Glycerol-plasticized Films Research Articles

Development and characterization of camel gelatin films: Influence of camel bone age and glycerol or sorbitol on film properties

This study developed and evaluated camel bone gelatin films (CBGFs) with glycerol or sorbitol as plasticizers. Gelatin extracted from the bones of camels (Camelus dromedarius) at ages ranging from 2.5 to 7 years was used. A comprehensive analysis was conducted, evaluating a range of properties including thickness, moisture sorption capacity, water vapor permeability (WVP), infrared spectral characteristics, light absorption behavior, solubility, as well as mechanical and thermal attributes. This thorough examination allowed for a nuanced understanding of the diverse characteristics exhibited by the camel gelatin samples across different age groups. The results indicated that camel age, glycerol, and sorbitol had a significant impact on the properties of the film (P < 0.05). Tensile strength ranged from 0.32 MPa to 3.99 MPa, while the percentage of elongation at break varied from 89.42 % to 2.68 %. Film color (lightness, L) ranged from 21.39 to 41.33. Glycerol and sorbitol plasticized films were 100 % water soluble. Moisture sorption increased with temperature (25 °C, 35 °C, and 45 °C), with sorbitol films retaining less water. WVP was low in films from old camel bones and high in glycerol-plasticized CBGF-2.5Y and CBGF-4.5Y. Thermal analysis showed a melting temperature between 158.60 °C and 174.10 °C, depending on bone age and plasticizer. These films demonstrate promise for use in food packaging, coatings, and pharmaceutical applications.

The effects of plasticizers on the mechanical properties and chemical composition of a gelatin biopolymer

Every day, oil-based plastics are manufactured, consumed, and discarded without a second thought. To combat plastic pollution, we decided to investigate gelatin bioplastics. We analysed the effects of the increasing concentration of polyethylene glycol (PEG) and glycerol plasticizers on the mechanical properties and chemical composition of the gelatin bioplastic matrix through a series of experiments. In the first experiment, we determined their tensile strength (TS) and the elongation at break (EAB) through tensile testing. We hypothesised that increasing concentrations of the plasticizers would decrease TS and increase EAB. In the second experiment, we studied their O–H bonds by Fourier-transform infrared spectroscopy analysis (FTIR). Our second hypothesis maintained that the number of O–H bonds would increase because plasticizers disrupt polymer-polymer and polymer-water hydrogen bonds. For the mechanical properties, we observed that when the concentration of PEG and glycerol plasticizers increased so too did EAB. The rising concentrations of glycerol led to a decreasing trend with TS, whereas PEG showed an increasing trend. The FTIR spectrum revealed that a high abundance of O–H bonds was present at the strong and broad absorption peak of 3400 cm-1, with the pure gelatin films having the highest absorption, followed by glycerol-plasticized films and PEG-plasticized films having the least absorption. We concluded that 3% w/v PEG film outperformed other PEG films and 3% w/v glycerol films. The cytotoxicity results showed that all films had a cell viability above the threshold of 75% and hence food-safe.

Development of Dry Walnut Shell Edible Film Plasticized with Glycerol and/or Sorbitol and Incorporated with Aloe Vera Gel and Lemon Essential Oil

Edible packaging films produced from biomaterials are environmentally friendly, promising alternatives against synthetic plastics films. The aim of this study was to produce a low-cost edible film from waste dry walnut shell by casting method. Effects of the plasticizer type and concentration, lemon essential oil (LEO) and aloe vera gel (AVG) addition on edible films properties were investigated. Produced edible films characterization analysis were realized by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). Moisture content, water vapor transmission rate (WVTR), water solubility, swelling index, thicknesses and color parameters of the produced edible films were investigated. Moisture content of the films was decreased between 23.3–50.6% after LEO and AVG addition, except the moisture content of the film plasticized with 20% sorbitol was increased by 518%. WVTR of the films were increased between 8.7–72.3% after LEO and AVG addition due to the hydrophobic character of LEO. Glycerol plasticized edible films water solubility were decreased between 27.3–75.9%, sorbitol plasticized edible films water solubility were increased between 237.5–100.8% with LEO and AVG incorporation. The swelling index of C1 was reduced by 51.5%, C2 was reduced by 62.4%, C4 was reduced by 36.1%. The swelling index of the C3 was increased by 10.5%, C5 was increased by 21.5%. LEO and AVG addition increased to the film thickness maximum 79.2%. Total color changes (ΔE) of glycerol plasticized films were higher than sorbitol plasticized film. The edible film produced can be used in food packaging due to the appropriate physical and barrier properties.

