Extrusion of pectin/starch blends plasticized with glycerol

The microstructural and thermal dynamic mechanical properties of extruded pectin/starch/glycerol (PSG) edible and biodegradable films were measured by scanning electron microscopy (SEM) and thermal dynamic mechanical analysis (TDMA). SEM revealed that the temperature profile (TP) in the extruder and the amount of water present during extrusion could be used to control the degree to which the starch was gelatinized. TDMA revealed that moisture and TP during extrusion and by inference the amount of starch gelatinization had little effect on the mechanical properties of PSG films. Furthermore, TDMA revealed that PSG films underwent a glass transition commencing at about −50°C and two other thermal transitions above room temperature. Finally, it was concluded that the properties of extruded PSG films were comparable to those cast from solution.     

Two stage extrusion of plasticized pectin/poly(vinyl alcohol) blends

Blends of pectin with starch (high amylose and normal), poly(vinyl alcohol) (PVOH), and glycerol were extruded in a twin screw extruder, pelletized, and then further processed into blown film and extruded sheet using a single screw extruder. The samples were analyzed using tensile measurements, dynamic mechanical analysis, and scanning electron microscopy. PVOH levels of 24% or greater were necessary to successfully make blown film, while extruded sheet could be made at a level of 16% PVOH. Tensile strength and initial modulus of the extruded sheets were slightly higher in the machine direction than in the cross direction, while the reverse was true for elongation to break. For the blown films tensile strength tended to be higher in the transverse direction than in the machine direction, while the reverse was seen for initial modulus. Increased levels of PVOH led to increases in tensile strength and elongation to break, while initial modulus was decreased. Morphology as determined by SEM visually indicated stretching in the transverse direction of the blown films. The second stage extrusion appeared to promote -helix formation in the high amylose starch.     

Microstructural characterization of yam starch films

Yam starch films were produced by thermal gelatinization of starch suspensions using different starch and glycerol concentrations and were compared to control samples without glycerol. Films were characterized by polarized light microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermomechanical analysis (TMA), X-ray diffraction, water vapor permeability (WVP) and water sorption isotherms. The polarized light microscopy and DSC data showed that starch gelatinization for film formation was complete. Plasticized films have a homogeneous structure as observed by SEM. At water activities >0.43, glycerol increased the equilibrium moisture content of the films due to its hydrophilic character. X-ray pattern of the yam films could be assigned to a B-type starch; during storage this pattern remained almost the same, however a slight recrystallization process could be observed. Amylopectin retrogradation was not observed by DSC with storage time of the films. Glass transition temperatures of films with glycerol were lower than those of control films as measured by DSC and TMA. WVP of yam starch films increased with the presence of glycerol.     

Mechanical, microstructural and solubility properties of pectin/poly(vinyl alcohol) blends

Citrus pectin was blended and cast into films with poly(vinyl alcohol) (PVOH). PVOH and pectin were miscible in all proportions. Dynamic mechanical analysis revealed that pectin controls exhibited no thermal transitions, whereas PVOH controls exhibited a glass transition temperature (T_g) over a broad temperature range commencing at about 0 °C and ending about 50 °C. A mixture of 49% pectin, 21% PVOH and 30% glycerol exhibited lower storage moduli and more flexibility than comparable mixtures of either pectin/PVOH or pectin/glycerol. Scanning electron microscopy and phase contrast optical microscopy indicated that the mixture was biphasic and a compatible composite either of PVOH in pectin or pectin in PVOH depending on which macromolecule was in excess. Elongation to break measurements revealed that pectin/PVOH films underwent a brittle to ductile transition with increasing PVOH composition. The addition of glycerol to pectin/PVOH films increased ductility significantly when films were relatively brittle. Initial moduli (IM) as a function of composition gave complex curves which exhibited either one or two local maxima depending on such factors as degree of hydrolysis and molar mass of the PVOH in addition to the moisture content of the film. Solubility studies in water revealed that, at 30 and 50 °C, only films with 30% PVOH or less were soluble. At 70 °C, all compositions were soluble but films containing pectin dissolved more rapidly than those without. The solution kinetics of pectin/PVOH films with 30% or less PVOH were approximated with zero-order kinetics and activation energies were about 3–5 kcal mol⁻¹. In general, addition of PVOH to pectin films resulted in films with more PVOH-like properties and addition of pectin to PVOH films resulted in films with more pectin-like properties.     

