a b s t r a c tIn this work, the affinity of water to cassava thermoplastic starch (TPS) and PBAT blend films with the addition of surfactant Tween 80 was investigated. The TPS and PBAT blend films were produced by extrusion with different starch concentrations added with 2% surfactant Tween 80, without surfactant Tween 80 or with 100% starch films (F100) as controls. The sorption isotherms, water vapor permeability (WVP), solubility coefficients, and diffusion coefficients of the films were evaluated. F100 films demonstrated the highest WVP and solubility coefficient values. Addition of the surfactant increased the diffusion coefficient and WVP. Films with the addition of surfactants had lower structural integrity and mechanical resistance than control films. The results indicated that the surfactant increased the free volume between the starch chains, thus, favoring the diffusion of water vapor. The combined effects of solubility coefficients and diffusion coefficients controlled the WVP of the films.

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Starch extruded in the presence of a plasticizer results in a material called thermoplastic starch (TPS). TPS mixed with poly(butylene adipate co-terephthalate) (PBAT), soybean oil (SO), and surfactant may result in films with improved mechanical properties due to greater hydrophobicity and compatibility among the polymers. This study characterized films produced from blends containing 65% TPS and 35% PBAT with SO added as compatibilizer. The Tween 80 was added to prevention of phase separation. The elongation and resistance were greater in the films with SO. The infrared spectra confirmed an increase in ester groups bonded to the PBAT and the presence of groups bonded to the starch ring, indicating TPS-SO and PBAT-SO interactions. The micrographs suggest that the films with SO were more homogenous. Thus, SO is considered to be a good compatibilizer for blends of TPS and PBAT.

Resumo: A incorporação de amido ao polímero poli (butilenoadipatoco-tereftalato) (PBAT) através de blendas com alto teor de amido pode ser uma alternativa para obter embalagens biodegradáveis, minimizar custos e o uso de recursos não renováveis. No entanto, a adição de amido aumenta a permeabilidade ao vapor de água (PVA). A incorporação em filmes com amido de substâncias como óleos vegetais e surfactantes pode diminuir a hidrofilicidade, favorecendo as aplicações destes como embalagens. A hidrofilicidade dos filmes elaborados por blendas de amido/PBAT adicionados de óleo de soja (OS) e tween 80 (TW) foi avaliada considerando o efeito do OS e TW nas isotermas de sorção dos filmes, na PVA e nos coeficientes de difusão (D w ) e solubilidade (β) do vapor de água. Filmes com OS com ou sem TW apresentaram menor quantidade de água de sorção, sendo os filmes com menores quantidades de OS e sem TW menos hidrofílicos e menos permeáveis aos vapores de água. A adição de OS reduziu os valores de β e D w dos filmes de amido/PBAT. O efeito foi relacionado com o aumento das porções hidrofóbicas e da compatibilidade entre o amido e PBAT na presença de OS. Palavras-chave: Polímeros biodegradáveis, extrusão de sopro, blendas. Hydrophilicity of Starch and Poly(Butylene Adipate-Co-Terephthalate) (Pbat) Films Containing Tween 80 and Soybean OilAbstract: Incorporating starch into the poly(butylene adipate-co-terephthalate) (PBAT) polymer by means of blends with high starch contents is a possible option for producing biodegradable packaging using renewable resources and reducing costs. However, the addition of starch increases the water vapour permeability (WVP). The incorporation of substances as lipids and surfactants can reduce the hydrophilicity of films containing starch, favouring their use as packaging. The hydrophilicity of films produced from blends of starch/PBAT with added soybean oil (SO) and tween 80 (TW) was studied. The effects of these substances on the sorption isotherm, on the WVP and on the water vapour diffusion (D w ) and solubility (β) coefficients of the films were evaluated. The water sorption in films with SO, with or without TW, was low. The films with the lowest amount of SO and without TW were the least hydrophilic and less permeable to water vapour. Adding SO reduced the β and D w values of the starch/PBAT films. This effect was related to the increase in the hydrophobic portions and the compatibility between starch and PBAT in the presence of SO.

Mixtures of starch and other polymers have been used to produce biodegradable materials with low‐cost and enhanced properties. In this study, films containing starch mixed with alginate (ALG) and/or polyvinyl alcohol (PVOH) were characterized. Films produced using binary starch–alginate mixtures (F3, F5, and F9) had the highest tensile strength (19–28 MPa) and elongation capacity (22–17%). However, films produced using ternary starch–alginate–PVOH mixtures (F8 and F9) exhibited the best water‐barrier efficacy, with lower water‐vapor permeability (WVP) values (5 × 10 and 5.56 × 10−13 g/s/Pa/m1, respectively) than that of the starch films (23.60 × 10−13 g/s/Pa) and diffusion coefficient (Dw) values approximately seven times lower than that of films produced solely with starch. The results of the infrared analyses showed a decrease in the band representing OH stretching in films created using ternary starch–alginate–PVOH mixtures, suggesting interaction between the polymers. The films containing starch mixed with ALG and PVOH showed low monolayer. The results indicated that ternary blends created better physical barriers to the passage of water vapor and diminished the availability of active sites for water binding. The optimal proportions were found to be 80% starch, 11.4% ALG and 8.6% PVOH.