Bioabsorbable soy protein plastic composites: Effect of polyphosphate fillers on water absorption and mechanical properties

The use of synthetic and natural bioabsorbable plastics has been severely limited due to their low stiffness and strength properties as well as their strong tendency to absorb moisture. This research focused on the development of bioabsorbable polyphosphate filler/soy protein plastic composites with enhanced stiffness, strength, and water resistance. Bioabsorbable polyphosphate fillers, biodegradable soy protein isolate, plasticizer, and adhesion promoter were homogenized and compression-molded. Physical, mechanical, and water absorption testing was performed on the molded specimens. Results showed improvements in stiffness, strength, and water resistance with increasing polyphosphate filler content up to 20% by weight. Application of a coupling agent produced further mechanical property enhancements and a dramatic improvement in water resistance, interpreted by an interfacial chemical bonding model. Examination of the fracture surfaces of the materials revealed that the addition of the polyphosphate fillers changed the failure mode from brittle to pseudo-ductile. These results suggest that these materials are suitable for many load-bearing applications in both humid and dry environments where current soy protein plastics are not usable.     

Influence of Filler Particle Size on Physical Properties and Biodegradation of Biocomposites Based on Low-Density Polyethylene and Lignocellulosic Fillers

This study examined biocomposites based on low-density polyethylene (LDPE) and lignocellulosic fillers [wood flour (WF) and oil flax straw (FS)] selecting four size fractions of each lignocellulosic material as fillers for the composites. The primary aim was to evaluate the influence of fraction size on the composites’ basic properties; to accomplish this, the composites’ mechanical properties, thermal oxidation, thermophysical characteristics, and water absorption capacity were examined. Then microphotographs of the samples were created and length-to-diameter (L/D) ratio of the fillers was calculated, finding that the L/D ratio increased with increasing particle size. The particle size influenced the oxidative degradation and water absorption processes in composites with oil flax but not in those with WF. Biodegradation tests performed on the recovered soil found that the loss of mass in composites based on LDPE and FS was higher than in the same composites with WF. Moreover, at the initial stage of composting, the biodegradation rate correlated with the size of filler particles (i.e., the larger the particles, the higher the degradation rate of the biocomposite).     

Soil Biodegradation of PHBV/Peach Palm Particles Biocomposites

There is great interest in developing eco-friendly green biocomposites from plant-derived natural fibers and crop-derived bioplastics attributable to their renewable resource-based origin and biodegradable nature. Fully biodegradable composites, made from both biodegradable polymeric matrices and natural fibers, should be advantageous in some applications, such as one way packaging. Polyhydroxyalkanoates (PHAs) are naturally occurring biodegradable polymers produced from a wide range of microorganisms, with poly(3-hydroxybutyrate) P(3HB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) being important examples of PHAs. In this work, biocomposites of PHBV consisting of a PHBV matrix incorporating peach palm particles (PPp), [i.e., 100/0, 90/10, 80/20 and 75/25 (%w/w) PHBV/PPp] were processed by injection molding at 160 °C. The effect of PPp loading on the thermal and the mechanical properties, as well as on the morphological behavior of the PHBV/PPp biocomposites was investigated. Soil biodegradation tests were carried out by burying specimen beakers containing aged soil and kept under controlled temperature and humidity in accordance with ASTM G160-98. Degradation of the biocomposites was evaluated by visual analysis, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) following test exposures of up to 5 months. The addition of PPp reduced the maximum strength and the elongation at break of the biocomposites. On the other hand, the Young’s modulus improved with the PPp content. Micrographs of the fracture surfaces following tensile strength testing revealed a large distance between the PHBV matrix and PPp particles although a low interaction is expected. Where measured, these distances tended increase as the PPp content of the biocomposites increased. Soil biodegradation tests indicated that the biocomposites degraded faster than the neat polymer due to the presence of cavities that resulted from introduction of the PPp and that degradation increased with increasing PPp content. These voids allowed for enhanced water adsorption and greater internal access to the soil-borne degrader microorganisms.     

