Strike the Right Balance:
How to Maximize Plastic Performance with Fewer Additives
by Yuse Lajiminmuhip

esins such as high-density polyethylene (HDPE) are inherently capable of being manufactured into highly capable products. With minor alterations to the chemical composition of the mixture through additives, manufacturers can enhance the performance of the material in certain areas to meet more stringent project demands. While additives can bring new capabilities to plastic products such as geosynthetics, some additives can migrate out over time, causing the products to lose those benefits. For this reason, manufacturers should consider the qualities of the chosen resin first.

This article describes the purpose of additives in plastics, how the performance of plastic products can be improved through a materials-first policy and ways manufacturers have leveraged the benefits of coextrusion to min-max the benefits of certain additives.

The purpose of additives
Additives in the manufacturing of plastics can help give products new or improved capabilities. Some additives, such as carbon black and antioxidants, are essential in situations where the product is expected to be exposed to sunlight. Carbon black has been used as an additive (also referred to as an absorber of UV) to minimize the impact of ultraviolet radiation (UV) on various products including geosynthetics made with HDPE and polypropylene geotextiles (see figure 1). Even concentrations as low as 2 to 3 percent have been shown to effectively negate the degradation that is typically associated with UV-exposed polyolefins.
AGRU Smooth Liner being used along the inside of a dirt levy
Figure 1: AGRU Smooth Liner is a geomembrane available in black and is made from either high-density polyethylene or linear low-density polyethylene. Smooth Liner is ideal for containment applications as well as landfill caps or closures.
In other cases, products made with resins can lack the physical characteristics necessary for certain constructions. For instance, a customer may want to use polyvinyl chloride (PVC) as a geomembrane for containment. PVC is naturally a very stiff and brittle material. To achieve the required level of flexibility as a geomembrane, the manufacturer will add additives known as plasticizers. While most materials used to make geomembranes will require some additives to stabilize the product and reduce oxidation, some materials such as PVC can require a significant (up to around 25 percent by mass) quantity of additives to achieve the desired results. Why is this a problem?

Some additives, including plasticizers, can migrate out of the product with long-term exposure — eventually causing the product to lose the benefits derived from the additives. Fortunately, installers have many options when it comes to geosynthetics. While PVC may be the material of choice in some applications, it can be better to choose a material that offers innate physical and chemical characteristics that match the desired specifications.

Material first; additives second
While additives are undoubtedly powerful tools to enhance polyolefin performance under various conditions, the variety of available resins makes it possible to create products that are inherently better suited for certain applications. For example, rather than attempt to pigeonhole PVC (a popular piping material) into the geomembrane category, why not consider geomembrane-specialized resins such as linear low-density polyethylene (LLDPE) or HDPE? Such an approach seeks to achieve specification requirements primarily through material performance.

Material-first manufacturing aims to achieve performance through resin selection, with additives serving to augment rather than supplant material qualities (see figure 2). In some applications, it also makes sense to go beyond polyolefins and consider semi-fluorinated and fluorinated polymers. These materials can enable manufacturers to create products with improved chemical and thermal resistance with minimal use of additives, which is especially important for high-purity applications.

Of course, there will be situations where additional capabilities will be required to fulfill project requirements. In these cases, manufacturers can turn to coextrusion.

Combining the best features of coextrusion and additives
Coextrusion is a manufacturing technique that enables the creation of a single product from multiple extruders using different resins. This technique can be leveraged to create unique products that incorporate the benefits from different materials. For example, manufacturers can create a geomembrane that combines a thin layer of expensive additive-infused resin with a thicker portion of standard resin. This approach allows engineers to leverage the benefits of the additive-infused resin at a lower cost.
view of the ARGU material pyramid
Figure 2: The AGRU Material Pyramid helps define cost-effective solutions for specific applications; in this case, semi-finished products that come into contact with a variety of aggressive media.
Conductive geomembrane is another example of a coextruded geosynthetic product (see figure 3). The coextruded geomembrane contains a thin lower layer that conducts an electrical charge. This feature supports a construction quality assurance technique often referred to as spark testing, which helps installers locate holes, punctures, tears, cuts, cracks and similar breaches over the partial or entire area of an installed geomembrane using test method ASTM D7240.
AGRU Conductive Liner mockup
Figure 3: AGRU Conductive Liner is a geomembrane that incorporates a thin coextruded conductive bottom layer that supports construction quality control through ASTM D7240 spark testing.
AGRU-ULTRA GRIP® installed in concrete pipes
Figure 4: AGRU-ULTRA GRIP® installed in concrete pipes offers a way to combine the strength of concrete with all the benefits of a plastic liner.
“Additives have become essential tools in plastics manufacturing to create longer-lasting products with improved performance. The number of available thermoplastic resins with differing properties gives manufacturers options to create products that are specifically suited for a variety of applications.”
Another example of a coextrusion application includes white (or other light-colored) layered geomembranes to help reflect sunlight and minimize the expansion and contraction of the geomembranes, which may produce wrinkles. Structured concrete protective liners with anchors that are embedded into concrete (see figure 4) often use similar coextruded layers with differing colors to enhance damage detection.
To summarize, additives have become essential tools in plastics manufacturing to create longer-lasting products with improved performance. The number of available thermoplastic resins with differing properties gives manufacturers options to create products that are specifically suited for a variety of applications. As a result, it is possible to maximize plastic performance while also limiting the usage of additives, which can potentially migrate out of the product over time. By leveraging a materials-first policy and using techniques such as coextrusion, manufacturers can create highly specialized and performant plastic products.
G. Djamila, R. Nadia, A. Djamel, “Study of the effect of UV aging on the mechanical properties of geotextile based on polypropylene.” AIP Conference Proceedings. (2018). Accessed online March 10, 2021 https://doi.org/10.1063/1.5048179.
A. K. Sahu, K. Sudhakar, R. M. Sarviya, “Influence of U.V. light on the thermal properties of HDPE/Carbon black composites.” Case Studies in Thermal Engineering. Vol. 15 (2019). Accessed online March 10, 2021 https://doi.org/10.1016/j.csite.2019.100534.
T. D. Stark, H. Choi, P. W. Diebel, “Plasticizer Molecular Weight and Plasticizer Retention in PVC Geomembranes.” 57th Canadian Geotechnical Conference. (2005). Accessed online March 10, 2021 https://doi.org/10.1061/40789(168)22.
Yuse Lajiminmuhip is the technical copywriter at AGRU America, Inc. For more information, contact AGRU America, Inc. at 500 Garrison Road, Georgetown, SC 29440-9680 USA; phone (800) 373-2478 or (843) 546-0600, fax (843) 546-0516, salesmkg@agruamerica.com or www.agruamerica.com.