Role of Hydrophilic and Hydrophobic Interactions in Structure Development of Zein Films

Zein has been studied for its potential as a biobased polymeric material. Due to the fact that films made exclusively from zein are brittle, composites of zein and oleic acid were prepared in our lab and formed into flexible films. Film properties were believed related to their structure. X-ray scattering measurements on zein films suggested the formation of layers along the plane of the film. Oleic acid seemed to play an important role in layer formation. However, X-ray measurements could not yield information on the nature of the interface between oleic acid and zein. Surface plasmon resonance (SPR) was used to further investigate interaction between zein and oleic acid. Dynamic adsorption of zein from alcoholic solutions onto hydrophilic and hydrophobic surfaces generated by self-assembled monolayers of 11-mercaptoundecanoic acid or 1-octanethiol was monitored by SPR. It was observed that zein had a greater affinity for hydrophilic than for hydrophobic surfaces under the prevalent experimental conditions. A mechanism for structure development of zein-oleate films was proposed based on these results and previous X-ray measurements. It is suggested that the structure development involves hydrophilic adsorption of fatty acids onto the zein surface followed by hydrophobic associations leading to a layered film structure organization.     

Influence for Soil Environment by Continuing use of Biodegradable Plastic

The influence on soil environment by continuing use of the biodegradable plastic films (biodegradable mulching films) in farmland was investigated. The difference was not seen in the amount of soil bacteria between mulching film plowing sections and non-plowing sections. The total bacteria amount did not increase by the effect of plowing the biodegradable mulching film. Poly-(butylene succinate and adipate) (PBSA) and poly-(ε-caprolactone) (PCL) decomposing bacteria did not increase in PBSA and PCL mulching film plowing sections comparing polyethylene covering section (PE) and no-film section. Polylactic acid (PLA) decomposing bacteria were not detected in all sections. Total denaturing gradient gel electrophoresis (DGGE) band patterns did not show a clear transition of the bacterial community structure in both the cultivating and promoting sections. In usual usage condition of the biodegradable plastic films, it was hardly influence to the soil environment such as bacterial community structure in farmland.     

Feasibility study of the separation of chlorinated films from plastic packaging wastes

This study describes the possible separation of chlorinated plastic films (PVC and PVDC) from other heavy plastic packaging waste (PPW) by selective twist formation and gravity separation. Twists formation was mechanically induced in chlorinated plastic films, whereas twist formation did not occur in PS and PET films. After twist formation, all the films had the apparent density of less than 1.0 g/cm³ and floated in water even though the true density was more than 1.0 g/cm³. However, the apparent density of the PS and the PET films increased with agitation to more than 1.0 g/cm³, whereas that of chlorinated plastic films was kept less than 1.0 g/cm³. The main reason would be the air being held inside the chlorinated plastic films which was difficult to be removed by agitation. Simple gravity separation after twist formation was applied for artificial film with 10 wt.% of the chlorinated films and real PPW films with 9 wt.% of the chlorinated films. About 76 wt.% of the artificial PPW films and 75 wt.% of real PPW films after the removal of PP and PE were recovered as settling fraction with 4.7 wt.% and 3.0 wt.% of chlorinated plastic films, respectively. These results indicate that simple gravity separation process after twist formation can be used to reduce the chlorinated plastic concentration from mixed heavy PPW films.     

Oxygen Permeability and Biodegradability of Polyuronic Acids Prepared from Polysaccharides by TEMPO-Mediated Oxidation

Polyuronic acids, i.e., amylouronic acid, cellouronic acid and chitouronic acid, were prepared from starch, cellulose and chitin, respectively, by the 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO)-mediated oxidation, and their gas-barrier properties and biodegradability were studied in consideration to use the polyuronic acids as flexible packaging films or coating materials. Cellouronic acid and amylouronic acid had excellent oxygen-barrier properties similar to that of poly(vinyl alcohol) (PVA), while chitouronic acid did not. The regular chemical structures of the former two polyuronic acids with no bulky substituents or adducts may have brought about such high oxygen-barrier levels. An oxidized product prepared form fine microcrystalline cellulose by the TEMPO-mediated oxidation was not completely dissolved in water, but became a paste. However, this paste also formed sufficiently smooth films by coating, and had good gas-barrier property. All polyuronic acids prepared were biodegradable; cellouronic acid and chitouronic acid had high degrees of biodegradability, while amylouronic acid had quite low value. These various characteristics are significant for end use of these new polyuronic acids as gas-barrier materials for biodegradable packaging.     

