Mechanical recycling of PVC waste with flexible PVC extrusion
With its extruders, Bausano participates in the field of mechanical recycling of mixed PVC waste from the construction industry. The circularity of the PVC value chain is a topic of great importance within our company.
PVC circularity is not a priority exclusive to Bausano but also a European priority and one that has no viable alternatives. This leads the entire supply chain to progress toward PVC circularity and to promote products made from recycled materials. Bausano understands the urgency and importance of developing extrusion lines that add value to PVC recovery and circularity.
Recycling and construction are key words that led Bausano to develop an eco-innovative and technically scalable research project on an industrial scale for the mechanical recycling of PVC production waste.
It is worth mentioning that there are mainly two PVC recycling methodologies, mechanical recycling and chemical recycling. Mechanical recycling processes involve separating, grinding and feeding the ground product into the conversion equipment, namely the industrial waste extruder. Chemical recycling, on the other hand, is based on the idea of converting the plastic back into the constituent raw materials for reuse in the synthesis process or other chemical processes. Mechanical recycling is preferred when PVC with known composition and traceability is available. It is currently the most commonly used industry-wide solution and is undergoing continuous improvements both to obtain purer raw materials and new products/uses of the recycled material.
Project objectives and results obtained from flexible PVC extrusion
The recycling process involved mixed rigid/plasticized post-industrial PVC scrap that could not be separated due to containing co-extruded profiles, e.g., gaskets for window and door frames. The end application is to re-extrude the same product or other similar products.
The production process of co-extruding gaskets in flexible PVC extrusion
Rigid/flexible PVC generates large amounts of scrap – e.g., bleed-off due to material or color change, defective profiles – amounting to about 12 percent of production. In the past, this type of waste has never been the focus of any form of recycling but usually destined for landfill, with disposal costs ranging from €2.0-2.5/kg and in some cases even higher. The technological challenge for Bausano, and the plastics sector, has been to recycle such mixed waste, as processing waste consisting of a single type of material, from other production lines such as mono-extruded profiles and molded accessories, was already being recovered and fed back into production, mixed with virgin PVC.
The goal was achieved by developing a mechanical recycling process optimized in relation to the type of scrap to be processed. The aim of this process was to obtain products with performance comparable to those made exclusively from virgin material. This allows these products to be offered on the market, with a highly competitive advantage meaning that they can then be offered on the market with the added value of being produced by a recycling process.
Development of recycled material and identification of possible applications
In the preliminary project activities, the starting materials, namely virgin rigid and flexible PVC compounds used in co-extruded profiles, were analyzed. The main technical issue to be addressed when developing the recycling process is that rigid and flexible PVC have very different rheological profiles and thus very different processing temperatures, so a window of process parameters must be found to ensure effective blending of the two types of material without incurring polymer degradation as a result of high temperatures. In order to develop a recycling compound with homogeneous characteristics suitable for the applications of interest, in terms of performance and aesthetic finish, Bausano pursued the following objectives:
- Optimization of the process of dimensional reduction of the waste
- Mixture formulation optimization, through the addition of appropriate additives
- Optimization of extrusion process parameters to reduce thermal degradation effects, while ensuring optimal blending of the two types of PVC.
A series of compounds were then extruded, with varying compositions, first on a laboratory scale, with our MD30 laboratory extruder, to study feasibility and extrudability.
Subsequently, the formulations and related process parameters that yielded the most promising results were replicated on an industrial scale on our MD Nextmover Twin-screw extruder for regranulation of PVC.
On all the compounds produced, both on the laboratory extruder and on the twin-screw, they were to evaluate the homogeneity of mixing, demonstrate the technical replicability of the recycling process on an industrial scale, define its optimal operating parameters and determine the technical characteristics of the element produced from the new recycling material.
Therefore, some potential applications have been identified for the compound from mixed recycling, possibly with the addition of rigid or flexible virgin material needed to achieve the level of hardness required by the application of interest. Possible applications of the pellets extruded by a post-industrial waste extruder can be pipes, profiles or the initial co-extruded product itself that produced the waste.
For virgin PVC-based applications, the percentage of recycled material used was above 60 percent, which is the lower limit of recycled plastic used to produce products certified as "recycled" by a continuous extrusion process. It should be noted that this percentage represented a target particularly ambitious from a technical point of view, given the heterogeneity of the characteristics of PVC waste.
In the final phase of the project, each of the identified components were physically made with the developed recycling compounds in order to compare their performance with similar specimens made from virgin material.
Co-extruded gasket in flexible PVC extrusion
For the production of the rigid part of the co-extruded gasket, according to the defined hardness target (ShD), the compounds used are from recyclates with added virgin rigid PVC.
The gasket produced under the optimum conditions, in terms of extrusion parameters and starting compound, meets the minimum requirements for hardness and dimensional stability to fit properly into the intended housing for the final application (these are gaskets for gates).
The surface finish is comparable to that of the same component produced from virgin PVC.
Single-extruded rod in flexible PVC extrusion
For the manufacture of this component, according to the target defined hardness, up to 80 ShA, the recycled compounds with added flexible rigid PVC were used. The rod produced under the optimum conditions, in terms of extrusion parameters and starting compound, meets the minimum requirements for hardness and dimensional stability to fit properly into the intended housing for the final application, and performs even better than the corresponding virgin material due to the slightly higher average hardness obtained.
The performance required from the tubular component is such that it should not leak out of its housing as a result of a pulling stress, either caused by tensioning the sheet or by wind.
This eventuality is due to both the deformability of the constituent material and the geometry of the component, as it is a hollow profile. A specially designed test was carried out in this case that exactly simulates the described stress. The aesthetic performance is indistinguishable from that of the extruded tubular component with virgin flexible PVC.
Conclusions and future developments
The closed-loop PVC recycling process developed by Bausano has principally generated concrete research and development data that can be applied to our customers. In turn, they will benefit from many advantages if they adopt recycling with a Bausano Extruder, even in this historical time of raw material shortage. These advantages are as follows:
- A lower environmental impact, thanks to a drastic reduction in production waste sent to landfills and the use of virgin raw materials from non-renewable fossil resources, partially replaced with secondary raw material;
- Significant economic savings, to the extent that the company will see an immediate reduction in both the expense item related to its production waste disposal operations previously and the cost and difficulty of purchasing raw material;
- The possibility of applying our energy-saving systems to a PVC recycling process through induction heating of the cylinder, allowing further cost savings and environmental protection;
- The possibility of monitoring all production parameters through our Industry 4.0 Orquestra IoT system.
The use of PVC from recycling, with or without the addition of virgin PVC, for new productions different from those currently in place, may be evaluated as a further future development in order to expand the range of products offered by Bausano.