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The objective of the PAPYRUS project is to study and reuse paper mill fibre byproducts in composite and plastics processing applications. The project is co-financed by AGRICE, the scientific interest group of the French Environment and Energy Management Agency, ADEME, and led by the Pole Européen de Plasturgie (PEP). Partners in the project are Papeteries Emin-Ledier, the National Institute for Agricultural Research (INRA) in Reims and the compounder, AD Majoris.
(Published on January-February 2009 – JEC Magazine #46)
CHARLYSE POUTEAU, PROJECT MANAGER, PÔLE EUROPÉEN DE PLASTURGIE
The goal of the PAPYRUS project is to study the reuse of paper fibre by-products in plastics processing applications. These end-of-life fibres that cannot be recycled are introduced as reinforcement in a thermoplastic matrix by means of compounding. The introduction of these fibres constitutes an important step on the path to replacing materials derived from fossil resources, while offering additional properties. The fibres separated in this way are quite long but they are associated with thermoplastic compounds with the potential to act as "coupling agents" between fibres and matrix. What is more, paper mill fibres offer a stable supply of stocks in terms of both quality and quantity, to suit the demands of plastics processors (high tonnage, less dependent on the fluctuating and seasonal markets in agricultural fibres, offering the possibility of just-in-time processing with no need to store fibres). The potential applications of these new composites involve many sectors (automotive, furnishings, leisure, etc.). The ultimate objective of this project is to provide costcompetitive materials with valuable properties (environmental, mechanical, lighter than other composites, etc.).
The progress of the project and its sticking points
The sticking points encountered in the incorporation of these paper fibres are identical to those encountered for natural fibres: water absorption, sensitivity to temperature, and fibre-matrix interface. These sticking points may be alleviated/limited by means of appropriate processing technologies, the introduction of specific additives and a correctly chosen application. Nonetheless, the use of these fibres requires specific preparation, since they are in clod-like form upon leaving the paper manufacturing process. These fibre agglomerates therefore need to be broken down, dried and ground. PEP has developed a specific procedure for doing just this (Fig. 1).
After preparation, the fibres are incorporated in a thermoplastic matrix by twin-screw compounding, then the compounds are injected. The material characteristics are then analysed in order to evaluate the impact of the nature and quality of the fibres, the type of matrix (two matrices of different polarities have been tested), the formulation (introduction of coupling agents, fibre ratio) and the mixing process (dispersion of fibrous agglomerates, distribution of fibres in the matrix), (Fig. 2).
Some significant results ...
The average length of the fibres obtained following processing has been evaluated at 750 microns (by reflection microscopy, Olympus DP software).
Impact of the addition of coupling agent
A composite (PP) reinforced with 30% by weight of paper fibre will see its tensile modulus increase by 12% and its tensile strength increase by 26% following the 4% addition of a maleic anhydride-based coupling agent. The unnotched impact properties also increase significantly as opposed to notched impact, in line with the tests carried out on other fibres.
Impact of the type of matrix
The tensile moduli of materials that are reinforced with 30% by weight of these paper fibres are increased respectively by a factor of 1.5 and 2.5 for PP and PCL matrices compared to a virgin matrix.
Influence of mixing and dispersion
The materials were mixed several times in the compounder to observe changes in the mechanical properties and how the fibre was dispersed. As early as the second mixing step, a maximum tensile modulus of 3,000 MPa and a tensile strength of 43 MPa are obtained, so demonstrating optimised dispersion (Fig. 3).
Comparison with other fibres
In order to be able to rank this fibrous resource against those that are generally available on the market, we compared it with flax and wood fibres.
Composites reinforced with 30% by weight of paper fibres offer equivalent mechanical properties to those of composites reinforced with wood but inferior still to those reinforced with flax fibres (1,000 MPa lower tensile modulus and 10 MPa lower tensile strength), (Fig. 4).
Influence of the fibre moisture content
Fibre conditioning tests under controlled humidity conditions followed by their incorporation in a PP matrix showed an impact on the properties of the composite.
It has been observed that the conditioning of fibres in 85% relative humidity (9.5% moisture content) or by a spray humidification method (100% moisture content) demonstrates Young's modulus variations of 100 MPa between the two formulations. What is more, drying of the pellets prior to injection also demonstrates a modulus increase in the order of 200 MPa.
Conclusion and outlook
The properties of the composites studied in the framework of the PAPYRUS project are encouraging.
Initial results demonstrate improved mechanical properties entirely on a par with those of wood fibre composites, although still inferior to flax fibre composites.
These fibres also present an economic advantage since what is involved here is the re-use of by-products that are as yet underexploited. There still remains a great deal of work to be done in order to process these fibres on an industrial scale. It would be great to get a specialist in the domain onboard ... so watch this space!!