Production of Poly(3-hydroxyalkanoate)s by Pseudomonas putida Cultivated in a Glycerol/Nonanoic Acid-Containing Medium

The biosynthesis of poly(3-hydroxyalkanoate) (PHA) by Pseudomonas putida (JCM6160) cultivated in a medium containing glycerol, nonanoic acid, or a glycerol/nonanoic acid mixture as the sole carbon sources was investigated. The PHA content was ~20 % when glycerol was the carbon source. This relatively low content can be attributed to the glycerol end-cap effect and the absence of enzymes that can directly synthesize PHA from acetyl CoA, which is the major metabolite of glycerol. Fatty acids, containing even numbered carbons, are synthesized from acetyl CoA, and they can be used as substrates for PHA synthesis. However, this process also results in decreasing PHA content as fatty acids are siphoned off into other pathways. However, addition of 5 mM nonanoic acid into a 20 mM glycerol-containing medium dramatically increased the PHA content in P. putida, which was 1.3 times larger than the sum of the values found when glycerol and nonanoic acid were each used as the sole carbon source. The PHA, synthesized in the glycerol/nonanoic acid medium, contains 3-hydroxy alkanoate units that have 5, 6, 7, 8, 9, or 10 carbons. The units that contain the even numbered carbons are derived from fatty acids that were produced from glycerol; whereas, the PHA units with the odd numbered carbons are derived from nonanoic acid. Pentanoate units were also found in the polyester derived from glycerol and nonanoic acid, and must have been synthesized indirectly via β-oxidation of nonanoic acid with the assistance of glycerol because pentanoate units were not found in PHA when P. putida was cultivated in the presence of only nonanoic acid.     

Biodegradability of Starch Based Self-Supporting Antimicrobial Film and Its Effect on Soil Quality

Alarming environmental pollution from petroleum based non-biodegradable disposable packaging films has generated concern for development of alternatives from natural polymers such as starch. In the present work, the biodegradability of a self-supporting film made from starch and polyvinyl alcohol (PVA) (starch:PVA?=?9:1 as the polymer) together with glutaraldehyde as crosslinker and sodium propionate (SP) as antimicrobial was investigated by soil burial method. The changes in soil composition namely pH, organic carbon, available and total nitrogen, and water holding capacity as a result of biodegradation were also estimated. The film underwent ≈?90% biodegradation within a period of 28 days, with simultaneous increase in soil nutrients. Moreover, the pH remained in the accepted limit for plant growth. Thus, antimicrobial in the film did not hamper its biodegradation, rather disposal of the film in soil might facilitate plant growth.     

Synthesis of cellulose-fatty acid esters for use as biodegradable plastics

Long-chain fatty acid carbohydrate esters (FACE) were synthesized by the acid chloride-pyridine reaction to different degrees of substitution (DS). The hydrolyzed soybean oil was used as the source of unsaturated fatty acids. High molecular weight FACE polymers are insoluble in common solvents, such as benzene, toluene, THF, etc., and are highly water resistant. However, FACE polymers of hydrolyzed cellulose (MW 180 kD) are soluble/swellable in toluene and can be cast into tough, flexible films. FACE polymer properties of tensile strength and clasticity vary with degree of substitution and polymer size.Paper presented at the Bio/Environmentally Degradable Polymer Society—Third National Meeting, June 6–8, 1994, Boston, Massachusetts.     

