Challenges in post-consumer and residual materials compounding

Compounding, the key to your success

As we saw in the article on the supply of raw materials, the notion of plastic grade no longer exists with recycled materials. To select the right materials, we must build a charter of materials corresponding to our realities and our needs. This material charter will determine the spectrum of acceptable raw materials and we must limit ourselves to this list of materials if we want to guarantee the success of the company.

However, when you have the ability to compound (mix and improve) plastics, it changes everything.

Indeed, compounding polymers enables us to create your own grades of plastic. We can therefore create our own basic matrices by mixing several different raw materials and we can improve their properties by adding additives.

There are several polymer compounding technologies.

Batch processes, example:

two-roll mill (rubber), internal mixer, thermokinetic.

Continuous processes, example:

Single and twin screws extruders.

However, in the plastics industry the most recommended and most used process is twin-screw extrusion.

The image below shows some compounding processes.

Optimization of the cost/performance ratio of your materials

Compounding is the process through which we can maximize our profit margin because it enables us to optimize both their performances and their costs.

By mixing different polymers, we can successfully combine their properties and some of their strengths.

Certain raw materials that do not comply with our materials charter can thus be mixed with other complementary materials in order to respect our charter. It is even possible that none of the complementary materials respect the material charter but their mixtures does.

Thus, compounding process gives us access to a new world of possibilities:

The one of ''Secondary raw materials ''

Meaning, materials which cannot be used directly but which can still be compounded with other materials to meet expectations.

Thus, compounding offers us much more flexibility in terms of charter of materials and the possibility to buy cheaper raw materials.

The picture below presents a charter of materials with 6 selection criteria. Compounding will give us access to certain secondary raw materials outside the tolerance spectrum (green zone).

Improving the performance of your finished products

Once you have selected and decontaminated the materials that meet your raw materials charter, you will be able to process them. However most of the time you will first have to improve their properties in order to meet the specifications of your finished products.

Indeed, recycled plastics have already a first useful life where they have accumulated contaminants but also suffered degradation. In addition, recycled materials are generally heterogeneous (plastic of the same nature but of different origins).

These peculiarities are all defects that will affect the quality and performance of the finished products. To correct these problems, it will be necessary to compound the material by adding the additives and reinforcements necessary to meet the specifications of the finished products.

We speak among other things about:

• Antioxidants

• Compatibilizers

• Fillers (carbon black, CaCO3, wood powder, etc.)

• Mechanical reinforcements (fiberglass, carbon fiber, graphite, graphene, etc.)

• Cross-linking or vulcanizing agents (rubber)

• Pigments, lubricants, plasticizers…

• Swelling agent, flame retardant…

Some images of these additives below

How to choose the right additives?

There is therefore a multitude of commercial additives to help you meet your specifications.

You still need to choose the right ones because their efficiency is relative and, here again, there is no universal solution.

The efficiency of an additive depends on many factors and can rarely be anticipated:

These include, among others:

• Physicochemical properties

• Nature of the polymer blend

• Production conditions (temperature, mixing speed, residence time, etc.)

• Optimal concentration

Moreover there can be a big difference in price between additives of the same types.

Developing a high-performance compound from recycled materials is very complex and requires expertise.

Manufacturers rely too often on the advice given by their suppliers. Their choice of additives is often dictated by the product cost.

However if some additives cost much more than others, it is obviously for a good reason.

A given additive can be 4 to 5 times more effective than another. In addition, additives often create unwanted or even harmful side effects and interactions. Exceeding certain dosages can be highly detrimental to the performance of your product.

So always choosing the cheapest and adding more if necessary, is not necessarily the best strategy.

The best is to determine which additives are the best match for your needs and goals.

At IPC we work in collaboration with the best additive manufacturers in the world.

We have tested, validated and even helped develop some of the best adjuvants in the field of plastics processing (compatibilizers, antioxidants, crosslinking agents, technical reinforcements, fillers, etc.)

We will be able to help you develop a compound that will meet the specifications of your finished products while maximizing your profit.