Physicochemical and structural properties of a bio-based antioxidant packaging film derived from Eremurus luteus root gum

A novel bio-based film from Eremurus luteus root gum (ELRG), as a new source of glucomannans, was fabricated and the effects of two plasticizers (glycerol and sorbitol) and their concentration (30, 40, and 50% w/w) on some physical, optical, barrier, antioxidant and mechanical properties, and microstructure of the films were investigated. The results demonstrated that the increase in the plasticizers’ concentration from 30% to 50% (w/w) increased the moisture content, solubility, and water vapor permeability (WVP) but decreased the contact angle of the ELRG films. The maximum antioxidant activity of the films was obtained by the addition of 50% of glycerol or sorbitol. The plasticized films by different concentrations of glycerol exhibited more extensibility and lower tensile strength in comparison with sorbitol films. The color analysis revealed that increasing both plasticizers’ concentrations caused the L value to increase while the ΔE value decreased. The more transparency and light transmission were observed for the sorbitol films. The SEM images indicated smooth and uniform surface morphology without cracks of plasticized films compared with the unplasticized film. The results of the present study suggest that ELRG is a good source to fabricate bio-based films for the food products packaging or carrying bioactive components. • ELRG introduced as a new biomaterial source for an antioxidant film fabrication. • Influence of plasticizer type and concentration was investigated. • Physical, barrier, and mechanical properties, and microstructure were determined. • Glycerol indicated greater efficiency than sorbitol in plasticizing ELRG films. • The glycerol plasticized films showed more antioxidant activity.

Argan (Argania spinosa L.) Seed Oil Cake as a Potential Source of Protein-Based Film Matrix for Pharmaco-Cosmetic Applications.

Various different agri-food biomasses might be turned into renewable sources for producing biodegradable and edible plastics, potentially attractive for food, agricultural and cosmeceutical sectors. In this regard, different seeds utilized for edible and non-edible oil extraction give rise to high amounts of organic by-products, known as seed oil cakes (SOCs), potentially able to become protein-rich resources useful for the manufacturing of biodegradable films. This study reports the potential of SOC derived from Argania spinosa (argan), a well-known plant containing valuable non-refined oil suitable for food or cosmetic use, to be a promising valuable source for production of a protein-based matrix of biomaterials to be used in the pharmaco-cosmetic sector. Thus, glycerol-plasticized films were prepared by casting and drying using different amounts of argan seed protein concentrate, in the presence of increasing glycerol concentrations, and characterized for their morphological, mechanical, barrier, and hydrophilicity properties. In addition, their antioxidant activity and effects on cell viability and wound healing were investigated. The hydrophobic nature of the argan protein-based films, and their satisfying physicochemical and biological properties, suggest a biorefinery approach for the recycling of argan SOC as valuable raw material for manufacturing new products to be used in the cosmeceutical and food industries.

Plasticizing effect of Apis mellifera honey on whey protein isolate films.

The aims of this study were to analyze the plasticizing effect of Apis mellifera honey on the mechanical, physicochemical and optical properties of whey protein isolate (WPI) films and to compare the results collected with the plasticizing effect of glycerol on WPI-films. Response surface was applied to optimize the amounts of WPI and glycerol in order to obtain films with higher tensile strength (TS), moderate elongation, and lower water vapor permeability so that they could be used as reference films. Honey was added at different concentrations (60%, 80%, and 100%) of g honey/100 g WPI, as a plasticizer to the WPI-films. In comparison to glycerol-plasticized films, an increase in the percentage of honey produced a reduction of 20 ± 10 to 48 ± 0.5% of TS, a 66± 0.5% lower in Young's modulus (WPI-films with 100% honey), and an increase of 186± 11% in elongation at break in the WPI-films with 100% honey. Honey-plasticized WPI-films were from 29± 11 to 43± 3% less permeable to water vapor than glycerol-plasticized WPI films. The mechanical characteristics of the 80% honey formulation did not differ significantly from those of the reference film (p > 0.05). Findings from this study indicate that honey has great potential as a plasticizer in WPI-films.

