Abstract

Abstract

In recent years exponential increase in the use of adhesives in industrial processes is observed. Nowadays these materials are used in applications as diverse as aerospace industry, automotive industry, railway industry or even civil construction. In the same way, the use of composite materials has grown enormously, especially in the aerospace industry, thanks to the benefits that this type of materials are able to provide, even as reinforcement.

Current bus structures present serious problems of fatigue due to their rigidity, resulting in unexpected failures in certain nodes where stresses are concentrated. This work is part of a project that it is trying to provide more elasticity to the structure through the use of a new CFRP node joined by adhesives to the bus structure using polyurethane.

The complex design of the node has caused numerous manufacturing problems. PLA node was manufactured using 3D printing for being used as a core. PLA node was covered layer by layer with CFRP by hand lay-up. In order to know the behavior of the whole set (CFRP node, adhesive and steel beams), four prototypes were manufactured and tested. Four point flexural test was carried out on the prototypes to validate the assembly. Results show the suitability and capacity of this new node concept to be used in bus structures.

In recent years exponential increase in the use of adhesives in industrial processes is observed. Nowadays these materials are used in applications as diverse as aerospace industry, automotive industry, railway industry or even civil construction. In the same way, the use of composite materials has grown enormously, especially in the aerospace industry, thanks to the benefits that this type of materials are able to provide, even as reinforcement.

Current bus structures present serious problems of fatigue due to their rigidity, resulting in unexpected failures in certain nodes where stresses are concentrated. This work is part of a project that it is trying to provide more elasticity to the structure through the use of a new CFRP node joined by adhesives to the bus structure using polyurethane.

The complex design of the node has caused numerous manufacturing problems. PLA node was manufactured using 3D printing for being used as a core. PLA node was covered layer by layer with CFRP by hand lay-up. In order to know the behavior of the whole set (CFRP node, adhesive and steel beams), four prototypes were manufactured and tested. Four point flexural test was carried out on the prototypes to validate the assembly. Results show the suitability and capacity of this new node concept to be used in bus structures.

Abstract

During the last years, composites based on renewable sources gained significant interest due to a globally increased awareness on sustainability. In order to address these challenges and to achieve ambitious sustainability targets, such as the reduction of greenhouse gas emissions, Covestro recently introduced composites from a new aliphatic and bio-based polyurethane, which bears a bio-content of ca. 70%. A combination of such bio-based polyurethanes with bio-based reinforcing fibers can lead for the first time to a composite with a bio-content of appr. 90%. Due to the aliphatic nature of the bio-based isocyanates, the resulting composites are characterized by an inherent UV- and weathering resistance, which makes them primarily suitable for outdoor applications and allows to omit additional protective coatings steps. A corresponding matrix material for pultruded composites, which is based on conventional raw materials, was launched under the brand name Desmocomp®.     

Abstract

Thermosets comprise a family of chemically cross-linked networks formed by irreversible chemical reactions, resulting in polymers with outstanding properties such as superior mechanical properties, high thermal stability and chemical resistance. However, their high stability precludes reprocessing or recycling, thus making it difficult to move towards a circular economy and sustainability. During the last years, research has focused on dynamic chemistry, in order to introduce reversible bonds along the polymer chain and synthesize reprocessable and/or recyclable thermosets. In this context, the Diels-Alder reaction is of special interest, as it can give thermoreversible reactions with a relatively low coupling and high decoupling temperature. Within this work, a trifunctional polyol containing the furan-maleimide Diels-Alder adduct has been developed to facilitate the recycling of cross-linked polyurethanes. The maleimide-furan adduct forms covalent bonds at low temperatures, but when heated these bonds break down, splitting the polymer chain into smaller chains and softening the polymer, allowing it to be reprocessed. Then, when the temperature drops, the bonds between the maleimide and the furan are reformed and the polymer regains its mechanical properties. Thereby, a thermoset polyurethane was synthesized reacting the triol containing Diels-Alder adduct with a polymeric isocyanate. The reprocessability and/or recyclability of the synthesized polyurethane was then evaluated by breaking it into small pieces and reprocessing them by pressing at high temperature, in order to obtain new sheets and evaluate their mechanical properties, being similar to the original ones.

Abstract

Abstract

The development of sustainable composites has become in a major strategy for different sectors, such as the offshore renewable energy industry.

Thermoset polyurethanes (PUR) offer some advantages for their use in structural composite parts, like their good thermal properties, adhesion with different types of fibers, ultra-fast curing, low viscosity and corrosion resistance, highlighting their resistance to fatigue and consequent durability. However, PUR have some environmental drawbacks, such as their petrochemical origin and low recyclability.

Consequently, biobased PUR (BIO-PUR) formulated based on polyols derived from vegetable oils have aroused keen interest. Moreover, it is possible to incorporate recycled monomers in their formulation, which are obtained from highly degraded plastics collected from the sea.

In addition, it is necessary to consider the PUR end of life to improve the composite sustainability. An interesting solution is the incorporation of dynamic bonds into the PUR network, with reversible capacity such as Diels-Alder, to improve the polymer recyclability.

Therefore, this work has focused on the development of a new formulation of BIO-PUR with the required mechanical properties for structural applications in the marine environment. In addition, the integration of recycled monomers and DA bonds have been explored to improve the circularity of the developed resin. To this end, aspects ranging from analysis and synthesis to the characterization of the resins have been covered.

Abstract

The present work is part of the characterization of glass fiber composites elaborated with a novel vinylester-urethane resin, with addition of poly for use in reinforcing materials for concrete, as a passive reinforcement or as a reinforcement for structures in use, as these resins have a higher Resistance to chemical agents, basics and vapors along with a lower exotherm facilitating the manufacture of thick laminates.Within Mode II fracture mechanics, until this 2014 there was no standard that would collect a procedure to quantify GIIC. Davies through the European Structural Integrity Society (ESIS) issued a mode II test protocol in 1992 known as ENF (End Notch Flexure) [1]ASTM D7905-14 encompasses a fairly complex procedure in which the basis for the characterization of shear fracture toughness in mode II using the final notch flexure (ENF) test is laid.This paper aims to verify the main differences between this classical procedure and the method of this standard to verify their similarities.For this purpose, a mechanical pre-characterization of the reinforced resin is carried out with high-grade fabric (780 g/cm2) with glass fiber E as well as a thinner carbon fiber composite. This characterization is performed by ENF bending tests, and the procedure of the new ASTM D-7905 standard.   [1] ASTM D5528-01, “Standard Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites”, American Society for Testing and Materials, 2001.

Abstract

The idea of ​​recycling waste materials from such different sectors as textile or  automotive has been popular for decades, but today's recycling methods often produce poor quality products that are difficult to reuse. In the specific case of thermoset composites the problem is even greater, since once the resin is cured its dissolution is not possible and therefore the recovery of the original fiber and resin becomes practically unfeasible. This work presents recyclable thermoset composites made with fabrics obtained from waste textiles and epoxy or polyurethane resins, whose crosslinking is based on reversible bonds, which confers them the ability to be dissolved in a specific agent, so that both the fiber and the resin can be recovered for subsequent reuse. Taking into account the particularities of the starting raw materials, the manufacturing parameters of the composites and the resin dissolution conditions have been studied and optimized. The work is part of the European project Trash-2-Cash, which proposes a new model in which waste from paper and textiles are recycled chemically,in order to obtain fabrics with the same quality as the initial ones, to manufacture innovative products such as recyclable thermoset composites that can be industrially produced and recycled at the end of life.