Characterization of poly(lactic acid) biocomposites filled with chestnut shell waste

The aim of this study was to determine thermal and mechanical properties and applicability of ground chestnut shell waste as a filler for poly(lactic acid) composites. The used amount of filler was ranging from 2.5 to 30 wt%. Spectroscopic analysis of composites and its ingredients was conducted by means of FT-IR method. The mechanical and thermal properties of the composites were determined in the course of static tensile test, Dynstat impact strength test, DMTA analysis, and DSC method. The fractured surface morphology of biocomposites was evaluated by SEM analysis. Incorporation of the filler influenced the overall mechanical properties of the composites characterized by high stiffness and lowered impact resistance. Fabricated composites with different amounts of non-reactive natural waste filler exhibited acceptable mechanical and thermal properties. Therefore, these composites can be used as eco-friendly, biodegradable materials for low-demanding applications.     

Pressure- volume- temperature relationships of soy protein isolate/starch plastic

The use of pressure-volume-temperature (PVT) studies in processing of a biodegradable plastic composition made from soy protein isolate and corn starch is described. The ability of PVT measurements to predict the combined effects of pressure, volume, and temperature effects is demonstrated. The results show that the PVT relations of the plastic can be predicted by using a regression analysis similar to the Tait equations of state. A change in slope of the PVT curves was observed at around 80‡C, which is ascribed to the glass-transition process of the plastic. Evidence of onset of thermal degradation of the plastic was observed at ca. 160‡C under 0 to 200 MPa isobaric pressure. This thermal degradation precluded determination of the crystal melting point of the plastic.     

Water-Blown Castor Oil-Based Polyurethane Foams with Soy Protein as a Reactive Reinforcing Filler

To decrease the usage of petroleum based materials, a kind of bio-resource based composite foams were developed with soy protein isolate (SPI) as reactive reinforcing filler in castor oil based polyurethane foams (PUF) prepared by self-rising method using water as a blowing agent. The resulting composite foams were evaluated for their morphology, density, mechanical and biodegradation properties, etc. Fourier transform infrared spectroscopy study exhibited characteristic peaks for SPI and PUF and indicated that the amino groups and hydroxyl groups on SPI reacted with polyphenyl polymethylene polyisocyanates (PAPI) to increase the crosslinking degrees of the composite foams. Densities of the resultant composites were found to increase with increasing SPI content. Mechanical properties of the samples were improved with the increase of SPI content. The compost tests further proved that the composite PUF had better biodegradability than neat PUF. Therefore, this research has provided a simple method of preparing the bio-resource based polyurethane foams, while exploring the potential of using SPI in polyurethane foam applications.     

Modification of Soy Protein Plastic with Functional Monomer with Reactive Extrusion

Chemical modification of soy protein with monomers such as maleic anhydride, glycidyl methacrylate and styrene was accomplished using reactive extrusion technology. Thermal and mechanical properties of the modified soy protein plastics were characterized with differential scanning calorimetry (DSC), a dynamic mechanical analyzer (DMA) and a United Testing System load frame. It was found that the denaturation temperature and the glass transition temperature of soy protein plastic changed. In addition, the tensile properties of modified soy protein plastic improved. Attenuated total reflection Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure of modified soy proteins. A suggestion of the interaction between soy protein and functional group in functional polymers is given. Through the in-situ interaction between the polymer and soy protein plastic, the mechanical properties of the soy protein plastic can be adjusted and controlled.     

Biodegradation of Agricultural Plastic Films: A Critical Review

The growing use of plastics in agriculture has enabled farmers to increase their crop production. One major drawback of most polymers used in agriculture is the problem with their disposal, following their useful life-time. Non-degradable polymers, being resistive to degradation (depending on the polymer, additives, conditions etc) tend to accumulate as plastic waste, creating a serious problem of plastic waste management. In cases such plastic waste ends-up in landfills or it is buried in soil, questions are raised about their possible effects on the environment, whether they biodegrade at all, and if they do, what is the rate of (bio?)degradation and what effect the products of (bio?)degradation have on the environment, including the effects of the additives used. Possible degradation of agricultural plastic waste should not result in contamination of the soil and pollution of the environment (including aesthetic pollution or problems with the agricultural products safety). Ideally, a degradable polymer should be fully biodegradable leaving no harmful substances in the environment. Most experts and acceptable standards define a fully biodegradable polymer as a polymer that is completely converted by microorganisms to carbon dioxide, water, mineral and biomass, with no negative environmental impact or ecotoxicity. However, part of the ongoing debate concerns the question of what is an acceptable period of time for the biodegradation to occur and how this is measured. Many polymers that are claimed to be ‘biodegradable’ are in fact ‘bioerodable’, ‘hydrobiodegradable’, ‘photodegradable’, controlled degradable or just partially biodegradable. This review paper attempts to delineate the definition of degradability of polymers used in agriculture. Emphasis is placed on the controversial issues regarding biodegradability of some of these polymers.     