Comparative Effect of Different Plasticizers on Barrier, Mechanical, Optical, and Sorption Properties of Hydroxypropyl Methylcellulose (HPMC)–Based Edible Film

Identifying ideal plasticizer is pivotal to develop a biopolymer-based edible films for food packaging. The effect of different plasticizers (glycerol, polyethylene glycol, sorbitol) on the mechanical, water vapor barrier, optical, and moisture sorption properties of hydroxypropyl methylcellulose (HPMC) -based flexible films was examined in this study. Mechanical properties and water vapor permeability (WVP) of films were determined using standard ASTM methods. Moisture sorption isotherm (MSI) for different HPMC films were obtained thermogravemitically and seven sorption models were fitted to experimental sorption data through nonlinear regression using curve fitting tool in MATLAB R2015b and goodness of fit of these models was compared based on Akaike information criterion (AIC). GAB model was used to determine the monolayer moisture content and heat of sorption of different films. Plasticizing efficacy of different plasticizers was significantly different for HPMC film in studied concentration range. Water vapor permeability (WVP) for native HPMC film was 0.451 g mm/kPa m2 h, which further increased to 0.972, 0.890, and 0.615 g mm/kPa m2 h when 25% (w/w of HPMC) glycerol, PEG, and sorbitol were added as plasticizers, respectively. GAB model showed an increase in monolayer moisture (M0) content with increasing plasticizer concentration and the highest M0 value was observed for glycerol-plasticized film. Added plasticizers were found to be effective in providing desirable flexibility in terms of elongation to HPMC film which is beneficial for coating and shrink wrap packaging application but adversely affect the tensile strength and transparency of film. Henderson and Oswin models were selected as the best fit model to the experimental sorption data based on AIC values. The findings from the current study would serve in selection of suitable plasticizer for HPMC-based film/coating in food packaging applications.

Effect of plasticizers on the properties of sugar palm nanocellulose/cinnamon essential oil reinforced starch bionanocomposite films

Abstract This work examines the effects of plasticizer type and concentration on mechanical, physical, and antibacterial characteristics of sugar palm nanocellulose/sugar palm starch (SPS)/cinnamon essential oil bionanocomposite films. In this research, the preparation of SPS films were conducted using glycerol (G), sorbitol (S), and their blend (GS) as plasticizers at ratios of 1.5, 3.0, and 4.5 wt%. The bionanocomposite films were developed by the solution casting method. Plasticizer Plasticizers were added to the SPS film-forming solutions to help overcome the fragile and brittle nature of the unplasticized SPS films. Increasing plasticizer contents resulted in an increase in film thickness and moisture contents. On the contrary, the increase in plasticizer concentrations resulted in the decrease of the densities of the plasticized films. The increase in the plasticizer content from 1.5 to 4.5% revealed less influence towards the moisture content of S-plasticised films. For glycerol and glycerol-sorbitol plasticized (G and GS) films, higher moisture content was observed compared to S-plasticised films. Various plasticizer types did not significantly modify the antibacterial activity of bionanocomposite films. The findings of this study showed significant improvement in the properties of bionanocomposite films with different types and concentrations of plasticizers and their potential for food packaging applications was enhanced.

Study of the effect of the addition of plasticizers on the physical properties of biodegradable films based on kefiran for potential application as food packaging

Spectroscopies analysis indicated that kefiran contains branched hexasaccharide repeating units. Neat kefiran films, 2 and 5% w/w of glycerol, d-glucitol, d-galactitol, d-mannitol, and d-limonene were incorporated as plasticizers. Neat and plasticized kefiran films were characterized by physical, thermal, mechanical, optical, and water solubilization properties. Neat kefiran had a glass transition temperature (Tg) of −20 ± 2 °C and, with the addition of plasticizers between −15 to −17 ± 2 °C. The values were close to the neat kefiran, and the results could be attributed to a lower amount of plasticizer used. The solubility of the glycerol plasticized films increases by 33% and decreased with the concentration of other plasticizers in comparison with the neat kefiran. d-glucitol and d-galactitol decreased the microhardness and Young’s Modulus of films around 30% and 74% respectively, obtaining more flexible kefiran films. Kefiran based films could find applications as potential materials in the food-packaging industry.