Organic–Inorganic Hybrid Coatings for the Modification of Barrier Properties of Poly(lactic acid) Films for Food Packaging Applications

Organic–inorganic hybrid coatings based on poly(ε-caprolactone), poly(ethylene oxide) or poly(lactic acid) as organic phase and silica from tetraethoxysilane as inorganic phase were prepared by the sol–gel approach. Coatings were applied onto poly(lactic acid) films for food packaging in order to improve its barrier properties towards oxygen and water vapour. All the prepared coatings were dense, homogeneous layers characterized by a good adhesion to the substrate. The permeance of the coating layers resulted one order of magnitude lower than that of the uncoated poly(lactic acid) (PLA) film. The hydrophilic character of the coating did not permit to gain a significant decrease in the water vapour permeance. The perfect visual transparency of the coatings allows their application without worsening of the esthetical properties of the substrate PLA film.     

Comparison of different procedures to stabilize biogas formation after process failure in a thermophilic waste digestion system: influence of aggregate formation on process stability

Following a process failure in a full-scale biogas reactor, different counter measures were undertaken to stabilize the process of biogas formation, including the reduction of the organic loading rate, the addition of sodium hydroxide (NaOH), and the introduction of calcium oxide (CaO). Corresponding to the results of the process recovery in the full-scale digester, laboratory experiments showed that CaO was more capable of stabilizing the process than NaOH. While both additives were able to raise the pH to a neutral milieu (pH>7.0), the formation of aggregates was observed particularly when CaO was used as the additive. Scanning electron microscopy investigations revealed calcium phosphate compounds in the core of the aggregates. Phosphate seemed to be released by phosphorus-accumulating organisms, when volatile fatty acids accumulated. The calcium, which was charged by the CaO addition, formed insoluble salts with long chain fatty acids, and caused the precipitation of calcium phosphate compounds. These aggregates were surrounded by a white layer of carbon rich organic matter, probably consisting of volatile fatty acids. Thus, during the process recovery with CaO, the decrease in the amount of accumulated acids in the liquid phase was likely enabled by (1) the formation of insoluble calcium salts with long chain fatty acids, (2) the adsorption of volatile fatty acids by the precipitates, (3) the acid uptake by phosphorus-accumulating organisms and (4) the degradation of volatile fatty acids in the aggregates. Furthermore, this mechanism enabled a stable process performance after re-activation of biogas production. In contrast, during the counter measure with NaOH aggregate formation was only minor resulting in a rapid process failure subsequent the increase of the organic loading rate.     

The Effect of Polymeric Chain Extenders on Physical Properties of Thermoplastic Starch and Polylactic Acid Blends

The effects of a polymeric chain extender on the properties of bioplastic film made from blends of plasticized polylactic acid (p-PLA) and thermoplastic starch (TPS) were studied. Joncryl^? ADR 4370S, a polymeric chain extender, was blended with TPS and p-PLA at a level of 1% (w/w). A co-rotating twin-screw extrusion process was used to prepare films with various ratios of TPS and p-PLA. Mechanical and physical properties of films, including film tensile properties, surface energy, moisture content, hydrophilicity, moisture sorption behaviour and thermal mechanical properties were determined. During extrusion, films enhanced by 1% Joncryl addition demonstrated more desirable and consistent qualities, such as smoother film edge and surface. Addition of Joncryl significantly improved film tensile strength, 0.2% offset yield strength, and elongation, especially evident with the 250% elongation of 70/30 (TPS/p-PLA) film. Total surface energy of films was not significantly influenced by addition of Joncryl. However, the polar contribution to the total surface energy of 70/30 (TPS/p-PLA) film increased after the addition of Joncryl. The study showed that blending TPS with p-PLA transformed TPS film from being highly hydrophilic to highly hydrophobic. On the other hand, addition of Joncryl had limited effects on moisture content, water solubility, glass transition temperature and moisture sorption behaviour of TPS/p-PLA blend films.     

