Study of the properties of an epoxy adhesive with additions of a residue from the biodiesel production process

https://doi.org/10.1016/j.ijadhadh.2020.102701Get rights and content

Abstract

In order to increase fuel supplies and reduce the gaseous emissions responsible for global warming, the production of biofuels has been stimulated. However, Biodiesel production leads to a huge amount of residues. The inappropriate discard of these residues generates an environmental problem. An important co-product of the transesterification process for biodiesel production is glycerol (also known as glycerin), representing 10% of the processed mass. Therefore, there are studies being carried out for the proper destination of glycerol. From these studies, one application of glycerol that deserves special attention is in the production of polymers. In this sense, this work studies the possibility of incorporating crude glycerol in epoxy adhesives, where fractions of 1.0%, 2.5%, 5.0% and 10.0% were added into epoxy. The tests carried out were tensile tests, adhesion tests and dynamic mechanical analysis (DMA), in order to evaluate the mechanical, adhesives and thermal behavior of the epoxy with these additions. In conclusion, small fractions of glycerol, like 1.0%, showed satisfactory results, in general, not decreased in adhesive properties; in opposite it leads to a small improvement with need more studies. With 2.5% and 5.0% of addition, more investigation is advisable. However, it was observed indications of improvement in properties, although less than those obtained with 1.0%. With 10.0% of addition there were sharp deterioration of properties, showing that use with 10.0% is not recommendable.

Introduction

In order to increase fuel supplies and reduce the gaseous emissions responsible for global warming, the production of biofuels has been stimulated. This growth of production also provides more opportunities in rural communities and develops a plan to replace fossil reserves, which are finite [1]. Biofuels can be used directly or through changes in internal combustion engines. Also, they partially or totally replace fossil fuels in other forms of energy generation.

Biodiesel is produced mostly from soybeans in Brazil. However, the sustainability of this production is questionable. The large landowners dominate the production of soy, to the detriment of small producers, concentrating the land [2]. These landowners have been responsible for the increasing deforestation of Brazilian native forests. Still, soybeans are grown with a high pesticide load, which results in contamination of the water [2]. On the other hand, in the quest to make biodiesel production more sustainable, we highlight the demand for the reuse of its waste. As a consequence of the increase in the production of biodiesel, there is a high amount of resulting co-products. Among the residues, we highlight the generation of crude glycerol, and the researches in search of ways to add value to this co-product [3]. The current market for the consumption of glycerol is specific and restricted, so it is essential to intensify the consumption of glycerol to make biodiesel production competitive [4]. Therefore, it is necessary to look for new technological and product routes for glycerol, besides its transformation, since the usual processes of purification are too expensive [5].

The high impurity level of crude glycerol limits its application, mainly in food and pharmaceutical industries, in which the glycerol from biodiesel can't be used for this reason. However, there are a growing number of studies for the application of glycerol as a raw material for polymer blends, mainly as plasticizing agent [4].

Polymers and polymer blends have been increasingly replacing traditional engineering materials such as metals, glass and wood. In addition, glycerol can be polymerized so as to form a thermoset polymer [5]. In this sense, it is justified to investigate possible applications for this by-product of biodiesel production. In the present work, this is done by incorporating the residue, the crude glycerol, into an adhesive based on epoxy resin. Epoxy-based adhesives have been modified to meet market requirements, which seek to improve the properties of the final product. In this way it, as examples, it can be cited some works like FU et al. [6], also MARTINS et al. [7] and MARTINS et al. [8] and many other studies like SOARES et al. [9], BARCIA et al. [10], NGUYEN et al. [11]. In addition, one of the main use is the production of epichlorhydrin, which can be seen in SANTACESARIA et al. [12], KOČÍ1 AND LOUBAL [13] and production of liquid epoxy resin from epichlorohydrin.

The main objective of this work is to study the effects of the addition of biodiesel residue, glycerol in the epoxy resin, verifying the impact on its mechanical, thermomechanical and adhesive properties. For that, a methodology of characterization of these materials was used, with respect to its properties showing promising results with 1.0% of addition.

Section snippets

Epoxy resin based adhesive

The following materials were used, to prepare the specimens to tests:

  • Base: MC 109 of EPOXYFIBER manufacturer;

  • Hardener: FD 131 from EPOXYFIBER manufacturer;

  • Fractions of biodiesel residue (glycerol).

The procedure for the manufacture of the epoxy resin is to mix the base, in this case the diglycidyl ether of bisphenol A (DGEBA), with hardener, the aliphatic amine, mixed ratio of epoxy and hardener 5:1, this fraction recommended by supplier - for the beginning of the polymerization process - for

Tests carried out

For the analysis of the mechanical properties of the epoxy adhesives with and without addition of glycerol, the following tests were performed:

  • Tensile test;

  • DMA (Dynamic-Mechanical Analysis);

  • Adhesion Test (“Lap Shear").

Tensile tests

Results of the tensile tests are presented with the stress versus strain curves in the following Fig. 2, Fig. 3. These were performed at a constant velocity of 2 mm/min in the equipment described above using the 10 kN load cell at room temperature. Samples were analyzed without crude glycerol addition and with: 1.0%, 2.5%, 5.0% and 10.0% of crude glycerol. Adhesive without the addition of the residue from now on will be called pure. Firstly, three epoxy samples with 1.0% glycerol were tested,

Conclusion

Based on the results obtained in the tests performed on the samples with each fraction of glycerol, we can conclude that:

One percent of crude glycerol addition to the epoxy did not decrease the adhesion ability capacity of the adhesive, which is very interesting in the reuse of this residue.

With two and a half and Five percent of crude glycerol addition in the epoxy resin presented increased the stiffness of the adhesive and decreased the ductility, and it can be undesirable when used to

Acknowledgments

The authors wish to thank Professor Silvio de Barros (CEFET-RJ) and the student Brenno Duarte (CEFET-RJ) for their cooperation in the adhesion tests, and to Professors Lavinia Borges and Daniel Castello (COPPE/UFRJ), for the opportunity to use the DMA, also to the employees and students of the Laboratory of Industrial Processes and Nanotechnology (LPIN/UEZO).

References (21)

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