How do you make a pulp tray

Table of Contents

To make a pulp tray, mix one part pulp with four parts water, mold the slurry into shapes, dry using convection or infrared methods, and finish by pressing and coating for durability.

Materials Required for Pulp Tray Production

Making pulp trays involves the use of a wide variety of materials, but the most prevalent one is paper pulp. It is used most often because of its abundance, renewability, and biodegradability. Depending on the intended use of the tray, other materials may be used to provide certain properties. This can include a higher strength, as is the case with sugarcane bagasse, better water resistance, reduced heat transfer or alternates such as bamboo or wheat straw. The two materials of interest here are virgin and recycled pulp, one being both stronger and cleaner than the other.

The usefulness of virgin pulp is related to its nature. This particular material is made from trees directly and not only possesses a high degree of strength but is also relatively high in purity. Trays made from virgin pulp are very commonly used for the packaging of food products. Since the material is clean to handle any impurities or the possibility of contamination is reduced.  Recycled pulp is inferior in both strength and neurological properties. Made from recycled paper, it loses a part of its integrity and can contain other materials, such as ink, used in the production of the original product. For this reason, it is more commonly used for items that are not consumed, like egg trays or packaging for electronic goods.

Many materials need to be used to create good trays, but for them to be considered good in their own right, they need to be both safe and readily available to the company. Sugar cane bagasse is a common material as it generated as a byproduct of sugar production, is biodegradable and thus cheap. Bamboo is also popular as it grows fast and does not require fertilization.


The Pulp Molding Process

The pulp molding process is a procedure that plays a key role in the production of pulp trays. The process implies converting raw materials into a slurry, shaping it to form a specific product, and drying it to obtain a sturdy and lightweight item. The key advantage of the approach is that it is beneficial for the environment and permits the production of biodegradable goods. In this regard, the following techniques of molding used in the pulp molding process need to be discussed in more detail.

Pulp Mixture Procedure

The first procedure involved in the pulp molding process for the production of trays is to prepare the pulp mixture. The raw material used to prepare the pulp slurry is recycled paper or other fibrous materials. The materials should be mixed with water to a specific ratio of the raw materials. The ratio of water to pulp equals one part to four parts, implying four parts of water for one part of cellulose. This is refined and should be broken, meaning the fiber should be disaggregated into small particles and evenly distributed throughout the mixture.

Types of Forming for Trays

There are several techniques of forming a tray shape from the obtained pulp mix. This mix already has a certain percentage of water, but if the portion is too low, it can be added before entering this phase of production. The first technique that can be used to form a tray shape is a vacuum forming technique. This is the most widespread variety when the pulp slurry is placed on top of the mold, and the vacuum sucks out the water, and only the pulp fibers remain at the bottom. The compression molding technique can be used in thicker products . The transfer molding technique may be employed in the pulp molding process of trays in more complex designs.


Drying and Finishing Steps

Once the pulp trays are molded, they require drying and finishing. This process is critical for the trays to be sufficiently dry, strong, and applicable.

Ways for Fast Drying

Drying is essential for the pulp trays as the remaining water must be eliminated for them to maintain their shape. The following are several possible ways:

  • Convection drying: exposing the trays to a high amount of hot air and hence evaporating the remaining water. Most readily used as it is simple and efficient.

  • Infrared drying: employs the radiation from infrared heaters to evaporate the water . It is faster and more effective than convection drying.

  • Microwave drying: vaporing the water in the pulp with the energy of the microwave . It is the fastest method but might be costly.

The drying method for the trays is usually selected by the drying time, the electricity spent, and other requirements to the final product.

Finishing for Strength and Appeal

Once the trays are dried, they should also be processed. The common finishing touches are as follows:

  • Pressing: the dried trays are placed under heated plates and heavily pressed, which reduces the extra portions of the material and densifies the trays, making them denser and stronger and evaporating remaining roughness.

  • Coating:  a layer of the coating can be sprayed into the trays to lessen the permeability to water and increase durability. This is critical for trays to be used for food packaging.

  • Trimming: the leftovers from the molding have a tray with uneven sides. They should be trimmed to enhance productivity.

Thus, the last steps after the molding of the pulp trays are crucial for them to be water-resistant, smooth, and sufficiently dry and dense to be used.

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