Crop Stalk Pulp Making

Crop stalk is a general term for the stems and leaves (ears) of mature crops. Usually refers to the remainder of wheat, rice, corn, potato, canola, cotton, sugar cane and other crops (usually coarse grains) after harvesting the seeds. More than half of the photosynthesis products are found in straw, which is rich in nitrogen, phosphorus, potassium, calcium, magnesium and organic matter. It is a multi-purpose renewable biological resource.

As the by-product of crops, the main treatment is incineration. Straw burning was once regarded as the main cause of air pollution, which also caused serious waste of resources. The utilization rate of straw resources is greatly reduced. It can be seen that the reuse of crop stalk is an important way to reduce environmental pollution and improve the utilization of straw resources. Among all uses of crop stalk, pulp of crop stalk is typical and cost-effective.

Demand of crop stalk pulp

China has abundant agricultural resources, and the proportion of straw is large. In China’s paper and pulp industry, the shortage of raw materials for paper making is always a problem, as the main raw material for papermaking. China’s wood fiber resources are relatively scarce and need to rely on imported wood pulp. The shortage of fiber materials limits the development of China’s paper industry. Therefore, choosing a suitable papermaking raw material to replace wood raw materials is a major research topic in the paper industry. There are some common non-wood fiber materials like wheat straw, bamboo, sugarcane bagasse, cotton, jute and waste paper, etc.

Pulp of crop stalk

The new biodegradable pulping technology uses agricultural waste such as straw, corn stalk, wheat straw and cotton stalk as raw materials, and uses various specific microorganisms as inoculants, through engineering treatment and biological fermentation process, decompose and oxidize lignin, hemicellulose, etc. and the cellulose therein is separated and applied in the paper industry.

Currently some paper pulp mill has successfully explored the use of straw, and achieved the “one grass and two uses”, and solved the problem of straw burning by the market. The so-called “one grass and two uses”, one is to use straw to make paper, the key index of the straw pulp is better than the hardwood pulp, and change the situation that the straw pulp can only be used for low-grade products such as cardboard paper.  The straw pulp also can be used to produce cultural paper, household paper, etc. The second is to refine the main pollutants in the papermaking process to produce fulvic acid organic fertilizer, which has been applied in 40 million mu of cultivated land in China. According to estimates, a new-type pulp plant that processes 1 million tons of straw per year can save the straw on 4 million mu of cultivated land from incineration.

Crop stalk include the stalk of wheat, rice, corn, potato, canola, cotton, sugar cane, and etc. corn stalk is a typical fiber materials for paper making. How to make pulp from corn stalk?

Corn stalk pulp

The corn stalk is composed of skin, stalk and leaf in a certain proportion. The Table 1 shows that the total amount of stalks and leaves is more than 60%, and the amount of skin is less. The amount of ingredients contained in each part is different. As shown in Table 2, the stalk contains more lignin than skin. The large amount of lignin can lead to reduction of fiber strength and yellow color of pulp, which will affect the mechanical properties and whiteness of the paper. The protein, fat, starch, sugar and the like are higher in the stalk, and the obtained pulp is not ideal and relatively viscous. The crop stalk contains small amount of lignin and high specific content of cellulose, which is not much different from the cellulose content of wood. So that corn stalk can be used as a good raw material for papermaking.

Part Leaf Skin Stalk
Quality Fraction(%) 49-53 30-35 15-16

table1

component concentration lignin cellulose ash
skin 16.15 67.22 0.46
stalk 23.07 71.43 0.46

table2

Due to the difference in the chemical composition of the skin and the stalk, we separated the skin from the stalk and make paper. Table 3 compares the chemical composition of corn stalk and other crop by-products. According to the data, it can be concluded that corn stalk can be used as a great fiber material for papermaking. But the straw skin is smooth and tough, block the extraction of fibers. This layer contains substances such as hemicellulose, pectin, water-soluble matter, paper wax and etc. To disperse the fibers, it is necessary to pretreat to remove this layer of material.

materials Moisture (%) Ash (%) Cellulose (%) Pentosane

(%)

Lignin (%)
Corn stalk 9.6 2.97 44.69 20.58 16.56
reed 14.13 2.96 43.55 22.46 25.40
Wheat straw 10.65 6.04 40.40 25.56 22.34
Sorghum stalk 9.43 4.76 39.70 24.40 22.52
Rice straw 9.87 15.5 36.20 18.06 14.05

table3

According to the above analysis, the suitable method for corn straw papermaking is to pretreat the corn skin, use pulp digester to extract the fiber by pulp cooking, bleach the pulp to meet the requirements of whiteness, and refine the fiber by beating. Through this series of processes, the qualified paper can be produced.

Non-wood fiber papermaking is gradually becoming a major trend. Applying corn stalks to the paper industry not only can alleviate the shortage of resources, but also make full use of straw resources, greatly reduce the pollution of straw burning.

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