Materials Today Communications
A versatile route to the synthesis of pressure-sensitive adhesives and polyHIPE-like microparticles: an experimental study on glycerol valorization
Graphical Abstract
Introduction
Several raw materials from renewable sources are being used as monomers intended to produce new polymeric materials. The main advantages of these promising renewable monomers are associated with high availability, low cost and high potential for modifying its structure through chemical functionalization. Such substances may be of interest in the industry as they generally exhibit: i) reactive functional groups (carbonyl, hydroxyl) required for functionalization and polycondensation, and ii) conjugated double bonds and unsaturation which allow structural modifications that are fundamental for the synthesis via polyaddition reactions in efficient polymerization processes, such as suspension, emulsion and miniemulsion. These characteristics allow its use in the formulation of different materials of high industrial interest, as for instance, paints, adhesives, resins, thermoplastics, thermosets, among others [[1], [2], [3], [4]].
In Brazil, high amounts of glycerol are being produced due to the great expansion of the biodiesel industry. A significant market growth has been observed since 2008, when biodiesel became mandatory in the energy matrix at a percentage of 2 wt% of the total composition of diesel oil. As a Brazilian government initiative, the amount of biodiesel has been increased over the years, reaching a fraction of 10 wt% in relation to diesel in March 2018. However, the addition of biodiesel causes an increase in the amount of glycerol obtained as a side product of the glyceride transesterification in the biodiesel process. Considering that the industrial market is at the limit of absorption of this by-product as a result of the gradual increase in the glycerol availability, the searches for processes in order to convert glycerol into valuable products is of fundamental importance to overcome this technological issue [5,6].
Pressure sensitive adhesives (PSA) are materials that adhere to different surface types at room temperature without the use of high-pressure surface contact that can be applied on the adhesive film to allow the joining of materials. Thus, PSA are generally solid, soft and viscoelastic materials which after short contact times adhere to surfaces by means of Van der Waals forces [7]. Moreover, the adhesiveness to various surfaces is a property called tack and is determined by the material ability to quickly wet the contact surface, whose adhesive nature is highly dependent on both glass transition temperature (Tg) and molar mass distribution (MMD) of the polymeric adhesive, and these two fundamental properties can be tailored in order to modulate the adhesion ability to adhere to a variety of substrates [8]. These materials find their main applications in the production of adhesive tapes and labels, Post-It notes, temporary surface protection in the automotive industry, packaging labels and tapes for the consumables industry, double sided tapes for the microelectronic component industry, among others [9].
Considering PSA by using monomers from renewable sources, the use of acrylic and epoxy substances and materials stand out. Biobased monomers can be obtained by structural modification of natural materials such as cellulose, glucose [10], resins, vegetable oils and their constituents (triglycerides and fatty acids), terpenes, among others [1,11,12]. Thus, biobased acrylic PSA can be obtained similarly to acrylic PSA, which use an acrylic monomer that normally originates polymer of low Tg in combination with monomer able to form homopolymers with high Tg values (e.g. styrene, methyl methacrylate, vinyl pivalate, among others) [7], making these biobased materials, with unique, improved or competitive properties, compared to adhesives from petrochemical sources [8,13].
Polymeric materials exhibiting a polyHIPE structure consisting of highly porous structures are normally synthesized through emulsion templating obtained with high internal phase emulsion process. It is generally agreed that a polyHIPE is a porous emulsion templated polymer synthesized within HIPE (N. B. a high viscous emulsion system, with a droplet phase normally occupying more than 74 wt% of the total dispersion system, whose internal morphology may be converted into open or closed cells) [14,15]. These classes of highly porous polymers are characterized by the presence of rigid structures containing cavities interconnected by pores. Several polyHIPE can be synthesized by choosing appropriately the component and process operating conditions, which lead to formation of very attractive materials for numerous technological applications, as for instance, heterogeneous catalysts, absorption, adsorption, thermal insulators, template of carbon materials, catalysts supports, among others [[16], [17], [18], [19]].
