Does the Addition of Cellulosic Micro/nanobrils Improve the Properties of Hydroxypropyl Methylcellulose Films?

17 Damages to ecosystems, due to the consumption of petroleum-based materials, can be mitigated with the use of 18 biopolymers such as cellulose derivatives. The objective was to evaluate the influence of different proportions of 19 cellulose micro/nanofibrils (MFC/NFC) on the properties of hydroxypropyl methyl cellulose (HPMC) films. Films 20 were prepared using proportions of 0, 25, 50, 75 and 100% (w/w) of MFC/NFC of Pinus sp. in relation to HPMC. 21 The physical, barrier, surface, optical, morphological and mechanical properties were evaluated. Data were 22 analyzed with descriptive statistics, linear regression, principal component analysis and Pearson correlation. Solids 23 content, basis weight and density values increased with higher MFC/NFC amount, while thickness and porosity 24 were reduced. SEM images showed that films with more than 50% MFC/NFC had a more granular surface 25 resulting in reduction of transparency from 80 to 65%. The water vapor penetration did not differ between films 26 and the degradation in water was reduced from 40 to 5% as MFC/NFC was added. There were no differences for 27 contact angle and wettability, but all films showed high resistance to fat penetration. Films with MFC/NFC 28 contents between 75 and 100% showed higher values for tensile strength (50 to 65 MPa) and Young's modulus (6 29 to 10 MPa) and lower elongation at break (1 to 2%). The experimental results indicated that films with MFC/NFC 30 contents above 50% have potential to be used as packaging material. 31


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The consumption of non-renewable polymers has raised concerns about environmental damage to  In this context, the use of cellulosic nanofibrils as bionanocomposites reinforcement has been object of 57 frequent study. Krishnadev et al. (2021) studied HPMC films reinforced with 1% (m/v) of MFC/NFC and obtained 58 increase in order of 30% in tensile strength and Young's modulus. However, the transparency was reduced from 59 74 to 32% and water vapor permeability was reduced around 40%. Similarly, Hassan et al. (2018) added cellulosic 60 nanofibrils contents ranging from 10 to 75% in HPMC matrices, achieving a linear increase on films mechanical 61 strength. Additionally, the mentioned authors observed a reduction in water vapor permeability of around 30%.

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These results show that MFC/NFC is a class of material that may improve the barrier, mechanical and 63 thermal properties of bionanocomposites compared to conventional composites and materials produced from pure 64 polymers, making them a promising option to be used as biopolymer-based packaging materials (Lindström and

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The HPMC suspension was prepared by adapting the hot/cold technique described by Bilbao-Sainz 95 (2011). HPMC (11.05 g) was mixed to 0.5 L of distilled water under mechanical stirring at 90 °C and 500 rpm for 96 30 min. Subsequently, the mixture was removed from heating and 0.5 L of distilled water (25 °C) was added, being 97 the new suspension stirred for 20 min at 500 rpm. The final suspension was obtained in concentration of 1% (w/w).

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Preparation of the films 100 Complementary proportions of 25%/75%, 50%/50% and 75%/25% between MFC/NFC and HPMC were 101 mixed, according to the dry mass of each filmogenic suspension. Pure films of HPMC and MFC/NFC were also 102 produced. Each mixture was homogeneized by mechanical stirring for 30 min at 500 rpm. The films were prepared 103 by solvent evaporation from the suspensions (casting), according to the methodology described in Prado et al.

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(2017). Four films of each composition were produced, with 40 g of each filmogenic suspension poured into acrylic 105 plates with 14 cm of diameter. The plates were kept in environment with temperature of 25 °C and 60% of relative 106 humidity until total solvent evaporation.  126 Where: d = density of the films (g/cm³), ρc = density of the cellulose (≅1,54 g/cm³

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The grease resistance test was conducted according to TAPPI T 559 cm-12 (TAPPI 2012). Ten samples

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Based on this, it is possible to infer that the MFC/NFC morphology favors its dispersion in polymeric 220 matrices during the composites production. However, agglomeration of these structures may occur, as seen in The films were easily detached from the acrylic plates, presenting a homogeneous and malleable aspect.

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For all physical properties evaluated, the effect of several MFC/NFC contents was observed and all variables 230 followed a quadratic trend in the regression models adjusted (Fig. 2).

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The solids content ranged between 84 and 99%, being the highest values observed for the films with 50 232 and 100% MFC/NFC (Fig 2a). The films with other MFC/NFC contents obtained similar standard deviation 233 ranges, except for the film composed of 100% HPMC, which showed the lowest solids content (~92%).    Films with 75% of MFC/NFC showed more prominent granularity (Fig. 4g). This composition presented 301 organization in layers, with some pores and nanofibril aggregates along the film profile, indicating a heterogeneous 302 distribution of material (Fig. 4h). Films composed only of MFC/NFC also presented surface irregularity (greater 303 granularity) and discontinuous layers (Figs. 4i and 4j). The presence of HPMC between 25 and 50% in the films

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Observing the general films appearance and the cracks absence, it can be said that there was high

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Transparency of the films

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The variation of films transparency fit the quadratic model (Fig. 5). It was observed that up to 50% 318 MFC/NFC, the averages of transparencies were similar, being reduced from 81 to 63% for higher contents.

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Another parameter that influences the film transparency is cellulose crystalline structure (Zheng et al.

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On the other hand, with higher MFC/NFC contents in the HPMC matrix, formation of interfibrillary hydrogen          Correlogram for Pearson correlation between physical, optical, barrier and mechanical properties of HPMC lms reinforced with different MFC/NFC contents