Processability and Biodegradability Evaluation of Composites from Poly(butylene succinate) (PBS) Bioplastic and Biofuel Co-products from Ontario

This study investigates the processability and biodegradability of composite bioplastic materials. Biocomposites were processed using twin-screw compounding of the bioplastic poly(butylene succinate) (PBS) with bio-based fillers derived from co-products of biofuel production. An extensive biodegradability evaluation was conducted on each biocomposite material, as well as the base materials, using respirometric testing to analyze the conversion of organic carbon into carbon dioxide. This evaluation revealed that the presence of meal-based fillers in the biocomposites increased the rate of biodegradation of the matrix polymer, degrading at a faster pace than both the pure PBS polymer and the switchgrass (SG) composite. This degradation was further confirmed using FT-IR and thermal analysis of the material structure before and after biodegradation. The increased biodegradation rate is attributed to the high concentration of proteins in the meal-based composites, which enhanced the hydrolytic biodegradation of the material and facilitated micro-organism growth. The SG-based composite degraded slower than the pure polymer due to its lignin content, which degrades via a different mechanism than the polymer, and slowed the biodegradation process.     

Processing and Characterization of Glycerol-Plasticized Soy Protein Plastics Reinforced with Citric Acid-Modified Starch Nanoparticles

Citric acid-modified starch nanoparticles with an average size of 82 nm were prepared through precipitation from gelatinized starch solution by ethanol and further modification with citric acid. When being incorporated in glycerol-plasticized soy protein plastics, citric acid-modified starch nanoparticles displayed dramatic reinforcing effect. The resulted nanocomposite plastics exhibited improvement in mechanical performance. Also, the water uptake decreased, indicating an increase of water resistance. The modified starch nanoparticles had a good compatibility with soy protein matrix. Possessing a relative hydrophobic surface, the filler would prefer to interact with protein-rich domains in glycerol-plasticized soy protein. The work provided a green approach of biodegradable materials based on naturally occurring biopolymers.     

Viscosity of Soy Protein Plastics Determined by Screw-Driven Capillary Rheometry

Soy protein plastics are a renewable, biodegradable alternative to fossil fuel-based plastic resins. Processing of soy protein plastics using conventional methods (injection molding, extrusion) has met with some success. Viscosities of processable formulations that contain soy protein along with the necessary additives, such as glycerol and cornstarch, have not been reported, but are necessary for extrusion modeling and the design of extrusion dies. Resins consisting of soy protein isolate-cornstarch ratios of 4:1, 3:2, and 2:3 were plasticized with glycerol and soy oil, compounded in a twin screw extruder and adjusted to 10% moisture. The effects on viscosity of added sodium sulfite, a titanate coupling agent and recycling were evaluated using a screw-driven capillary rheometer at shear rates of 100–800/s. The viscosities fit a power-law model and were found to be shear thinning with power-law indices, n, of 0.18–0.46 and consistency indices, m, of 1.1 × 10⁴–1.0 × 10⁵. Power-law indices decreased and consistency indices increased with increasing soy protein-to-cornstarch ratio and in the absence of sodium sulfite. Addition of the titanate coupling agent resulted in increased power-law index and decreased consistency index. Viscosities at a shear rate of 400/s decreased with recycling, except for the 4:1 soy protein isolate to cornstarch formulation, which displayed evidence of wall slip. Power-law indices were unaffected by recycling. Viscosities in the tested shear rate range were comparable to polystyrene and low-density polyethylene indicating soy protein plastics are potential drop-in replacements for commodity resins on conventional plastics processing equipment.     