In the present work, glycerol (Gly) is functionalized, via acid catalysis, with acrylic acid (AA), to obtain a macromonomer n-acylglycerol (n-ACC). The macromonomer was used in suspension copolymerization reactions with styrene (Sty). The reactions were carried out with different compositions of monomers to produce materials with distinct characteristics such as microparticles with polyHIPE-like porous structure and copolymer resins with properties similar to pressure sensitive adhesives (PSA). To the best of our knowledge, the present work illustrates for the first time the production of copolymers based on styrene and glycerol-based macromonomer exhibiting polyHIPE-like porous structure or PSA features depending on the suspension process operating conditions. These materials were characterized by NMR (1H and 13C), FT-IR, SEM, DSC, DTG, gravimetric analysis, mechanical test and tack of pressure-sensitive adhesives by rolling ball.
Section snippets
Experimental Section
Styrene/n-acylglycerol (n-ACC) copolymers were synthesized through suspension polymerization in accordance with the main steps depicted in Fig. 1, as follows: i) n-ACC macromonomer formation through glycerol esterification with acrylic acid catalyzed by methane sulfonic acid, and ii) suspension copolymerizations of n-acylglycerol and styrene carried out with different n-ACC mass fractions to form microparticles with polyHIPE-like porous structure and polymer resins with pressure sensitive
FTIR Analysis
The macromonomer n-ACG is formed by reactions occurring between different esters (monoacylglycerol, diacylglycerol and triacylglycerol) formed during the process that was characterized by FTIR (Fig. 2). The infrared analysis allows us to infer that the macromonomer is formed via polycondensation reactions. Such inference is possible due to the large reduction in band intensity attributed to the stretching of the hydroxyl groups (region between 3600-2700 cm-1), as well as due to the displacement
Conclusions
The current paper focused on the valorization of glycerol with emphasis on the synthesis and characterization of a macromonomer n-acylglycerol (n-ACG), which is derived from glycerol by esterification reactions with acrylic acid. Polymerization reactions were performed to incorporate and add value to materials derived from renewable sources such as n-ACG (versatile glycerol-based monomer, presenting double-bonds functionality to undergo free-radical polymerizations). To this end, styrene/n-ACG
Author Statement
And all authors certify that they have participated sufficiently in the work to take public responsibility for the content, including participation in the concept, design, analysis, writing, or revision of the manuscript.
Furthermore, each author certifies that this material or similar material has not been and will not be submitted to or published in any other publication before its appearance in the Polymer.
Author Contributions
All authors have contributed to the writing of the manuscript and they all have given approval to the final version of the manuscript.
There are no conflicts to declare.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors thank Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) – Finance code 001, Fundação de Apoio à Pesquisa do Distrito Federal (FAPDF) and Embrapa Agroenergy for the mechanical tests.
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2022, Ceramics InternationalCitation Excerpt :Their adhesive properties can be further optimized by employing acrylic monomers with a hydroxyl group and carboxylic acid, which engage in crosslinking of acrylic copolymers. Although acrylate-based PSAs have been widely used for manufacturing of automotive components to electronics [6,7], the low thermal conductivity limits their application as thermal interface materials. In order to surmount this hurdle, considerable efforts have been made to increase the thermal conductivity of polymer composites by incorporating thermally conductive ceramics such as aluminum oxide [8], aluminum nitride [9], and boron nitride [10–12] into the polymer matrix.
Characterization of expanded polystyrene waste as binder and coating material
2022, Case Studies in Construction MaterialsCitation Excerpt :Experimental tests with adhesive films of different thicknesses show that the distance of the rolling ball is inversely proportional to the thickness of the adhesive film. These results show that the stickiness obtained in the evaluated wastes are significantly lower than that obtained with styrene / n-ACG copolymers synthesized with 20% by weight of n-ACG, in which rolling ball distances of 44 mm were obtained [38]. Or else, obtained with hydrogenated dicyclopentadiene hydrocarbon resin grafted with propylene in which rolling ball distances less than 20 cm have been reported [36,37].
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Current address: Universidade Federal do Oeste da Bahia, Centro das Ciências Exatas e das Tecnologias, Campus Reitor Edgard Santos, CEP: 47810-059, Barreiras, BA, Brazil