For vascular plant [18], different organs are all composed of vascular tissue embedded in parenchyma tissue and epidermis tissue cover. For vascular tissue, the wall of vessel cell and fiber cell wall (bundle sheath cell) is rich in lignin because secondary wall is lignified. While for parenchyma tissue, parenchyma cell wall is rich in cellulose because there is only primary cell wall.

4.2.1 Tissue Level

According to Sachs’ convenient classification [18], the body of a vascular plant is composed of three tissue systems, the dermal, the vascular, and the fundamental (or ground). The dermal tissue system comprises the epidermis and the periderm. The vascular tissue system contains two kinds of conducting tissues, the phloem (food conduction) and the xylem (water conduction). The fundamental tissue system (or ground tissue system) includes parenchyma tissue, secretory tissue, collenchymas tissue, and sclerenchyma tissue.

There is cutin layer out of the dermal tissue system [19]. Cutin layer is composed of cutin and wax. Cutin is mostly polymers composed of C16 and C18 monomer. Parenchyma cell under dermal is hardened, leading to high lignin content. For vas­cular tissue system, vessel cell in xylem is thickened so that lignin content is high too. There are mainly parenchyma tissue cell in ground tissue system. For parenchyma tissue cell, there is only primary cell wall which is composed of cellulose. In terms of mass content, vascular plant is mainly composed of ground tissue system and vascular tissue system. Therefore, vascular plant could be simply fractioned into vascular tis­sue fraction which is rich in lignin and ground tissue fraction which is rich in cellulose.

Corn stalk could be fractionated into vascular tissue fraction and parenchyma tissue fraction manually. Vascular tissue fraction includes fiber cell around vascular because fiber cell is connected tightly to xylem and phloem, and both fractions are hydrolyzed with enzyme for 48 h. It is found that glucose content from parenchyma tissue is higher than that from vascular tissue by 22.5 %. Corn stalk could be frac­tionated into vascular tissue fraction and parenchyma tissue fraction with steam explosion integrated mechanical carding. For rind and leaf, the enzyme hydrolysis rates of parenchyma tissue fraction are 1.77 and 1.37 times higher than vascular tissue fraction, respectively.

Vascular tissue fraction from corn stalk is tested by pulping with ethanol self cat­alyzing. It reveals that pulp yield could reach to 57.6 % while pulp whiteness reached

65.9 % when catalyzing time is 2.0 h at 160 °C with ethanol concentration 50 % and solid-to-liquid ratio 1:10. The whiteness meets the requirement of printing paper [20].

Corn stalk has not been applied in pulping in that there is much non-fiber cell. Non-fiber cells are mainly parenchyma cell and dermal cell, and the fiber cell content in corn stalk is low. Moreover, the ratio of length to width for corn stalk fiber cell is smaller than other pulping materials. Therefore, if the whole corn stalk is applied for pulping, pulp yield is low and the quality of paper could hardly meet the requirement. If non-fiber cell could be removed and fiber cell content is high, corn stalk would become another resource for pulping.