Environmentally friendly signs

Saving the world with traffic signs

Sign manufacturers could and should be using more recycled plastic in their products to reduce current unsustainable waste levels

Words | David Valant, Val Plastika, Slovenia

All of Val Plastika’s products, including road signs, are fully recyclable

Road signs are need to provide guidance and safety to increasing traffic. As our traffic network expands, so does the use of raw material, especially plastics.

The need to recycle is increasingly important. Yet figures still show less than 7% of plastic production is being recycled and landfill is by far the most common way of dealing with plastic waste. As industrialists, we need to raise the amount of reused plastic by lowering the cost of recycling and improving the consistency of recycled material.

Traffic signs generally last for decades, so it could be assumed that the contribution to plastic waste from the industry is minimal, but that would be wrong. Traffic sign manufacturers fall into a group that primarily uses new (or virgin) plastic where, in many cases, recycled material would be perfectly adequate. Production of virgin plastics alone represents 4% of annual use of crude oil and another 4% is used for its aftertreatment, transport, etc.

Closed-loop recycling challenges

It is possible to closed-loop recycle most thermoplastics, however plastic packaging frequently uses a wide variety of polymers and other materials such as metals, paper, pigments, inks and adhesives. Industrial packaging is currently recycled to a greater extent than consumer packaging, as it is relatively pure and available from a smaller number of sources of relatively higher volume. The volumes of consumer waste are, however, up to five times greater than generated by commerce and industry, so to achieve high overall recycling rates, consumer as well as industrial waste need to be collected and recycled. In some instances, recovered plastic that is not suitable for recycling back to its original application is used to make a new plastic product displacing all, or a proportion of, the virgin polymer. This can also be considered primary recycling.

Downgrading refers to using recovered plastic in a way not typical for virgin polymer. For example, ‘plastic lumber’ is an alternative to higher-cost/shorter-lifetime timber. This is secondary recycling (ASTM Standard D5033).

Technically feasible but costly

Chemical or feedstock recycling has the advantage of recovering the petrochemical constituents of the polymer, which can then be used to manufacture new plastic or to make other synthetic chemicals. However, while technically feasible, it has generally been found to be uneconomical without significant subsidies because of the low price of petrochemical feedstock compared with the plant and process costs incurred to produce monomers from waste plastic.

At Val Plastika, increasing the amount of recycled material in the production process is important. Some of the company’s in-house consumer plastic waste is closed-loop recycled, however recycling activities are mostly of the secondary variety. This mostly concerns road signs and automotive consumer waste. There are, however, challenges in the process.

Changed beyond recognition

When compared with virgin plastics, recycled plastics tend to have less desirable properties. This includes mechanical and rheological changes caused by permanent chemical and physical changes to the molecular structures and continuous changes in the thermodynamic equilibrium of the molecular structures. The deteriorations in rheological and mechanical properties are attributed to macromolecular chain scissions resulting in a decrease in molecular weight. This occurs when recycling at high temperatures and high shear stresses.

Although introducing additives improves certain desirable properties of recycled materials, it increases the cost. Furthermore, the intricate nature of inter-relative processing parameters might involve repeated detailed experiments that are costly, time-consuming and environmentally unfriendly. The reprocessing of post-consumer plastics involves heating and drying the material, which consumes the thermal stabilizers originally present in the plastics. Recyclates without further treatment are therefore usually less stable to thermal stresses. This problem can be solved by adding new stabilizers, which again adds cost.

An even greater cause of drop in material properties than material degradation is inconsistency of real-life consumer plastic waste. To minimize the effect of inconsistent material, homogenization of recycled polymer in big batches is a feasible solution. For additional improvement, the use of additives is possible. Additives can improve the properties of recycled material to match – or even improve – those of virgin material – but this opens the debate of economic feasibility.

Another challenge we face with recycling is cost: the price of the recycled polymer compared with virgin polymer, and the cost of recycling compared with alternative forms of acceptable disposal. There are additional issues associated with variations in the quantity and quality of supply compared with virgin plastics. Lack of information about the availability of recycled plastics, its quality and suitability for specific applications, can also act as a disincentive to use recycled material. n

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