Publicação
New paper functionalization strategies by superficial photopolymerization
| Resumo: | Paper is one of the oldest commodities used by mankind, having helped record its history throughout the ages. However, to talk about paper today, is to talk about something that goes beyond the simple matrix of cellulose fibers used as a support for printing and writing. Due to its biodegradability, recyclability, renewable character, and properties in general, paper is currently exploited in a wide range of applications, such as sensors or diagnostic papers. Yet, one of its most important applications is as a packaging material. To do this, papers are usually coated with a polymer in order to improve their water and air barrier properties. Most coating formulations are still based on polymers obtained from non-renewable sources, such as poly(ethylene-vinyl alcohol) (PEVOH) and polyvinylidene chloride (PVDC). In addition, these formulations rely on the use of volatile organic compounds (VOCs) as organic solvents (e.g. chloroform). With advances made in biomass refining, new biologically sourced and biodegradable polymers, such as poly(lactic acid) (PLA) and poly(hydroxyalkanoates) (PHAs), have been used to replace traditional polymers. However, despite their "greener" characteristics, even these polymers rely on application techniques that require the use of VOCs as solvents. An expedient way to functionalize paper, and of easy industrialization, is the application of photopolymerizable coatings. This type of coatings can be formulated without the use of traditional organic solvents, and the curing process is initiated by the incidence of light (usually UV), which can occur in a few seconds. Many of the monomers and other components used in the formulation of this type of coatings can come from renewable sources, also helping to reduce the current dependence on non-renewable sources. Therefore, the goal of this PhD was the functionalization of paper through the application of photopolymerizable coatings that would give this substrate new functionalities such as hydrophobicity and cholesteric properties. In this context, this work focused on the development of solvent-free formulations, giving priority to the use of renewable raw materials. The study started with the development of a solvent-free photopolymerizable coating based on a copolymer of two acrylic monomers, namely 2-ethylhexyl acrylate and isobornyl methacrylate in a molar ratio of 0.64/0.36, in order to obtain a paper with hydrophobic properties. Two formulations consisting of 50 and 60 wt% copolymer, a mixture of the monomers (in the same molar proportion as the copolymer), and the photoinitiator (PI) darocur 1173 were studied. The application of these formulations resulted in a significant increase in the hydrophobicity of the paper (water contact angle values greater than 120°, and a decrease in water adsorption with Cobb values of 11 g/m2), while maintaining (if not improving) the other properties of the paper, namely the mechanical and air barrier properties. In the same vein, a second solvent-free formulation was developed with the aim of also improving the hydrophobicity of the paper. The formulation was based on tung oil (a highly unsaturated vegetable oil) and Darocur 1173 (PI). The coated papers had their hydrophobicity significantly improved, evidenced by an increase in the water contact angle values from about 71 ° (uncoated paper) to 127 ° and a significant decrease in water absorption, as determined by the Cobb test, from 108 to 17 g/m2 after a curing time of only 15 s. Moreover, with this short curing time, the paper's optical properties (namely whiteness, gloss and opacity) were maintained, and its mechanical properties (namely tensile and burst strength) improved. The last formulation developed is part of a preliminary study, in which the cholesteric properties of aqueous hydroxypropylcellulose (HPC) mixtures were combined with a photopolymerizable system consisting of 2-hydroxyethyl methacrylate (HEMA, monomer) and benzophenone (PI). The aim of these formulations was to develop paper-based moisture sensors capable of changing their color when exposed to atmospheric moisture. The concentration of HPC (65, 68, and 68 wt%) and the HEMA:water ratio (1:2, 1.4:1, 1:1, 1:1.4, 1:2), were adjusted to produce cholesteric papers capable of exhibiting homogeneous color and appropriate moisture response. Preliminary test of exposure of said papers to atmospheres of high relative humidity (95 %) revealed that the color change (ΔE) increased with exposure time, being the color change clearly perceptible (ΔE between 13 and 16). However, further studies are needed in order to better adjust the moisture response of the developed sensors. In summary, the work developed throughout this thesis highlights the possibility of using conventional solvent-free photopolymerizable coatings to manufacture paper-based products with new functionalities. Not only can the formulations developed be easily applied to paper, but the possibility of using renewable materials and short irradiation times allows paper functionalization in an efficient, scalable and environmentally friendly way. This is undoubtedly a promising strategy for developing new paper products with innovative properties. |
|---|---|
| Autores principais: | Silva, Fábio Martins |
