Raw Materials for the Dry-Press Pulp Molding Process: The Dominant Role of Recycled Corrugated Cardboard

In the dry-press pulp molding process—widely used to produce industrial packaging, egg trays, fruit trays, and electronic liners—the selection of raw materials directly affects product quality, production efficiency, and environmental footprint. While various fibers exist, the dominant and most practical raw material is recycled corrugated cardboard.

Primary Raw Material: Recycled Corrugated Cardboard (Old Corrugated Containers, OCC)

The dry-press process relies almost exclusively on recycled corrugated cardboard as its fiber source. This material is typically derived from post-consumer or post-industrial corrugated boxes, often referred to as OCC (Old Corrugated Containers).

Why recycled corrugated cardboard is preferred:

1. Fiber properties – Corrugated cardboard contains relatively long cellulose fibers that provide adequate strength and flexibility for molded products. These fibers allow the formed products to hold their shape during drying and handling.

2. Low cost – Compared to virgin wood pulp or agricultural residues, recycled corrugated cardboard is abundantly available and inexpensive, making it the most economical choice for high-volume production.

3. Wide availability – Corrugated packaging is ubiquitous in supply chains worldwide, ensuring a stable and continuous supply of raw material for pulp molding facilities.

4. Excellent recyclability – The dry-press process itself is part of a circular economy: used boxes are repulped, molded into new products (e.g., egg trays), and those products can be recycled again after use.

How Recycled Corrugated Cardboard is Prepared for Dry-Press Molding

The typical preparation sequence is straightforward:

1. Sorting and cleaning – Corrugated cardboard is separated from contaminants such as tape, staples, plastics, and adhesives.

2. Pulping – The cardboard is mechanically mixed with water to break it down into a fibrous slurry. No aggressive chemicals are required.

3. Refining – The slurry is moderately refined to achieve a suitable fiber length and consistency. Over-refining is avoided because the dry-press process does not require extremely fine fibers.

4. Forming – The pulp is vacuum-formed on a mold, then mechanically pressed to remove water. The "dry-press" name refers to the fact that less water is used compared to wet-press processes, and drying energy is reduced.

Additives (Minor Components)

While recycled corrugated cardboard is the main raw material, small amounts of additives may be introduced to enhance specific properties:

• Water repellents (e.g., wax emulsions or AKD) – for moisture resistance in humid environments.

• Strengthening agents (e.g., starch) – to compensate for any fiber degradation after multiple recycling cycles.

• Colorants – when colored packaging is required.

However, in standard dry-press products such as egg trays or industrial liners, additives are often minimal or absent, relying instead on the natural properties of recycled corrugated fibers.

What is NOT typically used as the main raw material?

To avoid confusion, it is important to note what does not serve as the primary raw material in dry-press pulp molding:

• Virgin wood pulp – too expensive for commodity dry-press products.

• Agricultural residues (straw, bagasse, bamboo) – more common in wet-press or specialty molding; not cost-effective or process-optimized for dry-press.

• Mixed office paper or newspaper – these have shorter fibers and lower strength, making them unsuitable as the primary component.

Conclusion

In summary, the dry-press pulp molding process is fundamentally built on recycled corrugated cardboard (OCC). This material offers the optimal balance of fiber strength, low cost, widespread availability, and environmental sustainability. By using recycled corrugated cardboard as the direct raw material, the dry-press process exemplifies a practical, circular economy solution for converting waste packaging into valuable new products.