What Is a Pulp Machine?

Ray Hawk

A pulp machine is a device that takes waste fibrous material, usually from recycled newsprint or cardboard, and dissolves it in water into a slurry that can then be shaped and dried into new forms such as egg cartons. Pulp molding machines can also process cotton and other textile fibers into useful products as well, though most pulp that is used for containers and packaging materials is sourced from wood waste as of 2011. There are generally two types of pulp machine processing approaches — the oven dry manufacturing method and the thermoformed method.

Recycled paper made with a pulp machine.
Recycled paper made with a pulp machine.

Traditionally, pulp moulding machines have been used to make mostly recycled egg cartons and food containers for large restaurant chains. An increasingly widespread use for the pulp machine, however, is to generate dunnage, or internal packaging that is molded to the object being shipped to cushion it during transport. This is commercially attractive, as the source materials to create dunnage are inexpensive, environmentally-friendly, and the typical pulp machine is versatile enough to create a wide range of three-dimensional pulp product shapes.

Paper egg cartons are made from pulp machines molds.
Paper egg cartons are made from pulp machines molds.

The basic process under which a pulp machine operates is fairly simple. Post-consumer and recycled paper fiber is dissolved in water into a consistent slurry, and a mold is submerged in the water with a screen liner on the surface. A vacuum force pulls the pulp towards the screen, filtering out large fibers and coating the mold with a fine layer of pulp. If the machine is an oven dry design, the mold is then removed from the slurry and the newly-formed pulp shape is detached from the mold and stored on a drying rack under controlled conditions until it is ready for use. The oven dryer method can produce pulp forms with a thickness of 0.06 inches (1.5 millimeters) or thicker, and has a more rapid production cycle than thermoforming, though the end product can often contain distortions.

The thermoforming pulp machine uses a hot press method that shapes and dries the pulp simultaneously. This type of pulp machine is more automated, so labor expense is reduced, but it requires more precision control as well. The thermoforming method is most often used to create finely-molded shapes with smooth surfaces, such as packaging for cellular phones and electronics. It can also produce pulp forms with a thickness range as fine as 0.02 to 0.06 inches (0.5 to 1.5 millimeters).

The industry of molding pulp is unique in that it is naturally environmentally-friendly and energy efficient. The raw materials for making pulp molds would otherwise be disposed of in landfills, and no chemical additives are necessary to use them. Waste water is also not generated in the process, as all water used in pulping is recycled back into the cycle or evaporates. If molds are badly shaped or product runs otherwise don't meet standards, the material can be liquified once again and used for new pulp molds. The oven dryer method also relies on a heated room to dry the pulp products that is often fueled by additional waste wood byproducts such as sawdust.

Egg cartons have been made from pulp machine molds as far back as 1920. Among the new products that a typical pulp machine produces as of 2011 are various types of fruit trays and biodegradable pots for planting flowers or vegetables in a garden, as well as permanent container pots for indoor plants. Many containers that are used in hospital settings are also made from pulp so that they can be disposed of after use instead of needing to be cleaned, and industrial packaging is increasingly made from pulp, such as containers for cushioning light bulbs during shipment.

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