Propriedades adesivas de polímeros biodegradáveis derivados do glicerol com adição de nanowhiskers de celulose

• Ano de defesa: 2017
• Autor(a) principal: Figueiredo, Lucas Ricardo Fernandes
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Brasil; UFRN; PROGRAMA DE PÓS-GRADUAÇÃO EM CIÊNCIA E ENGENHARIA DE MATERIAIS
• Palavras-chave em Português: Compósitos; Nanowhiskers de celulose; Adesivos biodegradáveis; Degradação; CNPQ::ENGENHARIAS::ENGENHARIA DE MATERIAIS E METALURGICA
• Link de acesso: https://repositorio.ufrn.br/jspui/handle/123456789/25053

“Green adhesives” are of great scientific and technological interest as an alternative to conventional commercial products, which often release toxic substances and take long time to degrade. However, the poor mechanical properties and fast degradation of some biodegradable polymers limit their use in most practical applications. In the present work, novel biodegradable composites were prepared using biodegradable polymers and cellulose nanowhiskers (CNW) for their use as wood adhesives. The goal of the investigation was to study the effect of the addition of CNW on the mechanical properties and degradation of the polymers. The biodegradable polymers synthesized by polycondensation based on glycerol and acids were poly(glycerol adipate) - PGA, poly(glycerol maleate) - PGM, poly(glycerol citrate) - PGC, poly(glycerol phthalate) - PGPh, poly(glycerol succinate) - PGSu and poly(glycerol sebacate) - PGS. In addition, the copolymers synthesized were poly(glycerol succinate-co-maleate) - PGMSu, poly(glycerol succinate-co-adipate) – PGASu and poly(glycerol adipate-co-maleate) – PGMA. Cellulose nanowhiskers (CNW) were added to the polymers as an approach for improving the mechanical properties and controlling the degradation rate. Composites were produced with the addition of 0, 5, 10 and 20 wt.% of CNW. The neat polymers and composites were analyzed by Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). Adhesively bonded joints were produced in test specimens of slash pine (Pinus elliottii) and angelim (Vatairea heteroptera Ducke) and subjected to accelerated aging and tested under shear by tensile loading. Bonded joints produced with polyvinyl acetate - PVAc and cyanoacrylate based adhesives were also tested under the same conditions for comparison purposes. Thermal analyses indicated that most of the biodegradable glycerol-based polymers tested are stable up to about 260°C and the addition of CNW increased the thermal stability (Tonset) of some polymers by 26°C up to 48°C, while others were not affected. Analyses of the fracture surfaces after the shear tests by Scanning Electron Microscopy (SEM) suggest less ductile fracture with the incorporation of CNW to the adhesive. The shear strengths of the green adhesives developed from glycerol with 10 and 20 wt.% CNW were greater than that of the commercial PVAc based adhesive. The best results of shear strengths were obtained for PGASu 20 wt.% CNW (2.57 ± 0.36 MPa) and PGM 20 wt.% CNW (2.33± 0.43 MPa), while the shear strength for polyvinyl acetate - PVAc was 1.58 ± 0.18 MPa. Aging improved the shear strength of some adhesives. The best result was obtained for PGMA 20 wt.% CNW, which reached (3.89 ± 0.74 MPa) after 250h of aging, thus greater than the shear strength of cyanoacrylate (3.12 ± 0.53 MPa). Ultimately, the results presented in this work suggest that the addition of cellulose nanowhiskers (CNW) is a viable approach to tailor mechanical properties and degradation of biodegradable polymers.