Mechanical Properties with the Functional Group of Additives for Starch/PVA Blend Film

This paper deals with the mechanical properties and degree of swelling (DS) of starch/PVA blend film with the functional groups i.e., hydroxyl and carboxyl group, of additives. Starch/PVA blend films were prepared by using the mixing process. Glycerol (GL) with 3 hydroxyl group, sorbitol (SO) with 6 hydroxyl group, succinic acid (SA) with 2 carboxyl group, malic acid (MA) with 1 hydroxyl and 2 carboxyl group, tartaric acid (TA) with 2 hydroxyl and 2 carboxyl group and citric acid (CA) with 1 hydroxyl and 3 carboxyl group were used as additives. The results of measured tensile strength (TS) and elongation (%E) verified that both hydroxyl and carboxyl group as a functional groups increased the flexibility and strength of the film. Values of DS for GL-added and SA-added films were low. However, DS values of the films added MA, TA or CA with both hydroxyl and carboxyl group were comparatively high. When the film was dried at low temperature, the properties of the films were evidently improved. The reason is probably because the hydrogen bonding was activated at low temperature.     

Evaluation of Biodegradable Films Made of Waste Mycelium and Poly (Vinyl Alcohol) on the Yield of Pak-Choi

Novel biodegradable films were prepared via blending of poly (vinyl alcohol) and waste mycelium from sauce residue and citric acid fermentation residue, respectively. The performance of these two types of films when used as alternative covers for pak-choi growth under semi-arid climatic conditions was evaluated via field test towards their abilities for water retention and biodegradation, together with the impact on the yield and nutritional quality of pak-choi. Experimental results showed that the use of these films could result in 50% higher water retention than a blank control film after 96-h treatment at 40?°C. Films were biodegraded within 14?weeks under natural conditions, leading to a significant mineralization, progressively releasing over 56% of K⁺, NO₃ ^?, Mg²⁺ and organics, beneficial for plant growth as fertilizer. The yield of pak-choi was increased by 80% in weight when using these films compared with the unmulched control. Compared to those treated with traditional LDPE mulching film, the average contents of chlorophyll, crude protein and soluble sugar in pak-choi were increased by 52.9, 7.2, 80.7% (blends of sauce residue) and 26.7, 11.4, 10.8% (blends of citric acid fermentation residue), respectively.     

Biodegradability of chitin- and chitosan-containing films in soil environment

The biodegradation of polyethylene-chitin (PE-chitin) and polyethylene-chitosan (PE-chitosan) films, containing 10% by weight chitin or chitosan, by pure microbial cultures and in a soil environment was studied. Three soil-inhabited organsims,Serratia marcescens, Pseudomonas aeruginosa, andBeauveria bassiana were able to utilize chitin and chitosan in prepared PE-chitin and PE-chitosan films after eight weeks of incubation at 25°C in a basal medium containing no source of carbon or nitrogen. In a soil environment, the biodegradation of those films was studied and compared with a commercial biodegradable film containing 6% by the weight of corn starch. In soil placed in the lab, 73.4% of the chitosan and 84.7% of the chitin in the films were degraded, while 46.5% of the starch in the commercial film was degraded after six months of incubation. In an open field, 100% of the chitin and 100% of the chitosan in the films were degraded, but only 85% of the starch in the commercial film was degraded after six months of incubation. The weight of controls, (polyethylene films), remained mainly stable during the incubation period. Both PE-chitin and PE-chitosan films degraded at a higher rate than the commercial starch-based film in a soil environment indicating the potential use of chitin-based films for the manufacturing of biodegradable packaging materials.     

Studies on enhanced degradable plastics. III. The effect of weathering of polyethylene and (ethylene-carbon monoxide) copolymers on moisture and carbon dioxide permeability

Two enhanced-photodegradable polyethylenes were studied to determine the effect of photooxidative degradation upon transport properties. Water vapor permeability of LDPE films containing metal compound prooxidants, weathered to different extents under outdoor exposure was studied. A film made of LDPE blended with 20 wt% of polycaprolactone was also examined to determine if biodegradation over a 40-day period resulted in a measurable change in its water vapor transport characteristics. A gravimetric technique was used to study the effects of outdoor and weather-ometer exposures on the permeability of carbon dioxide of both the LDPE film and (ethylene-carbon monoxide) copolymer films. Generally, photooxidative degradation was seen to be accompanied by a change in transport characteristics of the polymer films.     

