of the Maritime University of Szczecin
Akademii Morskiej w Szczecinie
2015, 44 (116), 14–18
ISSN 1733-8670 (Printed) Received: 31.08.2015
ISSN 2392-0378 (Online) Accepted: 06.11.2015
DOI: 10.17402/050 Published: 07.12.2015
Technology of single polymer polyester composites
and proposals for their recycling
Maciej Gucma
1, Katarzyna Bryll
1, Katarzyna Gawdzińska
1, Wojciech Przetakiewicz
1Elżbieta Piesowicz
21
Maritime University of Szczecin
1–2 Wały Chrobrego St., 70-500 Szczecin, Poland
e-mail: {m.gucma; k.bryll, k.gawdzinska, w.przetakiewicz}@am.szczecin.pl
2
West Pomeranian University of Technology, Faculty of Mechanical Engineering and Mechatronics 19 Piastów Ave., 70-313 Szczecin, Poland, e-mail: elzbieta.piesowicz@zut.edu.pl
corresponding author
Key words: manufacturing, single polymer, composite, materials, recycling, sea transport Abstract
A single polymer composite comprises a composite built out of fibres and a matrix, both made of the same or a very similar polymer material, where the components may differ with: molecular mass, density or branching degree. Such thermoplastic composites provide the beneficial mechanical characteristics required for reinforced materials, and their great advantage is the ease of full material recycling after the end of use. The aim of the presented work is to provide a description of the manufacturing technology, with a definition of the possibility for the waste of single polymer polyester composites to undergo a full material recycling process, oriented towards use in shipbuilding. A proposed idea for recycling is in the preparatory stage and its assumptions and the process followed will be the subject of a patent application. This work forms part of the studies realized in the scope of the REP-SAIL Project under the ERA-NET Transport III Initiative Future Travelling, carried out at the Maritime University of Szczecin, and the prepared doctoral thesis entitled “Manufacturing, shaping of operational properties and recycling of single polymer composite materials”.
Introduction
The concept of a composite material is used in many branches of technology. Still, there is no universal definition which takes in all composite materials. One of the most frequently cited defini-tions is the four-element definition formulated in 1967 by L.J. Broutman and R.H. Krock, according to which:
a composite is a material made artificially; a composite must be composed of at least two
materials (Figure 1) with different chemical or physical properties, and with a distinct border between the components (the reinforcement and the matrix phase);
the components characterize a composite with their volume fractions;
a composite has characteristic properties, which are not present in its separate components
(Chand, Kreuzberg & Himichsen, 1994; La-croix, Werwer & Schulte, 1997; LaLa-croix, Lu & Schulte, 1999).
Figure 1. Structure of a composite material
At this point, it is necessary to understand that regardless of which definition is used to describe these materials, the matrix and the reinforcement phases are always present. These phases have certain functions to fulfil and they complement
Matrix
each other. The reinforcing phase is usually a much more rigid material, of better mechanical properties than the matrix, and it improves the operational properties of a composite (Pornnimit & Ehrenstein, 1991; Kmetty, Bárány & Karger-Kocsis, 2010; Gao et al., 2012; Fakirov, 2013; Karger-Kocsis & Bárány, 2014). The matrix is a component which is continuous, it surrounds other phases and usually gives shape to the product. Because the reinforcing phase is usually not continuous, the matrix phase also allows carrying loads between components. The properties of a composite are dependent on many factors, such as: the properties of the compo-nent phases, their relative amount and geometry, which is: size of particles, the shape and orientation and arrangement of the reinforcing phase in the matrix, as well as the strength of the interphase boundaries. Different classifications of composite materials are presented in the relevant literature (Gao et al., 2012). These are usually divided ac-cording to the matrix material or the reinforcing
phase. According to the matrix criterion, these materials are divided into polymer, metal or ce-ramic matrix composites. Only the polymer com-posites are the subject of the presented work, be-cause these materials are presently the largest production group. The matrix is usually formed out of thermohardening resins – phenol resins or mela-mine resins, chemically hardened resins, such as polyester or epoxide resins and out of thermoplastic materials, among others – polyethylene, polyamide and polyesters. The reinforcing phase can be formed out of materials such as polyurethane foams, polyester, glass or natural fibres, such as cellulose, flax or sunn hemp. The connection of these elements allows unique properties to be obtained, which are useful in many branches of industry – mostly for the polyester-glass compos-ites, manufactured using lamination technology. In shipbuilding, these composites are used for hulls, superstructures and fuel tanks (Capiati & Porter, 1975; Matabola et al., 2009; Karger-Kocsis &
Fakirov, 2012). These materials are also used in boatbuilding and machine industry. In Poland, they are used to produce yachts and floating equipment, rotors of wind power plants (Figure 2), containers and pipes, moulding compounds, tubs, waterslides for swimming pools, infrastructure elements, etc.