Bioplastics from feather quill

Poultry feather quills have been extruded in a twin screw extruder with sodium sulfite treatment as a reducing agent. The effect of four different plasticizers (ethylene glycol, propylene glycol, glycerol, and diethyl tartrate) on the thermoplastic properties was then investigated. Conformational changes and plasticizer-protein interactions in the extruded resins were assessed by Fourier transform infrared spectroscopy (FTIR), while viscoelastic behavior of the quill keratin plasticized with different plasticizers was investigated by dynamic mechanical analysis (DMA). Differential scanning calorimetry (DSC) was used to determine the effect of different plasticizers on protein denaturation. Thermal degradation patterns of the extrudates were studied by thermogravimetric analysis (TGA). The effect of plasticizers on the mechanical properties of resins was also assessed by tensile strength measurements. Results indicated that ethylene glycol was able to interact more effectively with quill keratin at the molecular level, exhibiting only one sharp glass transition, better mechanical properties, and higher transparency compared to other plasticized resins. The two phases found in glycerol plasticized material were attributed to glycerol-rich and protein-rich zones. Propylene glycol and diethyl tartrate exhibited lower H-bonding interactions and showed wide transition regions in DMA profiles during heating, suggesting weak and heterogeneous interactions between quill keratin and these plasticizers.     

Cassava bagasse cellulose nanofibrils reinforced thermoplastic cassava starch

Cellulose cassava bagasse nanofibrils (CBN) were directly extracted from a by-product of the cassava starch (CS) industry, viz. the cassava bagasse (CB). The morphological structure of the ensuing nanoparticles was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), presence of other components such as sugars by high performance liquid chromatography (HPLC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) experiments. The resulting nanofibrils display a relatively low crystallinity and were found to be around 2–11 nm thick and 360–1700 nm long. These nanofibrils were used as reinforcing nanoparticles in a thermoplastic cassava starch matrix plasticized using either glycerol or a mixture of glycerol/sorbitol (1:1) as plasticizer. Nanocomposite films were prepared by a melting process. The reinforcing effect of the filler evaluated by dynamical mechanical tests (DMA) and tensile tests was found to depend on the nature of the plasticizer employed. Thus, for the glycerol-plasticized matrix-based composites, it was limited especially due to additional plasticization by sugars originating from starch hydrolysis during the acid extraction. This effect was evidenced by the reduction of glass vitreous temperature of starch after the incorporation of nanofibrils in TPSG and by the increase of elongation at break in tensile test. On the other hand, for glycerol/sorbitol plasticized nanocomposites the transcrystallization of amylopectin in nanofibrils surface hindered good performances of CBN as reinforcing agent for thermoplastic cassava starch. The incorporation of cassava bagasse cellulose nanofibrils in the thermoplastic starch matrices has resulted in a decrease of its hydrophilic character especially for glycerol plasticized sample.     

Complexation of amidated pectin with poly(itaconic acid) as a polycarboxylic polymer model compound

Complexes based on amidated pectin (AP) and poly(itaconic acid) (PIA) were prepared by casting films from solutions of AP and PIA in different ratios with the pectin amount ranging from 10% to 90% by mass. The complexes were investigated by elemental analysis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetry (TG). In all investigated ratios of AP/PIA glassy transparent films with a uniform structure were obtained. The results of elemental analysis confirmed the composition of the complexes, and FTIR spectroscopy has shown carboxylic and amide peak shifting, indicating complex formation between AP and PIA. Comparison of thermograms of AP/PIA films with different ratios of AP indicated that the increase of the amount of AP increases the thermal stability of the films by retarding the onset of the main degradation processes.     

Alginate and pectin composite films crosslinked with Ca ions: Effect of the plasticizer concentration

The manufacture of composite biofilms of alginate and LM-pectin crosslinked with calcium ions requires a two-step contact with Ca²⁺: initially a low-structured pre-film is formatted which is further crosslinked in a second contact with a more concentrated Ca²⁺ solution containing plasticizer. This research evaluated the influence of the plasticizer (glycerol) concentration (1–15% w/v) in this finishing reticulation step on final films characteristics. The results indicated that the extent of the simultaneous Ca²⁺ crosslinking and plasticization with glycerol was determined by the level of structural organization obtained in the pre-reticulation. Increasing the glycerol concentration of the crosslinking solution increased film solubility in water, moisture content, volumetric swelling and flexibility and decreased the resistance to tensile stress. Transparent alginate and pectin composite films with acceptable mechanical properties, low solubility and limited degree of swelling were obtained with 10% glycerol in the second contact solution.     

Material properties of concentrated pectin networks

We have examined the mechanical behaviour of different types of pectin at high concentrations (> 30% w/w), relevant to the behaviour of pectin in the plant cell wall, and as a film-forming agent. Mechanical properties were examined as a function of counterion type (K(+), Ca(2+), Mg(2+)), concentration and extent of hydration. Hydration was controlled in an osmotic stress experiment where pectin films were exposed to concentrated polyethylene glycol [PEG] solutions of known osmotic pressure. We investigated the mechanical behaviour under simple extension. The results show that the swelling and stiffness of the films are strongly dependent on pectin source and ionic environment. At a fixed osmotic stress, both Ca(2+) or Mg(2+) counterions reduce swelling and increase the stiffness of the film.     