Cradle-to-Grave Life Cycle Assessment and Techno-Economic Analysis of Polylactic Acid Composites with Traditional and Bio-Based Fillers

This research focused on life cycle assessment (LCA) and techno-economic analysis (TEA) comparisons of polylactic acid (PLA) composites, in order to compare organic to inorganic fillers. Organic fillers included DDGS, flax, hemp, rice husks, and wood, and were compared against inorganic fillers (glass and talc) for PLA-based composites. This study utilized LCAI and TEA methodology to estimate and quantify costs, emissions, and energy intensity (EI) associated with material acquisition, processing, transport, and end-of-life treatment used during plastic composite production. Emission categories analyzed include global warming potential (GWP), air acidification (AA), air eutrophication (AE), water eutrophication (WE), ozone layer depletion (OLD), air smog (AS), high carcinogens (HC), and high non-carcinogens (HNC). To achieve a “Cradle-to-Grave” perspective, two models were meshed, the plastic comparator (PC) and EIO-LCA (EIO), to simulate the EI and emissions associated over the entire life cycle. Based assumptions used, this research has shown that utilizing land fill end-of-life treatment and glass filler composite was the most environmentally harmful option, and maintained the highest economic impact, for all impact categories during PLA composite production. Alternatively, both DDGS and wood filler composites paired with recycling end-of-life treatment were shown to be the least environmentally damaging method and incurred the lowest cost of all PLA composites considered. This study also suggests that utilization of organic bio-based fillers produces a lower economic/environmental impact, and EI, compared to utilization of inorganic fillers in PLA composites. Accordingly, this research has demonstrated the impact of LCA/TEA paired analysis when assessing the bioplastic and biocomposite processing, which may be utilized as a precursor for parallel research undertakings.     

Preliminary Studies on Converting Agricultural Waste into Biodegradable Plastics – Part III: Sawdust

Summary Hardwood sawdust was derivatized either by carboxymethylation, glutaration, maleiation, phthallation, or succination in order to produce anionic materials suitable for complexation with soy protein isolate. Blending each derivative with soy protein isolate resulted in instant precipitation of gels. Infrared spectroscopy and differential scanning calorimetry suggested that each derivative formed a complex with protein. Reaction products could be dried into pellets exhibiting tensile strengths between 0.9–2.4 MPa, suggested that these materials could be promising candidates for biodegradable structural materials.     

Man-Made and Natural Fibres as a Reinforcement in Fully Biodegradable Polymer Composites: A Concise Study

Biodegradable and ecologically friendly polymer materials attract great attention of many scientific groups in the world as they fit well in the sustainable development policy and are considered to be “a right thing to do” by the general public. Such polymers can be modified by the addition of different fillers, favorably of natural origin. In the paper we provide a comparison between composites based on two biodegradable polymers: poly(lactic acid)—biodegradable, natural stock polymer and poly(butylene succinate)—biodegradable polymer produced from fossil based materials. For each polymer we have prepared a series of composites with different fibres (natural: hemp and flax, and manmade: Cordenka) and different filler loadings. To fully characterize obtained materials thermal, mechanical and surface free energy measurements were performed, completed with morphology observations and an attempt to compare the experimental data for tensile measurements with values obtained using the modified rule of mixtures. The tensile results calculated using the modified rule of mixture for below 30% fibre loading are found to be fitting the experimental data. Composites mechanical properties and morphology were strongly affected by the type of fibre used and its loading, however thermal properties remained almost unchanged. In specific, Cordenka fibres tend to form bunches which presence greatly influences the mechanical properties but still our studies have shown clear advantage of manmade Cordenka fibres over the hemp and flax fibres when considering distribution and fibre–polymer interaction.     

Dialdehyde starch and zein plastic: Mechanical properties and biodegradability

Dialdehyde starch (DAS) and zein, a hydrophobic corn protein, were investigated to produce biodegradable plastics with improved water resistance and mechanical properties. In the study, dialdehyde starch and zein ratio, plasticizers, and degree of starch oxidation were examined. Increased molding temperature and level of starch oxidation decreased water absorption of the plastic. Tensile strength and Young's modulus increased with starch oxidation. The biodegradation of starting materials and ground plastic specimens was studied in aerobic soil reactors maintained at 25°C for 180 days. Biodegradation of corn starch, zein, and dialdehyde starch for 180 days produced CO₂ equivalent to 64, 63, and 10% of theoretical carbon, respectively. Specimens of molded DAS and zein (3 : 1) plastic showed accelerated CO₂ evolution compared to DAS and other raw materials alone. By 180 days, specimens made with starch of low oxidation (1 and 5% oxidized) demonstrated a 60% biodegradation, and specimens with highly oxidized starch (90% oxidized) achieved 37% biodegradation.Paper presented at the Bio/Environmentally Degradable Polymer Society—Third National Meeting, June 6–8, 1994, Boston, Massachusetts.Journal Paper J-15927 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Project No. 3258.     

