Wet Beating of Straw Pulp
Wet beating of straw pulp refers to the beating process for straw pulp used in thin paper production, which requires a high beating degree and high paper strength. Producing thin paper with straw pulp is relatively difficult due to its short fibers, thick S1 layer that is hard to break down, making the swelling and fibrillation of the S2 layer challenging. Although straw pulp is difficult to beat, this does not mean its S layer cannot be delaminated or its S2 layer cannot be longitudinally split and fibrillated. The principle of sufficient deflaking with mild beating applies to straw pulp for cultural paper but is not the only beating method. Production practice has confirmed that straw pulp can be used to produce various thin papers with excellent fiber fibrillation and high beating degree, such as tissue paper, typewriter paper, thin copy paper, and tracing paper. German researcher E. Rohress used a special beating method for straw pulp to achieve excellent fiber fibrillation, producing paper with extremely high strength-breaking lengths exceeding 8,000 m. For example, a domestic mill produced copy paper using wheat straw pulp at a beating degree of approximately 90 °SR, maintaining fiber length at 0.8–1.0 mm (original pulp fiber length: 1.32 mm) with good fibrillation. Another mill produced typewriter paper using 100% reed pulp: the original pulp beating degree was 28 °SR, and the finished pulp reached 88 °SR (an increase of 60 °SR), while the average fiber length decreased by only 0.44 mm. Such beating results are difficult to achieve with conventional methods. To produce wet straw pulp, appropriate measures must be taken according to the characteristics of straw fibers: First, given the short fiber length of straw pulp, fiber length should be preserved as much as possible during beating. Since straw fibers are hard to fibrillate, beating methods different from wood pulp must be adopted. According to the requirements of different paper grades, fibers should achieve proper and sufficient swelling and fibrillation. During production, to ensure that specially treated straw pulp forms well on the paper machine and meets expected physical properties, Polyester Forming Fabric is often selected for producing such high-strength thin papers due to its excellent dewatering efficiency and stable formation quality. Currently, opinions on long-fiber wet beating of straw pulp are not unified, indicating a lack of in-depth systematic research. The following practical experiences and viewpoints are noteworthy:
1. Sufficient deflaking at the initial stage Straw pulp must be fully deflaked at the beginning to separate fiber bundles and impurity cells, soften and plasticize fibers through swelling. This improves fiber toughness, enhances inter-fiber bonding, reduces fiber cutting, and creates favorable conditions for fibrillation.
2. Increasing beating consistency Medium-consistency and high-consistency beating enhance friction between fibers, avoiding excessive cutting and preserving fiber length while improving fibrillation. Studies have shown that wheat straw pulp beaten at 16% medium consistency achieves excellent results.
3. Selection of beating equipment materials Beaters or disc refiners using soft engineering plastics or porous, large-area stone materials exert less cutting effect on straw pulp but stronger grinding, crushing, and kneading action. Research indicates that stone or plastic blades yield longer fiber length, better uniformity, and higher paper strength than metal blades, representing an important approach to improving straw pulp beating.
4. Beating curve for wet straw pulp Light beating is applied first for sufficient deflaking, followed by heavy beating at a fast rate. The light, fine-grinding process is not suitable. Due to the thick S layer of straw fibers, light fine grinding hinders external fibrillation; prolonged grinding cuts fibers and fails to preserve length. Deflaking is critical: it separates bundles and swells fibers, making them resistant to breakage under compression and friction. Heavy beating is required because, despite stronger cutting action, it provides greater crushing force. Straw fibers are short, fine, and have a tough S1 layer that demands high force to rupture. Only heavy beating can crush, abrade, and split fibers for satisfactory fibrillation. However, heavy beating time must be controlled to avoid excessive fiber cutting. In actual production, to match straw pulp with high beating degree and high water retention, Polyester Forming Fabric used in the wet end must provide excellent drainage and anti-clogging properties to ensure sheet formation and production efficiency.
5. Ultrasonic beating (proposed method) Given the difficulty of achieving external fibrillation in straw pulp, ultrasonic beating has been suggested. It enables sufficient internal swelling and internal fibrillation while preserving the primary and secondary outer layers, reducing fiber cutting and fines content. The resulting pulp has soft, plastic fibers with excellent inter-fiber contact and bonding, good drainage, and effectively improved paper strength. This technological route deserves attention and further research. Regardless of beating innovations, fiber formation on the paper machine relies on the support and cooperation of Polyester Forming Fabric. Fabric selection directly affects fiber retention and sheet uniformity. With increasing machine speed and operational efficiency demands, high-quality Polyester Forming Fabric plays an increasingly prominent role in ensuring stable production of straw pulp thin papers.