| Assunto: | Photopolymerization Coatings Cellulose Paper Packaging Sustainability |
| Ano: | 2023 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | Paper is one of the oldest commodities used by mankind, having helped record its history throughout the ages. However, to talk about paper today, is to talk about something that goes beyond the simple matrix of cellulose fibers used as a support for printing and writing. Due to its biodegradability, recyclability, renewable character, and properties in general, paper is currently exploited in a wide range of applications, such as sensors or diagnostic papers. Yet, one of its most important applications is as a packaging material. To do this, papers are usually coated with a polymer in order to improve their water and air barrier properties. Most coating formulations are still based on polymers obtained from non-renewable sources, such as poly(ethylene-vinyl alcohol) (PEVOH) and polyvinylidene chloride (PVDC). In addition, these formulations rely on the use of volatile organic compounds (VOCs) as organic solvents (e.g. chloroform). With advances made in biomass refining, new biologically sourced and biodegradable polymers, such as poly(lactic acid) (PLA) and poly(hydroxyalkanoates) (PHAs), have been used to replace traditional polymers. However, despite their "greener" characteristics, even these polymers rely on application techniques that require the use of VOCs as solvents. An expedient way to functionalize paper, and of easy industrialization, is the application of photopolymerizable coatings. This type of coatings can be formulated without the use of traditional organic solvents, and the curing process is initiated by the incidence of light (usually UV), which can occur in a few seconds. Many of the monomers and other components used in the formulation of this type of coatings can come from renewable sources, also helping to reduce the current dependence on non-renewable sources. Therefore, the goal of this PhD was the functionalization of paper through the application of photopolymerizable coatings that would give this substrate new functionalities such as hydrophobicity and cholesteric properties. In this context, this work focused on the development of solvent-free formulations, giving priority to the use of renewable raw materials. The study started with the development of a solvent-free photopolymerizable coating based on a copolymer of two acrylic monomers, namely 2-ethylhexyl acrylate and isobornyl methacrylate in a molar ratio of 0.64/0.36, in order to obtain a paper with hydrophobic properties. Two formulations consisting of 50 and 60 wt% copolymer, a mixture of the monomers (in the same molar proportion as the copolymer), and the photoinitiator (PI) darocur 1173 were studied. The application of these formulations resulted in a significant increase in the hydrophobicity of the paper (water contact angle values greater than 120°, and a decrease in water adsorption with Cobb values of 11 g/m2), while maintaining (if not improving) the other properties of the paper, namely the mechanical and air barrier properties. In the same vein, a second solvent-free formulation was developed with the aim of also improving the hydrophobicity of the paper. The formulation was based on tung oil (a highly unsaturated vegetable oil) and Darocur 1173 (PI). The coated papers had their hydrophobicity significantly improved, evidenced by an increase in the water contact angle values from about 71 ° (uncoated paper) to 127 ° and a significant decrease in water absorption, as determined by the Cobb test, from 108 to 17 g/m2 after a curing time of only 15 s. Moreover, with this short curing time, the paper's optical properties (namely whiteness, gloss and opacity) were maintained, and its mechanical properties (namely tensile and burst strength) improved. The last formulation developed is part of a preliminary study, in which the cholesteric properties of aqueous hydroxypropylcellulose (HPC) mixtures were combined with a photopolymerizable system consisting of 2-hydroxyethyl methacrylate (HEMA, monomer) and benzophenone (PI). The aim of these formulations was to develop paper-based moisture sensors capable of changing their color when exposed to atmospheric moisture. The concentration of HPC (65, 68, and 68 wt%) and the HEMA:water ratio (1:2, 1.4:1, 1:1, 1:1.4, 1:2), were adjusted to produce cholesteric papers capable of exhibiting homogeneous color and appropriate moisture response. Preliminary test of exposure of said papers to atmospheres of high relative humidity (95 %) revealed that the color change (ΔE) increased with exposure time, being the color change clearly perceptible (ΔE between 13 and 16). However, further studies are needed in order to better adjust the moisture response of the developed sensors. In summary, the work developed throughout this thesis highlights the possibility of using conventional solvent-free photopolymerizable coatings to manufacture paper-based products with new functionalities. Not only can the formulations developed be easily applied to paper, but the possibility of using renewable materials and short irradiation times allows paper functionalization in an efficient, scalable and environmentally friendly way. This is undoubtedly a promising strategy for developing new paper products with innovative properties. |
|---|
Atividades financiadas
Não foram encontrados projetos financiados.