For years we were left almost in the dark wondering what was going to be the best solution to the problem of waste disposal for post-consumer diapers (or commonly called “soiled” diapers). The proven technologies so far have always been the use of direct incineration for energy recovery (popular in Europe) or converting soiled diapers into RDF (refuse derived fuel) to generate heat in industrial applications. Amazingly to most people, incinerating diapers is already a better solution for the environment than using biodegradable diapers that end up being thrown to an anaerobic landfill, especially if this landfill is not equipped with methane gas recovery systems or using cloth reusable diapers, when they are not dried by the sun (as compared to using a centrifuge and an electric dryer).

A few technologies that recycle diapers have been tried such as Knowaste, TerraCycle and a few others, but these technologies were never economically sustainable by themselves or able to manage large enough volumes to justify their immediate cloning to multiple locations worldwide. Even though some of these technologies have been promoted for decades now, investors keep questioning their business models. The road has not been easy to say the least, but I do hope they keep trying.

The fact is that most diapers continue to end up in the landfills despite growing consumer concerns about the environment. It is clear millennial parents are becoming less patient with our solutions to reduce the environmental impact of diapers. The truth is that diaper incineration does not have a positive perception from consumers due to the conversion of diapers into carbon dioxide, a greenhouse gas. Unless a new technology is developed to lock-in the CO2 into the ground (some companies are working in this direction), incineration is not going to be a great solution, for sure I do not see it becoming the ideal anytime soon.

Luckily for our industry, everything changed about two and a half years ago when two companies started to leak information about the projects they were working on. Later they used those same projects in their social media platforms to inform the world that a solution for post-consumer diaper recycling is not far away into the future. They are currently traveling the world presenting papers to key influencers and also at diaper industry conferences worldwide. The best-known prototype factories for post consumer diaper recycling are those operated by P&G-Fater in Treviso, Italy, a process using a rotating autoclave and raw material separation with a mesh (there are several YouTube videos about this factory if you are interested in watching them); and the post-consumer project using the biomass in the soiled diapers for hydrogen generation, and ozone bleaching to recycle the pulp, proposed by Unicharm. Other companies are also promoting their own recycling efforts, although less aggressively. These include Kimberly-Clark with its joint work with Envirocorp in New Zealand and Essity through its collaboration with Renewi in Europe. All of these projects are currently racing against the clock to try to demonstrate to the world that they will end up with the best and most economic solution or the most ecological solution. They all want to be the first to claim this milestone.

Regardless of how exciting these projects may be, there is one particular conflict that few people have mentioned. For a typical diaper recycling process to work, it needs to separate all plastic components, like polyethylene and polypropylene into pellets that can be used later in other industries, such as plastic injection, to mention an example. For that to work in the most efficient way, they need to feed the machine with only synthetic products, anything else could be detrimental to the quality of the pellets, or an additional separation process needs to be added.

Unfortunately things are not so simple. In today’s market, a group of consumers is emerging that prefer to avoid the use of synthetic materials near babies’ skin favoring instead natural alternatives. These consumers want diapers that use plant-based components, such as starch-based films, PLA, different kinds of viscose (from bamboo, pine or eucalyptus) and the use of biodegradable SAPs. Adding hydrophobic cotton into the mix with the nonwoven used for the topsheet or in the backsheet is not really a big problem with regards to recycling because the cotton can be extracted and combined with the cellulose as a single output. However, mixing natural films or plant-based plastics with the synthetics may contaminate the resulting plastics or can make the recycling process more complex. The problem is that we will need to separate plant-based products from those made with synthetic components for the post-consumer recycling process to work efficiently. This brings a new question— how will we structure the collection stream of soiled diapers so as to avoid mixing different types?

A well-known solution for managing post-consumer plant-based diapers is to compost them. Unfortunately, this process cannot be carried out by the consumer from their home in a composting facility installed in their own garden, as most plant-based materials like PLA or other plant-based plastics used in diaper construction require at least 60 C for them to start to decompose to transform into compost, and this is out of the scope of a small composting installation. In addition, you need to pump air to avoid the generation of methane gas, a gas that is dozens of times worse for the environment than CO2. The correct approach for this stream of diapers should be the use of an industrial composting facility. This process should be managed as an aerobic composting solution. This is a process where plant-based diapers are mixed with other biodegradable materials and allowed to compost in an industrial factory at temperatures higher than 60 C under the presence of constant available air. Using a filter at the end of the composting cycle process to remove any minor components that do not compost such as elastics, hot melts, and a few other things may not be hard, and they could be small in volume when compared to the resulting compost. The SAP can be recovered and used in the final compost as long as a bio SAP material is used or a potassium based synthetic polyacrylate (similar to the original SAPs that were sold in the mid 1980s) is used instead of the sodium polyacrylate alternative. I am not sure if it is conclusive that the Na-SAP can be beneficial to the soil in the long term if its ratio of usage is low enough in order to avoid increasing the salinity of the soil; in any case, and just to be extra safe with its agricultural usage, I believe it is better to replace it with K-SAP to avoid a salinity level that may kill the plants using the composted soil. I believe finding a biodegradable SAP (like the new raw materials currently being developed by companies like Thetis or Ecovia), or a good synthetic K-SAP substitute, one that is compatible with agriculture, should not be as hard as the complexities of the diaper recycling alternative. I also believe that any recycling process that requires an autoclave that is working with “batches” will never be as efficient as one running continuously.

We have the same problem for the plant-based diapers as we have for the synthetics. If a diaper was made with all synthetic components and mixed with the input blend to the compost, it will never be able to compost and could even contaminate the composting process. At the very least we need the laminated backsheet to be compostable so that it can break apart and expose the soiled organic components inside the diaper to compost.

In conclusion, I believe our industry needs to develop these two conflicting roads so that more options can be offered to consumers, whether they prefer to use recyclable synthetics or to use natural plant-based components. Both alternatives need to have a good end of life solution. Another critical issue is that they share the same bottleneck: a need for an efficient collection stream so that soiled diapers can be either recycled or industrially composted accordingly.

I have suggested at the diaper workshop during the recent Hygienix Conference, the use of a special garbage bag that can be thrown into the garbage truck and will not explode or break apart while the garbage is being compacted inside the truck, like a bag that is breathable only while under pressure, or a bag with a special check valve. This way we may be able to avoid a special stream and do the separation at the sorting facility in a centralized location, reducing complexity to consumers and cost. A simple proposition is to use one color garbage bags for synthetics and another for plant-based diapers, both using an RDIF sticker so they can be identified automatically at the sorting center.