The global food supply chain has developed to the point where a wider variety of goods have become available to the public than ever before. For example, it is now commonplace to see fruits, vegetables, and meat sourced from across the globe line the shelves of supermarkets. Specialized packaging is one of the reasons for this.
An example of such packaging is coated corrugated cardboard, traditionally prepared with a wax barrier applied via curtain or spray coating techniques. This barrier coating prevents the intrusion of water or oil that can soften the cardboard’s material, causing the package to collapse. Cardboard coating formulations typically use paraffin wax as the predominant ingredient for this application. However, paraffin wax alone is insufficient to provide the required robustness the coating needs for the packaging. Specialty polymers like Westlake’s EPOLENE® are necessary to create cardboard coatings with excellent durability that maximize the packaging’s ability to protect goods traveling across the globe.
EPOLENE® Polymers
Westlake’s EPOLENE® products are low- and medium-density polyethylene polymers domestically produced using a vertically integrated process in Longview, Texas. Often used in applications as modifiers for waxes, EPOLENE® polymers are highly pure and possess melting points and hardness properties typically greater than those of most natural and synthetic waxes. EPOLENE® polymers easily disperse in mixers, facilitating ease of use when preparing wax blends.
Why is EPOLENE® used in cardboard coatings?
Specific EPOLENE® grades with highly branched polymer structures, known as EPOLENE® C-grades or coating grades, are developed for barrier coating applications. When small amounts of these polymers are blended with paraffin waxes used in cardboard coating applications, the strength, adhesion, and barrier performance are improved, as detailed below.
Reduced coating brittleness and increased toughness
Paraffin wax is typically produced as a byproduct of refining petroleum, making it relatively inexpensive to use as a base ingredient in wax-based coatings. However, it tends to be quite brittle, so it is naturally inconducive to forming coatings with high durability. Adding branched EPOLENE® C-grades helps enhance physical properties such as hardness, tensile strength, and elongation. This allows coatings to be more durable under the stress that the packaging may endure while in transit, leading to fewer compromises in cardboard structure.
EPOLENE® C-grade polymers are believed to increase the physical properties of paraffin wax due to their ability to control the uniformity and balance between the amorphous and crystalline areas. Below are images of paraffin wax with varying amounts of EPOLENE® C-15, where increasing the EPOLENE® content also increases the size and spatial uniformity of amorphous and crystalline regions.
Control – 0% EPOLENE®
0.5% EPOLENE®
1.0% EPOLENE®
3.0% EPOLENE®
Higher adhesion to fibrous surfaces
Nowadays, nearly half of all recycled paper is used to manufacture paperboard, which constitutes corrugated box packaging. The recycling process inevitably shortens the length of cellulose fibers in paper, making it more difficult for coatings to adhere to the surface. Westlake has developed maleic anhydride–grafted polyethylene, or Ma-PE EPOLENE® C-grade polymers. When blended with paraffin wax in as little as 2%, they greatly enhance the adhesion to fibrous surfaces. The adhesion increase is thought to originate from favorable interactions between the maleic anhydride groups on the polyethylene polymer and the hydroxyl groups on cellulose, as depicted below.
Enhanced oil and water barrier properties
As described previously, one of the main functionalities of cardboard coatings for packaging is to prevent the collapse of the cardboard by functioning as a barrier to water and oil. EPOLENE® C-grades are based on polyethylene polymers that are naturally hydrophobic and resistant to oil. Thus, both oil and water resistance increase when added to paraffin wax blends. The mechanism by which EPOLENE® increases the uniformity and balance of paraffin wax blends also helps create a more even coating surface, which reduces defects and the possibility of coating gaps forming on the surface. This leads to less intrusion of oil and water by providing a more consistent barrier. In addition to the functional improvements made to these coatings, EPOLENE® C-grades also increase gloss and enhance the appearance of the packaging surface.
Recommended EPOLENE® Grades for Cardboard Coatings
Westlake’s EPOLENE® polymers are designed to improve the physical properties of paraffin wax blends used to create cardboard coatings for packaging. Such coatings using EPOLENE® polymers increase the durability and longevity of packaging. EPOLENE® coating grades and maleic anhydride coating grades are designed to improve the physical properties of cardboard coatings, such as hardness, tensile strength, and elongation. EPOLENE® polymers also increase the adhesion of wax-based cardboard coatings onto fibrous surfaces and enhance the gloss and visual appeal of packaging. Click below to discuss your application and request a sample of EPOLENE® today.
