In the field of Research & Development projects, Nuova Pasquini e Bini S.p.A, after the realisation of GEA pots with materials derived from renewable and compostable resources, counts another collaboration for the study of new bio-composites that can be used for the moulding of horticultural pots.
On 10 February 2022, the BIO-TEMA project, co-financed by the Fondazione Cassa di Risparmio di Lucca and started exactly two years earlier, ended with interesting results. The project saw the participation of LUCART S.p.A. – a paper company from Lucca – as the supplier of paper sludge, and NUOVA PASQUINI E BINI, which printed the compostable pots containing up to 30% by weight of sludge, the composition of which was developed by the group of Prof. Maurizia Seggiani of the Department of Civil and Industrial Engineering (DICI) of the University of Pisa.
The project set out to create new thermoplastic biocomposites based on biopolymers such as poly lactic acid (PLA) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHB-HV) and cellulosic waste from the paper industry, such as ‘paper sludge’ from chemical-physical purification resulting from the recycling of waste paper.
These sludges, classifiable as non-hazardous waste, have the potential to be successfully used, instead of traditional inorganic fillers (CaCO3), in the production of thermoplastic bio-composites due to their peculiar chemical composition and fibrous morphology. The valorisation of these sludges would lead paper mills to increase the production of recycled paper by closing the production cycle with less environmental impact.
After drying and pulverisation, the sludge supplied by LUCART SPA was used up to 30% by weight in PLA- and PHB-HV-based composites. No problems were encountered in the extrusion phase on a semi-industrial scale, and tensile and impact tests show a mechanical performance adequate for the end use.
On the basis of the results obtained, the two composites with the highest sludge content and good processability were selected, which were produced in granule form by extrusion and used in the subsequent industrial moulding phase conducted at NUOVA PASQUINI E BINI S.p.A. in Altopascio, partner in the project.
In particular, ‘ARA’ model pots with a diameter of 18 cm were produced which are used for floriculture. The moulding did not present any problems. The pots were flexible and passed the crash test conducted on site.
The conclusive tests, concerning the disintegration test in compost according to ISO16929:2013, conducted on portions of moulded pots produced using the PLA-based and PHB-HV-based 30% paper sludge composites, showed that the PLA-based composites passed the test in contrast to the PHB-HV-based composites, due to a lower biodegradation rate leading to a longer time than the 3 months foreseen by the European standard for the disintegration test. Therefore, PLA-based pots turn out to be compostable according to the European standard (EN 13432), and PHB-HV-based pots also turn out to be biodegradable in soil so that they can also be buried together with the plant.
Finally, in order to validate the materials – with a view to a possible application for the production of cultivation pots – phytotoxicity tests were also conducted on the sludge and biocomposites produced with a higher sludge content. This test, based on the germination index (GI) of seeds of Lepidium sativum L., showed that the sludge itself and the composites produced are not potentially phytotoxic; indeed, with 100% eluates of the sludge as is, germination indices well above those found with deionised water and even radicalisation phenomena were detected. This is probably linked to the presence of macro- and micro-nutrients useful to plants such as Calcium, Iron, Potassium, Copper, Zinc, etc..
The application context explored is, therefore, of great interest for the business strategy of the companies involved as they operate in the paper sector (LUCART S.p.A.) and in the moulding of pots (NUOVA PASQUINI & BINI S.p.A.) for nursery gardening. The use of sludge as a filler for thermoplastics can, of course, also be extended to non-compostable plastics, such as PE or PP, which are widely used in the production of pots for nurseries and floriculture to replace traditional inorganic fillers such as calcium carbonate.
The interesting results obtained with the composites developed up to 30% by weight of paper mill sludge in terms of processability with PLA and PHB-HV-based compostable matrices, mouldability (verified at NUOVA PASQUINI & BINI SpA), mechanical properties (tensile strength and impact resistance) and the absence of phytotoxicity, were the subject of a scientific paper published in an international journal (open access), of great popularity in the field of plastic materials, shared with the other two project partners (LUCART S. p.A. and NUOVA PASQUINI & BINI S.p.A.) and with the Fondazione Cassa di Risparmio di Lucca, mentioned as the Project’s financer:
Gigante V., Cinelli P., Sandroni M., D’Ambrosio R., Lazzeri A., Seggiani M. (2021) “On the Use of Paper Sludge as Filler in Biocomposites for Injection Moulding” Materials 14(10), 2688. doi:10.3390/ma14102688