Elemental chlorine-free delignification of kraft pulp produced from halfa (stipa tenacissima)

Abstract

Halfa, also known as Stipa tenacissima, is grown in North Africa and south Spain. Due to its short fibre length, paper from halfa retains its bulk and takes block letters well. In this study halfa was evaluated for bleached pulp production. Two cellulose pulps with different chemical compositions were pulped by the conventional Kraft process. One from original halfa material and the other from halfa pretreated by diluted acid. The pulp produced from halfa pretreated with diluted acid was bleached by elemental-chlorine-free sequences DEPD and DEDP. The yield, Kappa number, brightness and α-cellulose content of the bleached and unbleached pulps were evaluated. The results show that during the chemical pulping process, the treated halfa cooked more easily than the original halfa. The treated halfa pulp also showed very good bleaching, reaching a brightness level of 94.8% ISO, a yield of 93.6% and α-cellulose content of 96.8% with the DEDP bleaching sequence as compared to an 83.2% ISO brightness level, 92.8% yield and 95.1% α-cellulose content for pulp bleached with the DEPD bleaching sequence. On the other hand, the physicalmechanical properties of the pulp were not notably reduced by the bleaching process. The breaking length, tear and burst index of the paper sheets were acceptable. Therefore, the halfa material could constitute a worthwhile choice for cellulosic fiber supply