Films Fabricated with Native and Ball‐Milled Modified Glutinous Rice Starch: Physicochemical and Mucoadhesive Properties

AbstractThis study aims to investigate the physicochemical and mucoadhesive properties of films made of glutinous rice starch (GRS), native (NGRS), and ball‐milled modified GRS (MGRS), in comparison with the reference mucoadhesive polymers. By using the solvent casting technique with glycerol (30% w/w of starch mass) as a plasticizer, all GRS films exhibit satisfactory and comparable thickness and weight uniformity, surface pH, and moisture content. ATR‐FTIR indicates that the hydrogen bonds are formed between GRS and glycerol. The absence of crystalline structure of GRS in glycerol plasticized films is confirmed using ATR‐FTIR and XRD. The films made of NGRS and MGRS have similar swelling behavior (751 ± 75 to 1002 ± 104%), whereas those made of longer milling time MGRS demonstrate higher erosion (27.1 ± 4.2%) (p &lt; 0.05). MGRS films exhibit greater flexibility with lower tensile strength (9.6 ± 1.7 to 9.8 ± 1.0 MPa) but higher elongation (162.5 ± 6.5 to 165.7 ± 2.5%) compared to native systems (13.7 ± 0.5 MPa and 128.1 ± 5.0%, respectively) (p &lt; 0.05). The MGRS films show comparable mucoadhesiveness expressed as detachment force and work of adhesion to those of sodium carboxymethylcellulose, but higher than those of NGRS, hydroxypropyl methylcellulose, and chitosan (p &lt; 0.05). This study reveals the potential exploitation of GRS as a mucoadhesive film former for pharmaceutical application.

Effects of plasticizers on water sorption and aging stability of whey protein/carboxy methyl cellulose films

Influence of water sorption and phase transitions requires clarification to understand plasticizer mechanisms on the physico-chemical properties of biodegradable and edible films. The effects of plasticizers as glycerol, xylitol, sorbitol, polyethylene glycol 400 (PEG 400) and oleic acid were investigated on water sorption, phase transitions and properties in whey protein concentrate and carboxy methyl cellulose blend films (WPC-CMC). Stability after aging at different humidity (50% RH and 75% RH for 30 days) was determined. Sorption isotherms of glycerol-plasticized films showed the highest water affinity and binding sites led to the lowest glass transition temperature (Tg). Xylitol showed similar water sorption behavior to sorbitol but higher plasticization effect. An increased C-atom of glycerol, xylitol and sorbitol gave identical infrared spectra. Conversely, oleic acid modified protein secondary structures contributed to the lowest water sorption and highest Tg as indicated by amide I and amide II bands in the infrared spectra. Highly hydrophilic plasticizers as glycerol, xylitol and sorbitol showed less sensitivity to water-induced Tg reduction. Water sorption greatly improved plasticization effects in PEG 400 and oleic acid which contained non-polar components. Aging accelerated the Maillard reaction in WPC-CMC and led to physico-chemical changes and destabilized films. Light transmission decreased concurrently with increased brown pigments that improved the water barrier and stiffness. Higher humidity accelerated molecular mobility and facilitated physico-chemical changes of the polymer blends. Oleic acid showed the least stability during aging, while sorbitol greatly enhanced water barrier properties and stability of the blend films. Molecular structures of plasticizer greatly influenced water sorption, modified molecular orientation of biopolymers which subsequently impacted properties and stability of the films.

Plasticized hemicelluloses/chitosan-based edible films reinforced by cellulose nanofiber with enhanced mechanical properties

In this work, the properties of the plasticized hemicelluloses/chitosan-based edible films reinforced by cellulose nanofiber (CNF) have been evaluated. Results showed that the tensile strength (TS) of the film increased by 2.3 times with adding 5% CNF. As compared with unplasticized film, the films containing 10–40% plasticizers (glycerol, xylitol, sorbitol) showed slightly higher water vapor permeability, oxygen permeability, transparency, solubility, and lower contact angle. Among the three types of plasticized films, glycerol-plasticized films exhibited the highest tensile strain at break (TB, 7.80–18.53%), while the sorbitol-plasticized films exhibited the highest TS (23.14–48.96 MPa). However, there were no substantial differences in the three types of plasticized films except TS and TB. Overall, the films containing 20–30% glycerol with high TS (31.02–38.56 MPa) and TB (10.07–15.98%) were suitable for food-packaging applications where high mechanical strength and flexibility are required.

