Análise dinâmico-mecânica: aplicações em filmes comestíveis

Mendieta-Taboada, Oscar; Carvalho, Rosemary Aparecida de; Sobral, Paulo José do Amaral

doi:10.1590/s0100-40422008000200035

Cited by 7 publications

(3 citation statements)

References 89 publications

(153 reference statements)

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“…Finally, the endothermic event present in the DSC curves of the hydrogels between −50 and 0°C can be identified as changes in the structure of the material, that is, movements of groups or parts of lateral groups of the polymer chain 64 . Conversely, the event observed near a temperature of 150°C may be related to the onset of degradation of hydrogel components, which, according to the TGA results, begins at approximately 120°C.…”

Section: Resultsmentioning

confidence: 99%

Synthesis and characterization of hydrogels from alginate and ora‐pro‐nóbis (Pereskia aculeata Miller) mucilage

de Morais,

Ferreira,

de Oliveira Meira

et al. 2023

J of Applied Polymer Sci

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This study aimed to synthesize and characterize hydrogels prepared with alginate (ALG) and ora‐pro‐nobis mucilage (MOPN) by ionic gelation. The hydrogels were produced from solutions containing 0.5, 0.75, 1.0, and 1.25% (w/v) sodium alginate, 0.25, 0.5, 0.75, 1.0 and 1.25% (w/v) MOPN and 1.5 and 3.0% (w/v) CaCl2. The hydrogels were characterized in terms of mechanical strength, degree of swelling, morphology, chemical groups by Fourier transform infrared spectroscopy (FTIR) and x‐ray diffraction (XRD); and their thermal properties were assessed by differential scanning calorimetry (DSC) and thermogravimetric and differential thermal analysis (TG/DTA). The results indicated that MOPN acted with ALG in chain crosslinking, confirming its ability to interact with other polymers to form gels. The control hydrogel, composed of only ALG (1.5%), showed a more crosslinked and less amorphous structure with greater thermal resistance, while the hydrogel composed of ALG (1.25%) and MOPN (0.25%) showed a more amorphous, porous structure with lumps. However, these treatments were statistically equal in terms of mechanical strength and degree of swelling, indicating that ALG and MOPN hydrogels are an economically viable alternative to ALG‐only hydrogels, where 0.25% (w/v) of the ALG can be replaced by MOPN without significant changes in its mechanical and swelling properties.

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Section: Resultsmentioning

confidence: 99%

Synthesis and characterization of hydrogels from alginate and ora‐pro‐nóbis (Pereskia aculeata Miller) mucilage

de Morais,

Ferreira,

de Oliveira Meira

et al. 2023

J of Applied Polymer Sci

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show abstract

“…Assim materiais mais rígidos irão apresentar valores de tanδ menores e, do mesmo modo, materiais mais flexíveis irão apresentar valores de tanδ maiores [20] . A Figura 4, apresenta o comportamento da tangente de perda para os compósitos que apresentaram melhores resultados de E' e E".…”

Section: Análise Térmico Dinâmico-mecânica (Dmta)unclassified

Propriedades térmicas e mecânicas dos compósitos de Polipropileno pós-consumo reforçados com fibras de celulose

et al. 2017

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ResumoForam investigadas as propriedades térmicas e mecânicas de compósitos de polipropileno reciclado e virgem, reforçados com até 40% em peso de fibras de celulose (FC), bem como a morfologia da matriz polimérica. Para a obtenção dos dados, foram utilizadas as técnicas de Análise Témica Dinâmico-Mecânica (DMTA), Calorimetria Exploratória Diferencial (DSC) e Microscopia Eletrônica de Varredura (MEV). Os resultados mostraram que os compósitos de polipropileno reciclado,com percentagem de 30% FC e os compósitos de polipropileno virgem, com percentagem de 20% FC, tiveram um aumento significativo nos valores de módulo de armazenamento (E') e grau de cristalinidade (χ c ), indicando com isso uma resistência mecânica mais elevada. Já nas amostras com 40% FC, houve uma diminuição na rigidez do material. Estes resultados foram confirmados por MEV, onde observou-se a aglomeração das fibras de celulose na matriz. Não houve alteração nas temperaturas de transição vítrea (T g ) e fusão cristalina (T m ) dos compósitos produzidos. Palavras-chave: compósitos de polipropileno, fibras de celulose, compósitos pós-consumo. AbstractThe thermal and mechanical properties of composite recycled and virgin of polypropylene were investigated, reinforced with up to 40% by weight of cellulose fibers (FC), as well as the morphology of the polymer matrix. To obtain the data, techniques for Dynamic-Mechanical Thermal Analysis (DMTA) were used, Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM). The results showed that recycled polypropylene composites with a percentage of 30% FC and virgin polypropylene composites with a percentage of 20% FC had a significant increase in storage modulus values (E') and degree of crystallinity (χc), indicating a higher mechanical strength in these composites. Since the samples with 40% FC, there was a decrease in the stiffness of the material. These results were confirmed by the SEM, where noted agglomeration of the cellulose fibers in the matrix. There was no change in the glass transition temperature (Tg) and crystalline melting temperature (Tm) of the produced composite.

