Composites based on a thermoset phenolic matrix and jute fibers were prepared and characterized. The fibers were alternatively treated with ionized air or aqueous alkaline solution (mercerization) with the aim of introducing changes in the morphology, dispersive component of surface free energy, γS D (estimated by Inverse Gas Chromatography, IGC) and the acid/base character of their surfaces, shown by their ANs/DNs ratio (estimated by IGC), and their degree of crystallinity. The final objective was to investigate the influence of these modifications on the adhesion at the jute fiber/phenolic matrix interface in the composites. The untreated jute fiber showed 50% crystallinity, γS D=18 mJ m- 2 and ANs/DNs= 0.9 (amphoteric surface), tensile strength = 460 MPa and maximum elongation = 0.7%, while the respective composite had an impact strength of 72.6 J m- 1. The treatments positively modified the fibers and the adhesion at the interface was better in the composites reinforced with treated fibers than with untreated fibers. The best set of results was exhibited by the fiber treated with 10% NaOH [46% crystallinity, γS D = 26 J m- 2 (phenolic matrix γS D = 32 J m- 2), ANs/DNs = 1.8 (surface predominantly acidic, similar to phenolic matrix, ANs/DNs = 1.4), tensile strength approximately 900 MPa, maximum elongation = 2%, impact strength of respective composite approximately 95 J m- 1)]. The fibers treated for 5 h with ionized air exhibited favorable properties [(45% crystallinity, γS D = 27 J m- 2, ANs/DNs = 2.1 (acidic surface)] for further use as reinforcement of a phenolic matrix, but their partial degradation during the treatment decreased their tensile properties (395 MPa and 0.5% for tensile strength and maximum elongation, respectively) and their action as reinforcement (impact strength of the respective composite approximately 73 J m- 1).

Neste trabalho, foram utilizadas fibras de curauá como reforço de matriz termoplástica de biopolietileno de alta densidade. O polietileno foi obtido por polimerização de eteno, gerado do etanol de cana de açúcar. Este polímero é também chamado de biopolietileno (BPEAD), por ser preparado a partir de material oriundo de fonte natural. Desta forma, pretendeu-se contribuir para desenvolver materiais que, dentre outras propriedades, causem menor emissão de CO2 para a atmosfera na sua produção, utilização e substituição, comparativamente a outros materiais. Adicionalmente, polibutadieno líquido hidroxilado (PBHL) foi acrescentado à formulação do compósito, visando a um aumento na resistência à propagação da trinca durante impacto. Os compósitos e as fibras foram caracterizados por várias técnicas, tais como microscopia eletrônica de varredura (MEV), Calorimetria Exploratória Diferencial (DSC), Termogravimetria (TG), além da caracterização dos compósitos quanto à Análise Térmica Dinâmico-Mecânica (DMTA), propriedades mecânicas (impacto e flexão) e absorção de água. A presença das fibras de curauá diminuiu algumas propriedades do BPEAD, como resistência ao impacto. A análise de DMTA mostrou que as fibras geram material mais rígido. Pode-se considerar que a introdução de PBHL na formulação do material foi eficiente, levando a uma resistência ao impacto do compósito BPEAD/PBHL/Fibra maior do que a do compósito BPEAD/Fibra.

In this work, curaua fibers were used in the reinforcement of a high-density (HDPE) thermoplastic matrix. The polyethylene used was obtained by polymerization of ethene produced from sugarcane ethanol. This polymer, also called high-density biopolyethylene (HDBPE), was prepared from a natural source material. The aim was to contribute to developing materials which could lead to smaller release of CO2 into the atmosphere in comparison to other materials. Additionally, liquid hydroxylatedpolybutadiene (LHPB) was added to the composite formulation, aiming at improving resistance to crack spreading during impact. The fibers and their composites were characterized by several techniques, such as scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermal gravimetry (TG). The composites were also characterized by dynamic mechanical thermal analysis (DMTA), mechanical properties (flexural and impact strength), and water absorption. The presence of curaua fibers reduced some of the properties of HDBPE, such as flexural and impact strength. DMTA indicated a more rigid material with the fibers incorporated. The addition of LHPB to the formulation was efficient, leading to greater impact strength for the HDBPE/LHPB/Fiber composite, as compared to the HDBPE/Fiber composite.