RESUMO

In this work, blends based on poly (lactic acid) (PLA)/acrylonitrile-butadiene-styrene (ABS) compatibilized with maleic anhydride-grafted (SEBS-g-MA) were prepared in a co-rotational twin-screw extruder by varying the concentrations of the compatibilizing agent. The influence of the compatibilizing agent on the morphology, mechanical, thermal, thermomechanical, and rheological properties of the prepared materials was analyzed. The effect of annealing on the properties of the blends was also investigated using injection-molded samples. The X-ray diffraction (XRD) results proved that the increments in crystallinity were an effect of annealing in the PLA/ABS/SEBS-g-MA blends, resonating at higher heat deflection temperatures (HDTs). The impact strength of the PLA/ABS blends compatibilized with 10 wt% SEBS-g-MA was significantly increased when compared to the PLA/ABS blends. However, the hardness and elastic modulus of the blends decreased when compared to neat PLA. The refined morphology shown in the scanning electron microscopy (SEM) analyses corroborated the improved impact strength promoted by SEBS-g-MA. The torque rheometer degradation study also supported the increased compatibility between SEBS-g-MA, PLA, and ABS. The TGA results show that the PLA/ABS and PLA/ABS/SEBS-g-MA blends are more thermally stable than the neat PLA polymer at higher temperatures. The results showed that the ideal composition is the heat-treated PLA/ABS/SEBS-g-MA (60/30/10 wt%), given the high impact strength and HDT results. The results of this work in terms of mechanical improvement with the use of compatibilizers and annealing suggest that the PLA/ABS/SEBS-g-MA system can be used in the production of 3D-printing filaments.

RESUMO

The poultry industry, highly prevalent worldwide, generates approximately 7.7 × 106 metric tons of chicken feathers (CFs), which become a major environmental challenge due to their disposal when considered waste or due to their energy transformation consumption when considered by-products. CFs are mainly composed of keratin (approximately 90%), which is one of the most important biopolymers whose inherent characteristics make CFs suitable as biopolymer fibers (BPFs). This paper first assesses the morphological and chemical characteristics of these BPFs, through scanning electron microscopy and energy dispersive X-ray spectroscopy, and then evaluates the waste valorization of these BPFs as a sustainable alternative for fiber-reinforcement of earthen mixes intended for earthen construction, such as adobe masonry, rammed earth, and earthen plasters. In particular, four earthen mixes with increasing doses of BPFs (i.e., 0%, 0.25%, 0.5%, and 1% of BPFs by weight of soil) were developed to evaluate the impact of BPF-reinforcement on the capillary, mechanical, impact, and abrasion performance of these earthen mixes. The addition of BPFs did not significantly affect the mechanical performance of earthen mixes, and their incorporation had a statistically significant positive effect on the impact performance and abrasion resistance of earthen mixes as the BPF dose increased. On the other hand, the addition of BPFs increased the capillary water absorption rate, possibly due to a detected increment in porosity, which might reduce the durability of water-exposed BPF-reinforced earthen mixes, but a statistically significant increment only occurred when the highest BPF dose was used (1%).

RESUMO

ABSTRACT Objective The aim of the present study was to evaluate the mechanical and thermal characteristics of two denture base acrylic resins containing silver nanoparticles (AgNPs). Material and Methods Two different acrylic denture base resins (heat-polymerized and microwave polymerized) containing 0.3, 0.8 and 1.6 wt% AgNPs were evaluated for flexural strength, elastic modulus and impact strength. The glass transition temperature (Tg) and relative heat capacity (Cp) of the samples were determined from the Differential Scanning Calorimetry (DSC) results. For statistical analysis, two-way ANOVA and Tukey-HSD tests were performed. Results Addition of 0.8% and 1.6% AgNPs in microwave-polymerized resin significantly decreased the transverse strength and elastic modulus. In terms of impact strength, the addition of AgNPs has no effect on both resin groups. Glass transition temperature (Tg) was decreased with the addition of AgNPs for both denture base resins. Conclusions The incorporation of AgNPs, generally used for antimicrobial efficiency, affected the transverse strength of the denture base acrylic resins depending on the concentration of nanoparticles. Tg was decreased with the addition of AgNPs for both denture base resins.