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“…A temperatura de transição vítrea é definida como a temperatura na qual o polímero amorfo passa do estado vítreo para o estado líquido "termoplástico" (CALLISTER, 2007). Em temperaturas abaixo da Tg (estado vítreo), o filme se comporta como um vidro frágil, e em temperaturas acima de Tg (estado borrachoso), o filme é mais mole, flexível e possui características plásticas, pois as cadeias poliméricas começam a apresentar movimentos de rotação e de translação (CALLISTER, 2007;TABOADA;. Um material é geralmente mais estável no estado vítreo (abaixo da temperatura de transição vitrea, Tg) do que no estado borrachoso (IWAMOTO et al, 1999).…”

Section: Filmes Biodegradáveisunclassified

Instrumentação para a caracterização dielétrica de filmes biodegradáveis

Cremasco¹

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The dielectric characteristics of a material can be used as a non-destructive technique to evaluate and monitor the quality as well as the understanding of the structure-property of a material, through its dielectric properties as a function of frequency, temperature, chemical composition of the material, among others. In the literature there are few studies and data of dielectric characterization of films based on biopolymers. In this context, the objective of this research was the development and construction of an alternative instrumentation equipment on the market, such as network and impedance analyzers, which could be used for the dielectric characterization of biodegradable films based on gelatin. The method of parallel plates was used to determine the real part of permittivity known as relative permittivity or dielectric constant (ε'). The circuit used for the instrumentation was an astable oscillator operation based on operational amplifier (741) switched by the load of a parallel plate capacitor whose dielectric was a sample of the biodegradable film. From the values of the oscillation frequency and geometry of the capacitor, it was possible to calculate the capacitance of each sample and thus obtaining values of the relative permittivity of the film, using well established basic relationships. Gelatin films were produced by casting technique being used as plasticizer glycerol (G), sorbitol (S) and mixtures thereof, in proportion (G:S) 30:70, 50:50 and 70:30. The films were characterized for moisture and crystallinity. The relative permittivity (ε') of the films, determined at room temperature, was evaluated as a function of frequency (5-50 kHz), storage time, moisture content and type of plasticizer. The designed and constructed instrumentation was able to accurately measure the relative permittivity of the samples, being that this property decreased with increasing frequency for all films. Keeping constant frequency, there was no variation in ε' for the gelatin films, independent of the plasticizer over one month of storage at 24 ± 3 ⁰C. The moisture effect was observed at frequencies lower than 25 kHz, how bigger the moisture content the higher the relative permittivity. The effect of the plasticizer type in relative permittivity of the films were observed at low frequency (5 kHz) and plasticized films with sorbitol have higher ε' values. The plasticized films with higher moisture content exhibit lower crystallinity, hence larger molecular mobility and consequently higher the relative permittivity.

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Análise dinâmico-mecânica: aplicações em filmes comestíveis

Cited by 7 publications

References 89 publications

Synthesis and characterization of hydrogels from alginate and ora‐pro‐nóbis (Pereskia aculeata Miller) mucilage

Synthesis and characterization of hydrogels from alginate and ora‐pro‐nóbis (Pereskia aculeata Miller) mucilage

Propriedades térmicas e mecânicas dos compósitos de Polipropileno pós-consumo reforçados com fibras de celulose

Instrumentação para a caracterização dielétrica de filmes biodegradáveis

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