemp. This low and imbalanced increase in tear resistance index could be due to the low external fibrillation of the hemp bast fibres after beating. Numerous authors have noted that the hemicellulose content and consequently the degree of external fibrillation of fibres increase the tensile strength of paper [Gümüşkaya et al. 2007; Danielewicz and Surma- Ś lusarska 2017]. During pulping and mechanical refining, hemicelluloses are absorbed into fibre surfaces, where they may facilitate inter-fibre bonding. Owing to their non-crystalline hydrophilic nature, they may also contribute to pulp swelling and facilitate sheet formation [Kalia et al. 2011; Kumar Agrawal et al. 2015]. Hemp bast fibres exhibit low external fibrillation due to their highly stable crystalline structure and low hemicellulose content, which aids swelling. In this study, these results are consistent with the drawbacks of hemp bast fibres. Breaking length and stretch indexes decrease generally with an increase in the hemp bast fibre ratio of the paper [Yaylali 2020]. The decrease in breaking length and stretch index of paper was 19.6% and 24%, respectively, for the 100%-hemp and 0%-hemp papers. With an increase in hemp bast fibre ratio, the ‘ low degree of external fibrillation of hemp fibres ’ phenomenon also generally causes a decline in the bursting strength index of paper [Yaylali 2020]. In the case of the 100% hemp sample (compared to the 0% hemp sample), there was a 22.6% fall in the paper bursting strength index. This was due to the inter-fibre bonding decreasing as the hemp bast fibre ratio increased. The air resistance index (passage time of 100 ml in air through the paper per g/m 2 ) generally decreases as the ratio of hemp bast fibres in the paper increases [Yaylali 2020]. Compared to the 0% hemp, the decrease in the air resistance index of the paper was 68.9% for the 100% hemp sample. Since hemp bast fibre pulps have low specific gravity and high bulk with open and looser fibre structures, papers made from hemp bast fibres have high air permeability and low air resistance [Ashok Kumar et al. 2017; Dutt et al. 2009]. In addition, wastepaper contains fines that are higher than those in refined
Made with FlippingBook Annual report maker