Assuntos

RESUMO

This study evaluated the impact strength of a denture base resin (Lucitone 550-L) and four reline resins (Tokuyama Rebase II-T; Ufi Gel Hard-U; New Truliner-NT, and Kooliner-K), both intact and in a reline combination (L/L, L/T, L/U, L/NT, and L/K). For each group (n = 20), half of the specimens were thermocycled before testing. Charpy tests were performed, and the impact strengths were calculated. Data were analyzed by two-way analyses of variance and Tukey's test (p = 0.05). For the intact groups, mean impact strength values for L (1.65 and 1.50) were significantly higher than those of the reline resins (0.38-1.17). For the relined groups, the highest mean impact strength values were produced by L/T (5.76 and 5.12), L/NT (6.20 and 6.03), and L/K (5.60 and 5.31) and the lowest by L/U (0.76 and 0.78). There were no significant differences between L and L/L. Thermocycling reduced the impact strength of T (from 0.73 to 0.38) and L/L (from 1.82 to 1.56).

RESUMO

Water may influence the mechanical properties of the acrylic resins. Thus, the effect of water storage on the impact strength (IS) of one denture base (Lucitone 550 - L) and four reline resins (Tokuyama Rebase II - T; UfiGel Hard - U; Kooliner - K; New Truliner - NT) was evaluated. Bars of L were made (60 x 6 x 2 mm) and relined (2 mm) with T, U, K, NT and L. Intact specimens of each material (60 x 6 x 4 mm) were also fabricated for comparative purposes. Specimens were submitted to Charpy impact tests without water storage (control) and after immersion in water for 7, 90 and 180 days. Data (kJ/m²) analyzed by two-way ANOVA and Tukey's test (p=0.05) revealed that after 90 days, U exhibited an increase in the IS (0.93) compared to 7 days (0.58). K (1.48) and L/K (7.21) exhibited a decrease at the 7-day period (1.01 and 3.23, respectively). NT (0.60) showed an increase in the IS after 180 days (1.52), whereas L/NT (7.70) showed a decrease (3.17). Water immersion improved the IS of U and NT, and decreased the IS of K, L/K, and L/NT. Water may affect differently the IS of acrylic resins and, consequently, the resistance to fracture of relined denture bases.

A água pode influenciar as propriedades mecânicas das resinas acrílicas. Assim, o efeito do armazenamento em água na resistência ao impacto (RI) de uma resina para base de prótese (Lucitone 550-L) e quatro materiais reembasadores (Tokuyama Rebase II-T; UfiGel Hard-U; Kooliner-K; New Truliner-NT) foi avaliado. Barras da resina L foram confeccionadas (60 x 6 x 2 mm) e reembasadas (2 mm) com T, U, K, NT e L. Amostras não reembasadas de cada material também foram confeccionadas (60 x 6 x 4 mm) para fins comparativos. As amostras foram submetidas aos testes de impacto tipo Charpy sem armazenamento (controle) e após imersão em água por 7, 90 e 180 dias. Os resultados (kJ/m²) analisados por meio de ANOVA dois fatores e teste de Tukey (p=0,05) revelaram que, após 90 dias, U exibiu aumento na RI (0,93) comparado com 7 dias (0,58). K (1,48) e L/K (7,21) exibiram diminuição no período de 7 dias (1,01 e 3,23, respectivamente). NT (0,60) apresentou aumento na RI após 180 dias (1,52), enquanto L/NT (7,70) apresentou redução (3,17). A imersão em água melhorou a RI de U e NT e diminuiu a RI de K, L/K, e L/NT. A água pode afetar de maneira diversa a RI das resinas acrílicas e, consequentemente, a resistência à fratura das bases de próteses reembasadas.

