ABSTRACT
Ethylene-vinyl acetate copolymer (EVA) with 19% of vinyl acetate and its derivatives modified by hydrolysis of 50 and 100% of the initial vinyl acetate groups were used to produce blends with thermoplastic starch (TPS) plasticized with 30 wt% glycerol. The blends were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, water absorption, stress-strain mechanical tests, dynamic mechanical analysis and thermogravimetric analysis. In contrast to the blends with unmodified EVA, those made with hydrolyzed EVA were compatible, as demonstrated by the brittle fracture surface analysis and the results of thermal and mechanical tests. The mechanical characteristics and water absorption of the TPS were improved even with a small addition (2.5 wt%) of hydrolyzed EVA. The glass transition temperature rose with the degree of hydrolysis of EVA by 40 and 50°, for the EVA with 50 and 100% hydrolysis, respectively. The addition of hydrolyzed EVA proved to be an interesting approach to improving TPS properties, even when very small quantities were used, such as 2.5 wt%.
ABSTRACT
Self-organized block copolymer structures derived from dewetting of thin films are becoming important in nanotechnology because of the various spontaneous and regular sub-micrometric surface patterns that may be obtained. Here, we report on the self-organization of a poly(styrene)-b-poly(ethene-co-butene-1)-b-poly(styrene) triblock copolymer during drying of its solution over a mica substrate. Regular submicrometric arrangements with long-range order were formed at critical polymer concentrations, consisting of parallel ribbons and hexagonal arrays of dots (droplets). This variety of highly ordered structures is explained by the interplay between forming mechanisms, mainly due to "fingering instabilities" at the three-phase line of the copolymer solution during drying. The thickness of the structures was "quantized" due to the microphase separation of the block copolymer. The formation of hexagonal patterns may be attributed to Marangoni instability at the liquid film surface prior to dewetting.
ABSTRACT
Identificar a ocorrencia de sintomas osteomusculares em professores do ensino fundamental. Metodo: foi utilizado um questionario com um inventario sobre dados gerais e ocupacionais e o questionario nordico. Para a analise estatistica foram comparados os sujeitos com e sem sintomas nos ultimos 12 meses, independente da regiao e considerando as mais afetadas. Foi realizada analise de regressao logistica univariada e multivariada com um nivel de significancia de 5 por cento. Para a analise multivariada, foi utilizado o criterio Stepwise. As variaveis foram analisadas pelo teste de associacao Qui-Quadrados ou teste de Fisher. Resultados: a idade media dos participantes foi de 40 anos, 99,4 por cento eram mulheres, sendo que, 90,4 apresentaram sintomas osteomusculares. As areas mais atingidas foram: lombar, toracica, cervical, ombros, punhos e maos. A presenca de dor associou-se significativamente com a ausencia de filhos (p=0,03) e com o tempo de atuacao profissional menor ou igual a 15 anos (p=0,03). Na analise multivariada, a presenca de dor na regiao cervical (OR=6,2, IC a 95 por cento=1,4 - 26,7), nos ombros (OR=2,8, IC a 95 por cento=1,1 - 7,2), na regiao toracica (OR=2,5, IC a 95 por cento= 1,1 - 5,5) e punhos e maos(OR=2,0 IC a 95 por cento=1,0 - 3,9) apresentou associacao significativa para a idade menor que 30 anos, sujeitos entre 30 e 39 anos, ausencia de filhos e nao ter uma uniao estavel, respectivamente. Conclusao: os professores apresentaram elevada ocorrencia de sintomas osteomusculares e confirmam a necessidade de novos estudos