3,488 research outputs found
In vitro assessment of the enzymatic degradation of several starch based biomaterials
The susceptibility of starch-based biomaterials to enzymatic degradation by amylolytic enzymes (glucoamylase
and α-amylase) was investigated by means of incubating the materials with a buffer solution, containing
enzymes at different concentrations and combinations, at 37 °C for 6 weeks. Two polymeric blends of corn
starch with poly(ethylene-vinyl alcohol) copolymer and poly(Є-caprolactone), designated by SEVA-C and
SPCL, respectively, were studied. The material degradation was characterized by gravimetry measurements,
tensile mechanical testing, scanning electron microscopy (SEM), and Fourrier transform infrared-attenuated
total reflectance (FTIR-ATR). The degradation liquors were analyzed for determination of reducing sugars,
as a result of enzyme activity, and high performance anion exchange chromatography with pulsed
amperometric detection (HPAEC-PAD) was used to identify the degradation products. All of the analysis
performed showed that starch polymeric blends are susceptible to enzymatic degradation, as detected by
increased weight loss and reducing sugars in solution. α-Amylase caused significant changes on the overall
mechanical properties of the materials, with a decrease of about 65% and 58% being observed in the moduli
for SEVA-C and SPCL, respectively, when compared with the control (samples incubated in buffer only).
SEM analysis detected the presence of fractures and pores at the material’s surface as a result of starch
degradation by amylolytic enzymes. FTIR spectra confirmed a decrease on the band corresponding to
glycosidic linkage (-C-O-C-) of starch after incubation of the materials with α-amylase. In contrast, the
incubation of the polymers in buffer only, did not cause significant changes on the material’s properties and
morphology. Comparing the two materials, SEVA-C exhibited a higher degradability, which is related to
the physicochemical structure of the materials and also to the fact that the starch concentration is higher in
SEVA-C. The identification of the degradation products by HPAEC-PAD revealed that glucose was the
major product of the enzymatic degradation of starch-based polymers. α-Amylase, as expected, is the key
enzyme involved in the starch degradation, contributing to major changes on the physicochemical properties
of the materials. Nevertheless, it was also found that starch-based polymers can also be degraded by other
amylolytic enzymes but in a smaller extent.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BPD/5744/2001 - Programa Operacional "Ciência, Tecnologia, Inovação (POCTI ) - União Europeia. Fundo Europeu de Desenvolvimento Regional (FEDER)
NUMERICAL STUDY OF HEAT TRANSFER IN EXTENDED SURFACESWITH MUTUAL RADIATION BETWEEN PARALLEL FINS
The present work shows the influence of the mutual heat transfer on the effectiveness of finned surfaces. Numerical simulations are carried out through a sequence of linear problems, possessing an equivalent minimum principle, that has as its limit the solution of the original problem. The original nonlinear problem is regarded as the limit (which always exists) of a sequence of linear problems like the classical conduction-convection ones. In this work the nonlinear conduction-radiation heat transfer process is considered and simulated by means of a finite difference linear scheme. Such a limit is reached in an easy way by means of standard procedures, allowing the employment of more realistic hypotheses, like some nonlinear boundary conditions, since the mathematical complexities are not a constraint for simulating the elliptic partial differential equation. This work accounts for the the steady state heat transfer process in rigid fins which experiences convective and radiative heat exchange. Some typical results are shown in order to illustrate the methodology. Results have shown both the relevance of the radiation and the importance of the thermal interaction between the fins, so that there is an effective and realistic thermal mapping. Neglecting the thermal interaction can lead to errors of up to 20 percent
Stochastic theory of non-equilibrium wetting
We study a Langevin equation describing non-equilibrium depinning and wetting
transitions. Attention is focused on short-ranged attractive
substrate-interface potentials. We confirm the existence of first order
depinning transitions, in the temperature-chemical potential diagram, and a
tricritical point beyond which the transition becomes a non-equilibrium
complete wetting transition. The coexistence of pinned and depinned interfaces
occurs over a finite area, in line with other non-equilibrium systems that
exhibit first order transitions. In addition, we find two types of phase
coexistence, one of which is characterized by spatio-temporal intermittency
(STI). A finite size analysis of the depinning time is used to characterize the
different coexisting regimes. Finally, a stationary distribution of
characteristic triangles or facets was shown to be responsible for the
structure of the STI phase.Comment: To appear in Europhys. Lett. // 3 figure
Gestão de políticas públicas: análise do plano nacional de promoção das cadeias de produtos da sociobiodiversidade.
Esta pesquisa objetiva analisar a elaboração do Plano Nacional de Promoção das Cadeias de Produtos da Sociobiodiversidade - PNPSB a partir da metodologia proposta por Dagnino (2013). Com levantamento de documentos, foi possível analisar o PNPSB com a metodologia proposta nas etapas de elaboração, implantação e avaliação do Plano
Adaptabilidade e estabilidade de cultivares de milho no Meio-Norte do brasileiro: safra 2004/2005.
Characterisation and application of glycanases secreted by aspergillus terreus CCMI 498 and trichoderma viride CCMI 84 for enzymatic deinking of mixed office wastepaper
Two enzymatic extracts obtained from xylan-grown Aspergillus terreus CCMI 498 and cellulose-grown Trichoderma
viride CCMI 84 were characterised for different glycanase activities. Both strains produce extracellular endoxylanase
and endoglucanase enzymes. The enzymes optimal activity was found in the temperature range of 45-60 ºC.
Endoglucanase systems show identical activity profiles towards temperature, regardless of the strain and inducing
substrate. Conversely, the endoxylanases produced by both strains showed maximal activity at different pH values
(from 4.5 to 5.5), being the more acidic xylanase produced by T. viride grown on cellulose. The endoglucanase activities
have an optimum pH at 4.5-5.0. The endoxylanase and endoglucanase activities exhibited high stability at 50 ºC and
pH 5.0. Mannanase, β-xylosidase, and amylase activities were also found, being the first two activities only present for
T. viride extract. These two enzymatic extracts were used for mixed office wastepaper (MOW) deinking. When the
enzymatic extract from T. viride was used, a further increase of 24% in ink removal was obtained by comparison with
the control. Both enzymes contributed to the improvement of the paper strength properties and the obtained results
clearly indicate that the effective use of enzymes for deinking can also contribute to the pulp and paper properties
improvement.PRAXIS/BIO/1133/95.
BIC/3087/96, BD/3253/96
Estabilidade produtiva de cultivares de milho nos cerrados do Meio-Norte Brasileiro: periodo 2002 a 2004.
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