Antimicrobial packaging based on a LAE containing zein coating to control foodborne pathogens in chicken soup

In this study, zein coatings containing Lauroyl-l-arginine ethyl ester monohydrochloride (LAE) were developed to be applied on polypropylene films and manufacture an active food packaging. The concentration of LAE and the addition of a suitable plasticizer (glycerol or oleic acid (OA)) were the main variables considered. Active plasticized zein films, with glycerol or oleic acid were characterized in terms of release kinetics, mechanical, barrier, optical, and antimicrobial properties. Results showed that active agent concentration, (5 and 10%), had no-significant effect on mechanical and WVP properties of the plasticized films. Films plasticized with OA presented greater water resistance, UV-light opacity, and water barrier properties than glycerol-plasticized films. On the contrary, the latter had better antimicrobial properties. The analysis of LAE release kinetics from films to different food simulants revealed different behaviours, depending on both film formulation and food simulant. Despite the lower water resistance of coatings containing glycerol, bags based on polypropylene/glycerol plasticized zein containing 10% of LAE presented a great antimicrobial activity in tests with chicken soup (real food system) contaminated with pathogen bacteria, concretely, the films showed 3.21 Log reduction against Listeria monocytogenes and 3.07 log reductions against Escherichia coli. These results suggest a promising strategy on the use of LAE-containing zein in active food packaging to control foodborne pathogens.

Development and characterization of novel composite glycerol-plasticized films based on sodium caseinate and lipid fraction of tomato pomace by-product

Tomato processing industries generate many byproducts that are mainly unexploited or underutilized. In order to convert tomato byproducts into added-value products, composite films made of sodium caseinate (NaCas), glycerol (25 wt%), and lipidic fraction of tomato pomace (LFTP) at different contents (0–40 wt%) were produced and characterized in terms of thermal stability, antioxidant activities, mechanical, hydrodynamic and optical properties. Our results showed that increasing LFTP concentration beyond 20 wt% increased the flexibility of NaCas films within the range of 17–25%. Moreover, LFTP incorporation at the highest content improved thermal stability of NaCas films and reduced their water absorption by >72%. Furthermore, increasing LFTP content led to a significant decrease in the light transmission of NaCas/LFTP composite films. Such improvement in functional and physical properties can be attributed not only to the establishment of specific interactions between NaCas and LFTP but also to their good miscibility in the blend along with the homogeneous dispersion of the incorporated LFTP in the polymeric matrix, as confirmed by FTIR and SEM analysis. On the other hand, the antioxidant capacity of NaCas/LFTP composite films was enhanced by increasing LFTP content most likely due to LFTP's high total phenolics content.

Glycerol-Plasticized Films Obtained from Whey Proteins Denatured at Alkaline pH

Whey represents the major by-product of cheese industry. One possibility to recycle the whey wastes is the use of their globular proteins as a polymer source for the production of biodegradable plastic materials. Whey protein (WP)-based films are usually obtained by protein heat treatment in the presence of glycerol (GLY) as plasticizer at pH 7, a method which would require commercially high costing process. In this work we explored the possibility of producing manageable whey-derived materials without any heat-treatment but under alkaline conditions. The reported results demonstrated that the casting at pH 12 of the unheated WP film forming solutions (FFSs), containing either 40% or 50% GLY, led to produce more resistant and flexible materials than the ones obtained at pH 7. Film opacity was observed significantly increased, being higher in the samples obtained at alkaline pH without WP heating and with higher GLY concentrations. Finally, moisture content decreased with the reduction of GLY content, both in heated and unheated WP-based films, whereas water uptake of the different films prepared at pH 12 did not significantly change.

Antioxidant films from mango kernel components

Different compounds were sequentially extracted from mango seed kernels, namely, mango kernel fat (MKF), a phenolic extract (MKPE), and starch (MKS), with yields of about 11%, 17%, and 39% respectively. The main fatty acids in MKF were oleic and stearic. Gallic acid and its derivatives were the predominant phenolics in MKPE. Glycerol-plasticized films were prepared with different weight proportions of MKS (80–100%), MKF (0–20%), and MKPE (0–20%). The presence of fats and phenolics presented plasticizing effects on the starch films, although their elongation has sharply decreased when the MKF content increased from 10 to 20%, probably because of the high saturation of MKF. MKPE was more effective than MKF in decreasing water vapor permeability. Moreover, the phenolics imparted the films with active (antioxidant and UV absorbing) properties, although they also decreased the visible light transparency of films.