Assuntos

RESUMO

The addition of different polymers, such as polytetrafluorethylene (PTFE), to denture base resins could be an option to modify acrylic resin mechanical properties. This study evaluated the surface hardness, impact and flexural strength, flexural modulus and peak load of 2 acrylic resins, one subjected to a long and another subjected to a short polymerization cycle, which were prepared with or without the addition of 2 percent PTFE. Four groups were formed according to the polymerization cycle and addition or not of PTFE. Forty specimens were prepared for each test (10 per group) with the following dimensions: hardness (30 mm diameter x 5 mm thick), impact strength (50 x 6 x 4 mm) and flexural strength (64 x 10 x 3.3 mm) test. The results of the flexural strength test allowed calculating flexural modulus and peak of load values. All tests were performed in accordance with the ISO 1567:1999 standard. Data were analyzed statistically by ANOVA and Tukey's test with the level of significance set at 5 percent. No statistically significant differences (p>0.05) were found for surface hardness. Flexural strength, impact strength and peak load were significantly higher (p<0.05) for resins without added PTFE. The flexural modulus of the acrylic resin with incorporated 2 percent PTFE polymerized by long cycle was significantly higher (p<0.05) than that of the other resins. Within the limits of this study, it may be concluded that the addition of PTFE did not improve the mechanical properties of the evaluated acrylic resins.

A adição de diferentes polímeros como o politetrafluoretileno (PTFE) às resinas para base de próteses removíveis pode ser uma opção para modificar as propriedades mecânicas das resinas acrílicas. Este estudo avaliou a dureza de superfície, a resistência ao impacto e à flexão, o módulo flexural e a carga de ruptura de duas resinas acrílicas, uma submetida ao ciclo longo e a outra ao ciclo curto de polimerização, as quais foram preparadas com ou sem a adição de PTFE a 2 por cento. Quatro grupos foram formados de acordo com os ciclos de polimerização e a adição ou não de PTFE. Quarenta espécimes foram preparados para cada teste (10 espécimes por grupo) com as seguintes dimensões: dureza de superfície (30 mm diametro x 5 mm espessura), resistência ao impacto (50 x 6 x 4 mm), resistência à flexão (64 x 10 x 3,3 mm). O módulo flexural e a carga de ruptura foram calculados a partir dos valores obtidos no teste de resistência à flexão. Todos os testes foram realizados em conformidade com a Norma ISO 1567:1999. Os dados foram submetidos à análise de variância e teste de Tukey com nível de significância de 5 por cento. Não foram encontradas diferenças estatisticamente significantes (p>0,05) para dureza de superfície. Os valores de resistência à flexão, resistência ao impacto e carga de ruptura foram maiores para as resinas sem a adição de PTFE (p<0,05). O valor do módulo flexural da resina acrílica com adição de PTFE a 2 por cento, polimerizada por ciclo longo, foi maior do que as outras resinas (p<0,05). Dentro das limitações deste estudo, pode-se concluir que a adição de politetrafluoretileno não melhorou as propriedades mecânicas das resinas acrílicas avaliadas.

Assuntos

RESUMO

OBJECTIVES: This study evaluated the impact and flexural strength and analyzed the fracture behavior of acrylic resins. METHODS: Eighteen rectangular specimens were fabricated of Lucitone 550, QC 20 (both unreinforced acrylic resins), Impact 1500 (extra strength impact), Impact 2000 (high impact) according to the manufacturers' instructions. The impact strength was evaluated in notched specimens (50x6x4mm) and flexural strength in unotched (64x10x3.3mm), using three-point bending test, as well as, stress at yield, Young modulus and displacement at yield. Fragments from mechanical tests were observed by SEM. Data from impact strength, stress at yield and displacement at yield were analyzed by 1-way ANOVA and Tukey test (alpha=0.05). Young modulus values were analyzed by One-way ANOVA and Dunnett T3 multiple comparisons test (alpha=0.05). RESULTS: Mean values of impact strength and stress at yield values were higher (P<.005) for Impact 2000 while Young modulus was higher (P<.05) for Lucitone 550; Impact 1500 and Impact 2000 showed significant values (P<.05) in the displacement at yield. Impact fractures of the all acrylic resins were brittle. Bending fractures of Lucitone 550 and Impact 2000 were brittle, QC 20 fractures were ductile and Impact 1500 showed brittle (75%) and ductile (25%) fractures. CONCLUSION: Within the limitations of this study, the Impact 2000 showed improved mechanical properties with high capacity of stress absorption and energy dissipation before the fracture.