Preliminary Studies on Converting Agricultural Waste into Biodegradable Plastics,Part I: Corn Distillers’ Dry Grain

Distillers dry grain (DDG) was derivatized either by carboxymethylation, glutaration, maleiation, phthallation, or succination in order to produce anionic materials suitable for complexation with soy protein isolate. Infrared spectroscopy confirmed that derivatization of DDG by all reagents was successful. Blending of derivatized anionic products with soy protein resulted in instant precipitation of gels. The gels were centrifuged, molded, and dried into solid pellets with tensile strengths as high as 1.67MPa, suggesting that these materials could be promising as biodegradable structural materials. Infrared spectroscopy suggested the possibility of complexes forming between soy protein isolate and each of the derivatized DDG samples.     

Preliminary Studies on Converting Agricultural Waste into Biodegradable Plastics—Part IV: Polysaccharide Containing Natural Materials

Corn distillers’ dry grain, corncob powder, hardwood powder, and sugar beet pulp were separately anionized by oxidation with sodium hypochlorite in aqueous solution. Solid reaction products instantly precipitated upon admixing each of the above-oxidized materials with soy protein isolate. Infrared spectra and differential scanning calorimetry supported the hypothesis that soy protein isolate complexed with all of the above-oxidized polysaccharides. Reaction products with either oxidized corn distillers’ dry grain or oxidized sugar beet pulp provided hard, brittle pellets with tensile strengths as high as 9.5 MPa, suggesting that these materials could be viable as biodegradable plastics.     

A Method for Measuring Degradation of Individual Components in Multicomponent Biodegradable Plastics by Fourier Transform Infrared Spectrometry

A new chemometric method based on Beer's law was derived that uses peak ratios from Fourier transform infrared spectra of neat polymers and their composite plastics to quantify degradation of the individual polymers after biodegradation. The method affords direct measurement of polymer concentrations and weight losses without prior calibration against known composites. Unlike traditional chemometric methods, this method does not require sampling of as many or more different composites as the number of polymers in the composite being analyzed. When the neat polymer spectra are known, only two measurements, one before and one after biodegradation, are needed. A potentially major advance is that the method allows automation of analytical infrared wavelength selection by computer from all possible wavelength combinations. In this paper, the theoretical basis and derivation of the mathematical model for multicomponent systems is presented. The validity of the model was proved initially by applying the method to simulated two-polymer and three-polymer composites and finally by comparing test results with known samples of biodegradable composites prepared in the laboratory. Potential future development of the method for more challenging multicomponent plastics is discussed.     

Comparative Biodegradation in Soil Behaviour of two Biodegradable Polymers Based on Renewable Resources

This work presents the last phase of long-term experimental studies on the biodegradation in soil behaviour of polymers destined for agricultural applications. The paper focuses on comparative studies between the biodegradation in soil behaviour of two important biodegradable polymers based on renewable resources: poly(lactic acid) (PLA) versus polyhydroxyalkanoates (PHA). Full-scale experiments were carried out during the period June 2008–January 2009. Different methods of exposure were applied in the case of polyhydroxyalkanoates, simulating the agricultural biodegradable mulching films use and their fate in soil after the end of their useful lifetime. The field results were compared with the results of biodegradation under controlled laboratory conditions simulating biodegradation in soil, using soil from the experimental field. Further, the field results were compared against the results of biodegradation under farm composting conditions.     

Thermal and Mechanical Properties of Plastics Molded from Sodium Dodecyl Sulfate-Modified Soy Protein Isolates

Soybean protein is a potential material for manufacturing of biodegradable plastics. The objective of this investigation was to characterize the thermal and mechanical properties of plastics made from sodium dodecyl sulfate (SDS)-modified soy proteins. Soy protein isolate (SPI) was prepared from defatted soy flour, modified with various concentrations of SDS, and then molded into plastics. The temperatures of denaturation of the modified soy protein increased at low SDS concentration and then decreased at high SDS concentration. At the same SDS concentration, the plastics molded from the modified soy proteins showed a similar temperature of denaturation, but a lower enthalpy of denaturation compared to the modified soy protein. Young's modulus of the plastics decreased as SDS concentration increased, and the tensile strength and strain at break of the plastics reached a maximum value at 1% SDS modification. Two glass transition temperatures were identified corresponding to the 7S and 11S globulins in SPI by dynamic mechanical analysis, and they decreased as SDS concentration increased. The SDS modification increased the water absorption of the plastics.