Mechanical and thermal properties of tapioca starch films plasticized with glycerol and sorbitol

Recently, the use of natural polymer such as starch to produce packaging film has received much attention as a substitute for conventional petroleum-based packaging film since starch is biodegradable and sustainable. However, the poor characteristic of starch such as high brittleness will limit the application of the film. This problem can be solved by adding plasticizers. In this work, the effects of different types of plasticizers (glycerol, sorbitol and 1:1 mixture of glycerol-sorbitol) on mechanical and thermal properties of tapioca starch films prepared by solvent casting method were investigated. The films were characterized in term of mechanical (tensile strength (TS), elongation at break (EAB), Young Modulus (YM) and thermal properties (thermo-gravimetric analysis (TGA)). Film plasticized with sorbitol exhibited higher TS and YM but lower EAB value which contributed to higher thermal stability than glycerol-plasticized film. This was due to the strong interactions between the polymer chains resulting from the high molecular weight of sorbitol. Hence, films became more rigid and thus promoted to a greater thermal resistance.

Development and properties of new chitosan-based films plasticized with spermidine and/or glycerol

Different chitosan solutions were characterized by evaluating zeta potential and particle size, in the absence or presence of spermidine and/or glycerol, and the physicochemical, morphological and antimicrobial properties of the derived films were determined. An increase of film tensile strength and elongation at break was observed by increasing chitosan amounts, whereas only tensile strength and Young's modulus values were revealed higher at all chitosan concentrations when spermidine was absent. Spermidine-containing films were always more extensible exhibiting an elongation at break even higher than that of glycerol-plasticized films. The concurrent presence of appropriate concentrations of spermidine and glycerol further enhanced the extensibility and plasticity of the biomaterial, conferring to it the ability to be heat-sealed, as well as similar permeability in comparison with Viscofan NDX, widely commercialized as protein-based food casing. Finally, all the prepared films exhibited a clear antimicrobial activity, thus representing credible candidates as food preservative coatings and/or wrappings.

Vicia villosa protein isolate: a new source of protein to make a biodegradable film

Edible films from Vicia villosa protein isolate (VVPI) containing different contents of glycerol and sorbitol (30, 40, 50 and 60%w/w of protein) were developed. The aim of this study was to investigate the influence of type and concentration of plasticizers on the properties of edible films obtained from VVPI. Type and concentration of plasticizer significantly (p &lt;0.05) affected the mechanical, barrier, thermal and surface properties as well as opacity of the films. As plasticizer concentration increased, tensile strength decreased concomitant with increase in elongation at break and water vapor permeability. The similar trend behavior was observed for the film solubility, which increased with increasing plasticizer concentration. Sorbitol plasticized films, showed higher film solubility compared to glycerol plasticized films. Sorbitol plasticized films provided the most tensile strength values; however, its effect on water vapor permeability was low. In contrast, glycerol plasticized films exhibited the least tensile strength values, resulting in increasing water vapor permeability. Opacity of glycerol plasticized films was lower than that of sorbitol plasticized films, and decreased with increasing plasticizer content (p &lt;0.05). Also, a significant decrease (p &lt;0.05) was observed in thermal features and surface hydrophobicity values with increasing in plasticizer contents. It was observed that the films plasticized with sorbitol had lower moisture content than those with glycerol.

Protein/Protein Nanocomposite Based on Whey Protein Nanofibrils in a Whey Protein Matrix

This article describes nanocomposite films with separately grown protein nanofibrils (PNFs) in a nonfibrillar protein matrix from the same protein starting material (whey). Tensile tests on the glycerol-plasticized films indicate an increased elastic modulus and a decreased extensibility with increasing content of PNFs, although the films are still ductile at the maximum PNF content (15 wt %). Infrared spectroscopy confirms that the strongly hydrogen-bonded β-sheets in the PNFs are retained in the composites. The films appear with a PNF-induced undulated upper surface. It is shown that micrometer-scale spatial variations in the glycerol distribution are not the cause of these undulations. Instead, the undulations seem to be a feature of the PNF material itself. It was also shown that, apart from plasticizing the protein film, the presence of glycerol seemed to favor to some extent exfoliation of stacked β-sheets in the proteins, as revealed by X-ray diffraction.