Influence of amylose content on starch films and foams

After extraction of smooth pea starch and waxy maize starch from pure amylose and amylopectin fractions, films with various amylose contents were prepared by casting in the presence of water or water with glycerol. For unplasticized films, a continuous increase in tensile strength (40–70 MPa) and elongation (4–6%) was observed as amylose increased from 0 to 100%. Discrepancies with values obtained for native starches with variable amylose content and different botanical origins were attributable to variations in the molecular weights of components. Taking cell wall properties into account, the values obtained in the laboratory were used to improve the relation between the flexural behavior of extruded foams and the model of cellular solids with open cavities.

The properties of plasticized films were not improved by the presence of glycerol and remained constant when amylose content was higher than 40%. Results are interpreted on the basis of topological differences between amylose and amylopectin.     

Effect of glycerol on behaviour of amylose and amylopectin films

The effect of water and glycerol on sorption and calorimetric T_gs of amylose and amylopectin films were examined. The mechanical properties of the films were also analysed under varying glycerol content at constant RH and temperature. Based on changes observed in sorption and tensile failure behaviour glycerol was strongly interacted with both starch polymers. Even though water was observed to be more efficient plasticiser than glycerol, glycerol also affected the T_g. But in spite of the observed decrease in T_g under low glycerol contents brittleness of the films increased based on changes in elongation. The increase in brittleness of both polymers was also in agreement with their actual behaviour. At around 20% glycerol great change in the rheological properties occurred. Above 20% glycerol amylose film showed much larger elongation than the low glycerol content films and was still strong but the amylopectin produced a very week and non-flexible film.     

Mechanical and water barrier properties of starch/PVA composite films by adding nano-sized poly(methyl methacrylate-co-acrylamide) particles

The aim of this work is to prepare starch/PVA composite films added nano-sized poly(methyl methacrylate-co-acrylamide) (PMMA-co-AAm) particles and to investigate the mechanical properties, water barrier properties, and soil burial degradation for the films. Composite films were prepared by using corn starch, polyvinyl alcohol (PVA), nano-sized PMMA-co-AAm particles, and additives, i.e., glycerol (GL), xylitol (XL), and citric acid (CA). Nano-sized PMMA-co-AAm particles were synthesized by emulsion polymerization. The results of the evaluation of properties for prepared films indicated that compared with films without PMMA-co-AAm particles, the mechanical properties and water resistance were improved up to 70-400% by the addition of nano-sized PMMA-co-AAm. In addition, the results of the soil burial biodegradation revealed that films added PMMA-co-AAm particles were degraded by about 45-65% after 165 days.     

Compression molding and tensile properties of thermoplastic potato starch materials

The mechanical and melt flow properties of two thermoplastic potato starch materials with different amylose contents were evaluated. The materials were prepared by mixing starch, glycerol, and water, mainly in the weight proportions of 10:3:4.5. Compression molding was used to produce sheets/films with a thickness in the range of 0.3-1 mm. After conditioning at 53% relative humidity (RH) and 23 C, the glycerol-plasticized sheets with a higher amylose content (HAP) were stronger and stiffer than the normal thermoplastic starch (NPS) with an amylose content typical for common potato starch. The tensile modulus at 53% RH was about 160 MPa for the high-amylose material and about 120 MPa for the plasticized NPS. The strain at break was about 50% for both materials. The stress at break was substantially higher for the HAP materials than for the NPS materials, 9.8 and 4.7 MPa, respectively. Capillary viscometry at 140 C showed that the high-amylose material had a higher melt viscosity and was more shear-thinning than the NPS. Dynamic mechanical measurements indicated a broad transition temperature range for both types of starch material. The main transition peaks for glycerol-plasticized starch were located at about room temperature with the transition for the HAP material being at a somewhat higher temperature than that of the NPS material with a lower amylose content. It was also noted that the processing conditions used during the compression molding markedly affected the mechanical properties of the starch material.     

Effects of extrusion and glycerol content on properties of oxidized and acetylated corn starch-based films

Oxidized and acetylated corn starch-based films were prepared by casting with glycerol as a plasticizer. The present study investigated the effects of extrusion prior to film-making and glycerol content on the properties of starch films. The films with extrusion exhibited lower tensile strength, higher elongation at break, higher water vapor permeability and higher oil permeability than those without extrusion. Extrusion reduced heat sealability of the films. With the increase of glycerol content, the films became more flexible with higher elongation at break and lower tensile strength. Water vapor permeability, oil permeability and the range between the onset temperature and the melt peak temperature rose as glycerol content increased. The thermograms indicated that plasticizers and biopolymers were compatible. These results suggested that extrusion did no good to starch films while glycerol content had apparent effect on the mechanical and barrier properties of the films.     

