Why The Silva Cell Isn’t Made of Recycled Plastic

“Is it recycled?”

This is a question that we hear all the time.  While most of our other products are made of a minimum 50% post-consumer material, currently the Silva Cell is not able to incorporate recycled plastics (the steel tubes in the decks are 50% recycled). There are many reasons for this. Our fervent hope is that over time we will be able to significantly increase the use of recycled materials in this product, but in the meantime, I wanted to share a bit about the reasoning behind this decision.

Currently the Silva Cell is made of a very specific compound resin which is a blend of polypropylene and glass. This combination has strength and other important characteristics which make it ideal for the ultra-urban environments where the Silva Cell is used. It is such a specific blend that we have only qualified a very small number of vendors who have adequately rigorous standards and can provide the testing and sophistication to supply us these materials.

As materials are recycled they lose certain structural components and characteristics, and this loss of structural integrity creates a predicament for a product like ours. The Silva Cell is quite unlike a plastic bag, or some impossible to open clamshell packaging that is used once and discarded. In contrast, the Cell is used every day for decades; longevity is a key reason why we settled on this compound blend. Unfortunately, the use of recycled plastic would compromise the structural integrity of the product, and therefore the entire approach to creating long lasting green infrastructure in the built environment. It would also require a number of ecological, engineering and economic compromises, including:

More plastic.
More recycled plastic would be needed in order to achieve the same strength characteristics as non-recycled plastic, making the product significantly thicker.

Greater energy usage.
Using greater amounts of recycled material would require significantly higher energy costs.

Higher shipping costs.
A heavier product (due to the inclusion of more recycled plastic) would be more costly to purchase and ship.

We chose our specific compound and mix after testing and rejecting numerous other materials. The Silva Cell was developed using a dual program of Finite Element Analysis (FEA) computer modeling and physical load testing. Using this approach, the FEA was used to predict the overall strength and response to loading and the physical load testing was used to prove the strength and response. Throughout the entire process, the final end-use was kept at the forefront of the design: to create a system that can handle H-20 loading while also facilitating the growth of healthy trees in sites such as parking lots, sidewalks, plazas and more.

We have taken a very conservative approach in the development of our engineering standards and resulting safety factors. Our feeling is that we’re creating a tool for the long term and it is critical that we meet both engineering needs and the ecological requirements of integrating trees and stormwater.

The product development process is a never ending series of compromises between costs, function, and market realties. The Silva Cell is just the first generation of these tools that we are developing. Our goal is to create green infrastructure that can complement, and in some cases replace, the gray infrastructure that has dominated of decades.  As a company it is our responsibility to consider the competing needs of sustainability, engineering practicalities, and cost — a very difficult balance to achieve.

While we can’t release any details just yet, we are hard at work to create the next generation of products which will further advance our green infrastructure goals. We look forward to advancing the science and understanding behind our products and bringing green infrastructure to a much greater audience.

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