5 Chemical Treatments to Enhance Molded Pulp Properties

Table of Contents

Alkyl Ketene Dimer enhances water resistance, Glyoxal increases wet strength by 50%, and starch-based adhesives improve mechanical strength by 30%.

Alkyl Ketene Dimer (AKD)

Application of AKD in Molded Pulp

  1. Alkyl Ketene Dimer is a chemical derived from fatty acids that makes molded pulp products much more water-resistant, which is critical for a packaging material that is commonly exposed to moisture . The AKD forms a hydrophobic film around the cellulose fibers in the processing of pulp, preventing moisture from getting through. The AKD treatment is especially useful for food packaging, such as egg cartons or fruit trays that should not be re-moisturized for sanitary purposes and ease of storage, shipment, or making the shelf-life of products within them longer and reducing the production of bacteria and mold.

  2. The concentration of AKD in the treatment of pulp varies from 0.5 to 1.5% of the dry weight of pulp . That is typically a sufficient quantity that does not overuse the chemical and allows for the use of the molded pulp in recycling. In a comparative study between AKD-treated and untreated samples, it was found that the former permanently absorbed 40% less water, having been treated with 1% AKD .

  3. Implementing AKD treatment in the manufacture of molded pulp is only typically slightly more expensive, by twenty cents to a dollar each pound, a little less than a 5-percent cost increase . In turn, the product becomes substantialdly higher in quality, reshaping in up to 80% fewer damages during the shipment due to higher fragility of the molded pulp product, and pays off during the transportation then and storage, as the products of the superior packaging will not be wasted.

  4. It does recycle to the same degree as the AKD-untreated molded plup products. Many beverage companies use AKD-treated molded pulp products for their cup carriers that may be exposed to moisture from the condensation of the cups they hold or the beverages they carry.



An example of a cross-linking agent that increases the wet strength of the molded pulp product due to its property is Glyoxal. The idea of such a property is indispensable for products made of molded pulp, which need to maintain a solid form under moist conditions . Glyoxal’s mechanism of action lies in a chemical reaction between the cellulose fibers and the agent, which facilitates the formation of strong bonds between separate fibers . The mold pulp material, the fibers of which have interacted with Glyoxal, demonstrates virtually no solubility in water . This feature is very useful for the products such as, for example, meat trays or plant pots .

Outdoor plant pots made of molded pulp and treated with Glyoxal can maintain their solid structure for several weeks . Despite regular watering, the presence of which is beneficial for plant growth, intact molded pulp is preserved, which is not the case for untreated fiber pulp. An appropriate amount of Glyoxal applied to the molded pulp is also typically effective in terms of the cost . The concentration varies between 0.1% and 0.3% by weight and enhances the wet strength by up to 50% as compared to the untreated material . The manufacturing cost increases by 10%, but due to the long product lifespan, the investment is justified by the reduction of the cost of defective products and the number of complaints from customers. The practical application of the cross-linking agents is primarily in the food industry . Seafood and poultry require wet-resistant packaging materials. Glyoxal-treated packaging ensures that when the packaging gets in contact with the products, their wetness will not cause packaging that is not resistant to moistness to collapse and deform.

Starch-Based Adhesives

Starch-based adhesives help tremendously, as they allow to improve the mechanical strength of molded pulp by adding a natural binder that increases fiber-to-fiber adhesion. As a result, the products become significantly more durable and resistant to mechanical stresses during handling or use. Starch-based adhesives may be used for different products made from molded pulp, although the advantage is probably the most pronounced in packages that must be durable and capable of carrying heavy loads. For example, molded pulp trays used to ship electronic devices are made with a combination of 98% molded pulp and 2% of a starch adhesive mixture. Trays made without any adhesive can collapse under the pressure of 40–50 lbs, but those with a 2% starch mix become 20% stronger and collapse at 60–65 lbs . Therefore, the tray made with the adhesive can be expected to be safer for the transported product.

The adhesive is hardly a significant factor in the price, but it is important to notice that sources of starch currently used in this industry are all natural and biodegradable. The use of this adhesive does not make the product more environmentally hazardous, but the increase in the final price is to be expected. The costs are minimal, making up only about 7% of the total price. However, this effect is rather difficult to measure, as the main companies produce all three elements, each of which can have its separate markup rate . Overall, the influence of the use of starch-based adhesives on the molded pulp products appears to be minimal except for its ability to improve product’s mechanical characteristics.


Polyethylene Glycol (PEG)

Polyethylene Glycol (PEG) is a functional polymer when added to molded pulp, increases flexibility, and reduces brittle character allowing the packaging to accommodate a variety of shapes. Engineered packaging is designed to fit various product geometries to improve protection. PEG maximizes the formation of these dynamic shapes without breakage and loss of integrity.

Molded Pulp’s ideal application is to protect fragile containers such as glassware and electronic devices. The proper amount of PEG is generally 1 to 3%w based on the dry weight of PEG and fiber being used. This addition increases molded pulp elongation at the break by up to 50%, which means that the product can expand and contract without breaking under impact shock. This results in less breakage during both shipping and stocking as molded pulp absorbs rough handling fairly well.

The addition eases processing by providing easier release and reduced wear of the equipment, which will decrease maintenance costs. Economic factors for PEG to be applied to molded pulp products come in two forms, reduction in breakage in shipping and warehousing and increased satisfaction of concealed articles received by use. The cosmetics industry sells in an enormous market with fierce competition. Presentation is one factor of great concern. To protect the valuable product, cosmetic firms ship their product with pulp molded insert trays. The tray holds the product in place, resists tear when the article is pulled out, and in most cases, the pulp’s tear factor is more than sufficient to pull the article from the pulp.

Biocides and Fungicides

Biocides and fungicides are largely used in the production of molded pulp to protect the final product from microbial growth, make the product last longer, and improve food safety. While lime is the main disinfectant, biocides and fungicides serve additional purposes. For example, adding them to the pulp protects fruit trays or seed pots from mold and fungi, which can damage the structure of the product and supply serious health issues. In particular, adding fungicides to the molded pulp prevents young plants in seed pots moistened with water from getting a fungous infection, which can cause the plant to wilt, and prevent this kind of rashes in humans. The concentration of such agents is much lower than that of lime, and they usually do not exceed 0.2 parts of the pulp. However, this is more than enough to reduce the development of fungi by 90% ( vogepulp.com, n.d. ).

Another use of biocides and fungicides in the production of molded pulp is for the food packaging industry. For instance, when the carton or tray is intended for containing egg or vegetables, the use of such treated pulp ensures that these wares do not become a hotbed of bacteria. The effect of adding these chemicals is only up 3% of increasing production costs. While it is possible to generate the same benefits effectively with less damaging options, using these agents is recognised as acceptable. The increase in cost is justified because it allows creating a product that the consumers could trust, and which minimizes the number of returns. For instance, if the molded pulp take-out cover for the restaurant industry gets too moist or too greasy and dissolves during its intended use, customers would avoid using it and be reluctant to return to this place for a new order, which runs against health standards.

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