Structural characterization and properties of starch/konjac glucomannan blend films

In this work, a series of glycerol-plasticized pea starch/konjac glucomannan (ST/KGM) blend films was prepared by a casting and solvent evaporation method. The structure, thermal behavior, and mechanical properties of the films were investigated by means of Fourier Transform Infrared Spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and tensile testing. The results indicated that strong hydrogen bonding formed between macromolecules of starch (ST) and konjac glucomannan (KGM), resulting in a good miscibility between ST and KGM in the blends. Compared with the neat ST, the tensile strength of the blend films were enhanced significantly from 7.4 to 68.1 MPa with an increase of KGM content from 0 to 70 wt%. The value of elongation at break of the blend films was higher than that of ST and reached a maximum value of 59.0% when the KGM content was 70 wt% and 20% of glycerol as plasticizer. The incorporation of KGM into the ST matrix also led to an increase of moisture uptake for the ST-based materials. The structure and properties of pea starch-based films were modified and improved by blending with KGM.     

Pectins in the fruits of Japanese quince (Chaenomeles japonica)

The pectin content, composition and physico-chemical properties were studied in the fruits of two genotypes of Japanese quince. On average, the fruits contained 11 g pectins/100 g dry fruit and 1.4 g pectins/100 g fresh fruit. A sequential extraction was used to isolate the pectins from the fruits. The cells from the flesh were examined using a confocal laser scan microscope, fresh and after each extraction step of the sequence. The dilute acid conditions were the most efficient for pectin extraction. Pectins extracted by water or potassium oxalate had higher (>600 ml/g) intrinsic viscosities than the pectins extracted by dilute acid (<400 ml/g). Anionic exchange chromatography was performed on the acid-extracted pectins. They were constituted of four populations, the first one being mainly composed of arabinans, the second one of homogalacturonans, the third one of rhamnogalacturonans. The composition of the last one varied with the genotype studied.     

Biodegradability and mechanical properties of starch films from Andean crops

Different Andean crops were used to obtain starches not previously reported in literature as raw material for the production of biodegradable polymers. The twelve starches obtained were used to prepare biodegradable films by casting. Water and glycerol were used as plasticizers. The mechanical properties of the starch based films were assessed by means of tensile tests. Compost tests and FTIR tests were carried out to assess biodegradability of films. The results show that the mechanical properties (UTS, Young's modulus and elongation at break) of starch based films strongly depend on the starch source used for their production. We found that all the starch films prepared biodegrade following a three stage process and that the weight loss rate of all the starch based films tested was higher than the weight loss rate of the cellulose film used as control.     

Modified natural halloysite/potato starch composite films

Halloysite/potato starch composites were prepared by adding modified natural halloysite nanotubes into potato starch matrices to reenforce the mechanical properties of potato starch films. The halloysite/potato starch films were characterized by X-ray diffraction, scanning electron microscope and infrared spectrometry. Meanwhile, the mechanical properties and transparency of the films were studied. The results show that the modified halloysite nanotubes can be well distributed in the starch matrix and thus the tensile strength of the films was clearly enhanced. The flexibility of the films could be improved through adding glycerol although at the cost of reducing tensile strength. But incorporation of PVA could further improve the tensile strength of the halloysite/potato starch films.     

Preparation and characteristics of oxidized potato starch films

Starch films were developed from oxidized potato starch (OPS) with glycerol as a plasticizer at different contents. The OPS films were transparent and flexible. The mechanical properties of these films were measured, and the results indicated that the film with 19.4% glycerol exhibited the desirable mechanical properties. X-ray diffraction study showed that the increase of glycerol content led to a decrease in the crystallinity for OPS films, and storage conditions such as storage time, storage temperature and relative humidity also had certain effects on the retrogradation of starch owing to re-crystallization. Anti-leakage, anti-crosslinking, and stability in acid or alkali solutions of the OPS films were also studied, and the results indicated that the OPS films had excellent anti-leakage ability for vegetable oil, good anti-crosslinking ability in saturated formaldehyde vapor, and good stability in acid aqueous medium, but poor stability in alkali aqueous medium.     

Influence of thickness on the mechanical properties for starch films

The aim of the present study was to investigate some mechanical properties of starch films. Starch is a natural common polymer in nature and the use of natural materials is increasing in the industries. In this study, the mechanical properties of starch plasticized with 30 parts by weight, of glycerol, are investigated. For the mechanical testing films of different thickness were used, the thickness varied between 0.5 and 2.5 mm. T_g was measured with a differential scanning calorimeter and with a dynamical mechanical analysis. The starch films were tested in tension and characterised in terms of stiffness, strength and failure strain. Fracture toughness was measured by single edge notch tests. Both stiffness and strength showed a strong dependence on film thickness, stronger then expected from linear fracture mechanics. This can be due to the different molecule orientation in the films, and due to the crystallinity of the films.