Life Cycle Analysis of Extruded Films Based on Poly(lactic acid)/Cellulose Nanocrystal/Limonene: A Comparative Study with ATBC Plasticized PLA/OMMT Systems

Life cycle analysis (LCA) of limonene plasticized poly(lactic acid) (PLA) films containing cellulose nanocrystals (CNC) extracted, by acid hydrolysis, from Phormium tenax leaf fibres, was assessed and compared with the results of acetyl tributyl citrate (ATBC) plasticized PLA films, having equivalent mechanical properties, containing organo-modified montmorillonite (OMMT). Eco-Indicator 99 tool has been adopted as the main method for life cycle assessment. Results indicated that, despite CNC are biobased fillers obtained by natural sources, the related chemical extraction leads to a large environmental footprint and a relatively relevant energy expense. LCA characterization of these films demonstrated that the environmental impact of PLA/limonene film reinforced with 1% in weight of CNC (PLA/CNC/limonene) is comparable to the environmental impact of polylactic acid films reinforced with OMMT and plasticized with a petroleum based plasticizer (ATBC) (PLA/OMTT/ATBC). A “cradle to gate” approach has been considered for both the film typologies.     

Properties of Starch/PVA Blend Films Containing Citric Acid as Additive

Starch/polyvinyl alcohol (PVA) blend films were prepared successfully by using starch, polyvinyl alcohol (PVA), glycerol (GL) sorbitol (SO) and citric acid (CA) for the mixing process. The influence of mixing time, additional materials and drying temperature of films on the properties of the films was investigated. With increase in mixing time, the tensile strength (TS), elongation (%E), degree of swelling (DS) and solubility (S) of the film were equilibrated. The equilibrium for TS, %E, DS and S value was 20.12 MPa, 36.98%, 2.4 and 0.19, respectively. The mixing time of equilibrium was 50 min. TS, %E, DS and S of starch/PVA blend film were examined adding glycerol (GL), sorbitol (SO) and citric acid (CA) as additives. At all measurement results, except for DS, the film adding CA was better than GL or SO because hydrogen bonding at the presence of CA with hydroxyl group and carboxyl group increased the inter/intramolecular interaction between starch, PVA and additives. Citric acid improves the properties of starch/PVA blend film compared to glycerol and sobitol. When the film was dried at low temperature, the properties of the films were clearly improved because the hydrogen bonding was activated at low temperature.     

Degradation studies of novel degradable starch-polyethylene plastics containing oxidized polyethylene and prooxidant

Linear low-density polyethylene films were prepared that contained native corn starch (7, 14, or 28%), low or high molecular weight oxidized polyethylene (15%), and a prooxidant mixture (18% POLYCLEAN II) that contains manganese and vegetable oil. For each mixture all components were first mixed at high temperatures in a twin-screw extruder and pelletized. The pellets were cast into films using a single-screw extruder. Oxidized-polyethylene addition did not impair the transparency and thickness of the films and did not reduce the percentage elongation, whereas significant reductions in film mechanical properties were observed. Thermal and photodegradation properties of each film were evaluated by 70°C forced-air oven treatment (20 days), by high-temperature, high-humidity treatment in a steam chamber (20 days), and by exposure to ultraviolet light (365 nm; 4 weeks). Changes in the mechanical properties of the films were determined by an Instron Universal Test Machine; in the carbonyl index, Fourier transform infrared spectroscopy; and in molecular weight, by high-temperature gel-permeation chromatography (HT-GPC). The addition of oxidized polyethylene, especially high molecular weight oxidized polyethylene, and up to 14% starch to the films significantly increased the rate of thermal and photodegradation.Journal Paper No. J-15363 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project No. 0178 and 2889.     