The total value of the worldwide polymer com-posite market is estimated to be 60 milliard dollars and it is growing year on year, therefore a method of management of after-use and after-manufactur-ing waste needs to be proposed. Statistical data reveals that in Poland, at the beginning of XXI century, the amount of waste originating from manufacturing exceeded 2000 t/year, while the after-use waste was around 20,000 t/year. Nowa-days, each new material accepted for mass produc-tion must be subjected to material recycling or at least energy-from-waste. This is why it is so impor-tant to define the recycling possibilities of poly-mers, particularly polymer composites, because according to the 2008/98/WE directive, it is a necessary and essential process (Pornnimit & Ehrenstein, 1991; Lacroix, Lu & Schulte, 1999; Dorigato & Pegoretti, 2012; Gao et al., 2012; Karger-Kocsis & Bárány, 2014). The recycling term means any recovery process, in which waste materials are reprocessed into products, materials or substances used either for the original purpose or for other purposes. It comprises the reprocessing of organic material, but it does not include the recov-ery of energy and reprocessing into materials which can be used as fuels or for excavation filling. The problem of the management of rubber or polyester-glass laminates waste, for example, is not yet solved (Capiati & Porter, 1975; Karger-Kocsis & Bárány, 2014). This problem is increasing due to the gradual decommissioning of floating units constructed of laminates. One solution to this problem is the application of material recycling, consisting in the breaking up of waste and its application as fibres or filling for new products. However, this type of recycling does not solve the problem, as a new product is manufactured, which frequently has mechanical properties worse than the initial composite and will also need to be managed later. Another solution, in the case of laminates, is energy-from-waste, in which a composite is burned, but this type of reclamation is also not free from faults, as waste still remains as the reinforcing phase, such as glass fibres, is not destroyed. This all means that a search for new materials or matrix-fibre set-ups, aimed at replacing these traditional composites is required (Lacroix, Werwer & Schulte, 1997; Matabola et al., 2009).
An interesting innovation regarding the facilita-tion of recycling, both in material and energy terms, is a proposal to use reinforcement in the form of thermoplastic fibres made out of the same material as the matrix, which results in obtaining a single polymer composite. In recent years, single polymer composites are increasingly frequently becoming the subject of scientific studies. In literature, studies into this type of material are usually described using the examples of polyethylene or polypropyl-ene single polymer composites. However, the idea of single polymer composites is also starting to be implemented for other polymer materials, such as PMMA or polyesters. One of the polyester materi-als is the subject of the presented study. The aim of the work was to describe manufacturing technology with a determination of the possibilities for process-ing waste of sprocess-ingle polymer polyester composites, fully subjected to material recycling, made for use in shipbuilding.
Study material and technology of single polymer polyester composites
The concept of a single polymer composite comprises a composite of fibres and a matrix, made out of the same or a very similar polymer material, where the components may differ with: a molecular mass, density or branching degree. Such thermo-plastic composites provide a solution to the re-quirement for reinforced materials with beneficial mechanical properties, for which full material recycling can easily be carried out after end of use.
In the scope of the presented work, the materials presented in Table 1 were manufactured. They are a combination of two types of matrices: polyester waste matrix, obtained from a PET-G recyclate and pure PET-G foil bought to build a model composite and compare its morphology and properties with the recyclate composite.
Table 1. Study material – single polymer polyester compo-sites
No. Matrix Reinforcement
1 Polyester (PET G)
long ordered polyester fibres in the fabric form
2 Polyester (PET G)
long ordered polyester fibres in the yarn form
3 Polyester (PET G)
long disordered polyester fibres in the loose form
4 Polyester recyclates (PET G)
long disordered polyester fibres in the fabric form
5 Polyester recyclates (PET G)
long ordered polyester fibres in the yarn form
6 Polyester recyclates (PET G)
long disordered polyester fibres in the loose form
For all the materials mentioned above, polyester reinforcement was applied. As a reinforcing phase, continuous fibres in the form of ordered yarn and fabric were used, as well as in unordered form. The reinforcement was applied. All six material types will also be subjected to recycling to determine and compare their properties and evaluate the possibili-ties of recycling single polymer polyester materials. The results of these studies will be presented in successive future publications by the authors.
The materials were manufactured using a film-stacking technology on a prepared and modified laboratory test stand, located in the Faculty of Mechanical Engineering and Mechatronics at the West Pomeranian University of Technology. The scope of manufacturing of the composites included the following stages of the manufacturing process: preparation of the reinforcement and matrix phases,
drying, press moulding (in two stages – softening and integration), cooling, removing a product from the mould and finishing processing (Figure 3).
Figure 4. Examples of the macrostructures of manufac-tured single polymer material. Parameters of the process: temperature: 235C, saturation pressure: 2.5 MPa for 60 s, drying: 24 h in temperature of 60C. Cooling: glycol-water solution. Pressed without additional plates, only on a frame with separators out of kapton
Figure 3. Stages of manufacturing of single polymer composite material on a modified laboratory test stand
The parameters of the process were selected ex-perimentally, for example using analysis of defects arising during the manufacturing process. Examples of the macrostructures of the manufactured material are shown in Figure 4. Various shapes of rein-forcement and sample types are visible.
In the images in Figure 4, obtained using a scanning electron microscope (SEM), correct connection of the matrix and the reinforcement is visible (Figure 5), which is proof of a well con-ducted manufacturing process.
Conclusions
The current level of advancement of work on single polymer polyester composites is a basis for the recycling concept presented in Figure 6. This concept is in a preparatory phase and its assump-tions and rules for the process will be the subject of a patent application. Proposals for the recycling of single polymer composites will also include analy-sis of the influence of the reinforcing phase on the matrix of the manufactured composites and the strength, impact and structural tests. They will be a basis for the application of modern single poly-mer materials in the shipbuilding industry, e.g. for building hulls of boats, along with proposals for their recycling.
Acknowledgments
This article presents the results of the REP-SAIL Project under the ERA-NET Transport Initiative Future Travelling Call co-financed by Polish Na-tional Center for Research and Development.
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