Carbon fibre is as thin as a strand of human hair but is five times stronger than, twice stiffer and lighter than steel; thus, an ideal advanced material in aerospace and automotive industries. However, carbon fibre is 20 times more expensive than steel because of expensive precursors, polyacrylonitrile and pitch, that account for 51% of the total manufacturing cost. Therefore, an alternative precursor, with superior properties, is required. Although successful studies for lignin extraction in subcritical phenol have been reported, there are no studies on evaluation of the lignin fundamental properties related to its suitability as a precursor for carbon fibre. In this study, the extraction of lignin from biomass was conducted in a batch system under subcritical phenol conditions by focusing on its fundamental properties (average molecular weight and glass transition temperature). The effect of temperatures (260–300 °C), reaction times (1–30 min) and solids loading (6 and 10 g) on these properties was determined. The results indicated that lignin from biomass under subcritical phenol conditions fulfilled the requirement as a precursor for carbon fibre. The average molecular weight and glass transition temperature was in the range of 145.5–269.6 g/mol and 40.5–89.3 °C for lignin from empty fruit bunch. On the other hand, the average molecular weight and glass transition temperature of lignin from oil palm frond was 263.8–435.4 g/mol and 71.2–96.3 °C. The increase in temperature reduced the dielectric constant of the subcritical phenol and facilitated lignin depolymerisation. The reactive fragments and the active sites were capped by phenol to suppress the cross-linking reactions and hence the formation of heavier fragments. The minimal decrease in average molecular weight and glass transition temperature of lignin with solids loading supported the conclusion that repolymerisation of lignin likely did not occur under subcritical phenol conditions.

碳纤维像一根头发一样细，但强度却比钢强五倍，刚度和重量轻两倍。因此，是航空航天和汽车工业中理想的先进材料。然而，由于昂贵的前体，聚丙烯腈和沥青，碳纤维的价格是钢的20倍，占总制造成本的51％。因此，需要具有优异性能的替代前体。尽管已经报道了在亚临界苯酚中提取木质素的成功研究，但尚没有有关评估木质素作为碳纤维前体适用性的基本性能评估的研究。在这个研究中，从生物质中提取木质素是在批处理系统中，在亚临界酚条件下，着眼于其基本特性（平均分子量和玻璃化转变温度）。确定了温度（260–300°C），反应时间（1–30分钟）和固体含量（6和10 g）对这些性质的影响。结果表明，在亚临界苯酚条件下，来自生物质的木质素可以满足作为碳纤维前体的要求。空果串中木质素的平均分子量和玻璃化转变温度为145.5–269.6 g / mol和40.5–89.3°C。另一方面，来自油棕叶的木质素的平均分子量和玻璃化转变温度为263.8–435.4 g / mol和71.2–96.3°C。温度的升高降低了亚临界酚的介电常数并促进了木质素的解聚。反应性片段和活性位点被酚封端以抑制交联反应，从而抑制了较重片段的形成。木质素的平均分子量和玻璃化转变温度随固体负载的最小降低支持了以下结论：木质素的再聚合在亚临界酚条件下可能不会发生。