Polyvinyl Alcohol (PVA)/Starch Bioactive Packaging Film Enriched with Antioxidants from Spent Coffee Ground and Citric Acid

The bioactive packaging polyvinyl alcohol (PVA)/starch films were prepared by incorporating combined antioxidant agents i.e. extracted spent coffee ground (ex-SCG) and citric acid. Effect of citric acid content on chemical compatibility, releasing of antioxidant, antibacterial activities, and physical and mechanical properties of PVA/starch incorporated ex-SCG (PSt-E) films was studied. The results of ATR-FTIR spectra showed that antioxidant agents of ex-SCG can penetrate into the film and the ester bond of blended films by citric acid was also observed. The presence of ex-SCG increased efficiency of antioxidant release and antimicrobial activity. The PSt-E film incorporated 30 wt% citric acid showed minimum inhibitory concentration against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The incorporation of ex-SCG and citric acid into film showed a synergistic effect on antibacterial activity. The water resistance and kinetic moisture sorption improved with incorporation of citric acid. The tensile strength and biodegradability of samples were in range of 5.63–7.44 MPa and 65.28–86.64%, respectively. Based on this study, PSt-E film incorporated 30 wt% citric acid can be applied as novel food packaging materials.     

Characterization of Biodegradable Polymer Blends of Acetylated and Hydroxypropylated Sago Starch and Natural Rubber

Development of biodegradable polymers from absolute environmental friendly materials has attracted increasing research interest due to public awareness of waste disposal problems caused by low degradable conventional plastics. In this study, the potential of incorporating natural rubber latex (NRL) into chemically modified sago starch for the making biodegradable polymer blends was assessed. Native sago starch was acetylated and hydroxypropylated before gelatinization in preparing starch thermoplastic using glycerol. They were than casted with NRL into biopolymer films according to the ratios of 100.00/0.00, 99.75/1.25, 98.50/2.50, 95.00/5.00, 90.00/10.00 and 80.00/20.00 wt/wt, via solution spreading technique. Water absorption, thermal, mechanical, morphological and biodegradable properties of the product films were evaluated by differential scanning calorimetry (DSC), universal testing machine (UTM), scanning electron microscopy (SEM) and fourier transform infrared spectroscopy. Results showed that acetylation promoted the incorporating behavior of NRL in sago starch by demonstrating a good adhesion characteristic and giving a uniform, homogenous micro-structured surface under SEM observation. However, the thin biopolymer films did not exhibit any remarkable trend in their DSC thermal profile and UTM mechanical properties. The occurrence of NRL suppressed water adsorption capacity and delayed the biodegradability of the biopolymer films in the natural environment. Despite the depletion in water adsorption capacity, all of the product films degraded 50 % within 12 weeks. This study concluded that biopolymers with desirable properties could be formulated by choosing an appropriate casting ratio of the sago starch to NRL with suitable chemical substitution modes.     

Properties of Wheat-Gluten/Montmorillonite Nanocomposite Films Obtained by a Solvent-Free Extrusion Process

This is, to our knowledge, the first study of wheat-gluten-based nanocomposite films prepared by a solvent-free extrusion process. Wheat gluten/montmorillonite nanocomposite films were obtained in a single screw-extruder using urea as a combined denaturant and plasticizer. The oxygen permeability and water vapor transmission rate of the films decreased by respectively factors of 1.9 and 1.3 when 5 wt.% clay was added. At the same time, the stiffness increased by a factor of 1.5, without any critical loss of extensibility. Field emission scanning electron microscopy (FE-SEM) and Energy-dispersive X-ray analysis indicated that the clay particles were layered mainly in the plane of the extruded film. It was possible to identify individual platelets/tactoids with FE-SEM and, together with findings from transmission electron microscopy, atomic force microscopy and X-ray diffraction, it was concluded that the clay existed as individual clay platelets, intercalated tactoids and agglomerates. Thermogravimetric analysis showed that the thermal stability of the extrudates was improved by the addition of clay.