Mechanical properties and biodegradability of crosslinked soy protein isolate/waterborne polyurethane composites

With anionic waterborne polyurethane (WPU) as a plasticizer and ethylene glycol diglycidyl ether (EGDE) as a crosslinker, we successfully prepared crosslinked soy protein isolate (SPI) plastics. Anionic WPU was mixed with SPI and EGDE in an aqueous dispersion at room temperature. The mixed aqueous dispersion was cast and cured, and the obtained material was pickled and hot‐pressed to produce the crosslinked SPI/WPU sheets. The resulting sheets containing about 60 wt % SPI were characterized with infrared spectroscopy, scanning electron microscopy, atomic force microscopy, dynamic mechanical analysis, and tensile testing, and biodegradation testing of the sheets was performed in a mineral salt medium containing microorganisms. The results revealed that the crosslinked SPI/WPU plastics with EGDE concentrations of 2–4 wt % possessed high miscibility, good mechanical properties, and water resistivity. In addition, the crosslinked sheets could be biodegraded, and the half‐life of the biodegradation for a sheet crosslinked with 3 wt % EGDE was calculated to be less than 1 month. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 465–473, 2005     

Ways of strengthening biodegradable soy‐dreg plastics

Biodegradable plastics (GSD) based on soy dreg (SD) were prepared by compression‐molding, with glycerol as the plasticizer and glutaraldehyde (GA) as the cross‐linker. The structure and properties of the GSD sheets were investigated by Fourier‐transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), scanning electron microscope (SEM), and tensile test methods. The results indicate that when GA content was 6.8%, the tensile strength (σ_b) of the sheet reached the maximum value of 14.5 MPa. Moreover, the strength and water resistance of the sheets coated with castor‐oil‐based polyurethane/nitrochitosan interpenetrating network (IPN) coating were significantly enhanced to 24.6 MPa in the dry state and 9.8 MPa in the wet state. Simultaneously, the test of biodegradability of the GSD sheet in a mineral salts medium containing microorganisms and agar proved that GSD could be fully biodegradable. This work has provided a novel way to utilize low‐cost SD to prepare biodegradable plastics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 422–427, 2003     

Structure and mechanical properties of soy protein materials plasticized by Thiodiglycol

Thiodiglycol (TDG) is a relatively nontoxic compound from organic wastes. By using TDG as a plasticizer with weights from 2.5 to 40%, we prepared soy protein isolate (SPI) films by a compression‐molding technique at 140°C and 15 MPa. The TDG‐plasticized films (SPI–TDG films) were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, dynamic mechanical thermal analysis, thermogravimetric analysis, optical transmittance, and water uptake experiments. The SPI–TDG film plasticized with 25% TDG exhibited good mechanical properties, such as a tensile strength and modulus of 20.3 and 582 MPa, respectively, whereas the SPI–glycerol film with 25% glycerol had a tensile strength and modulus of 16.2 and 436 MPa, respectively. The results from the thermogravimetric analysis and water uptake experiments indicated that the thermal stability and water resistance of the TDG‐plasticized SPI materials were higher than that of the glycerol‐plasticized one. The improvements in the mechanical properties, water resistance, and thermal stability of the SPI–TDG films could be attributed to the strong intermolecular hydrogen bonding between soy protein and TDG and the presence of fewer hydroxyl groups in TDG, as compared structurally with glycerol. This study provided a new plasticizer for the preparation of soy protein materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of lignin as a filler on properties of soy protein plastics. I. Lignosulfonate

A series of biodegradable plastics from soy protein isolate (SPI) and lignosulfonate (LS) with a weight ratio of 0:10 to 6:4 were prepared with 40 wt % glycerol as a plasticizer by compression molding. Their properties were investigated by wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamical mechanical thermal analysis (DMTA), scanning electron microscopy (SEM), and tensile tests. The results indicated that the introduction of a moderate LS content from 30 to 40 parts in the blends could simultaneously enhance the tensile strength, elongation, and Young's modulus of soy protein plastics alone. Studies of the water sensitivity of the materials suggested that the strong interaction between LS and SPI could restrict the effect of water on the swelling and the damage of the materials, resulting in lower water absorption. The improvement of the properties was attributed mainly to the existence of the beneficial microphase separation and the formation of crosslinked structures because of the introduction of LS into soy protein plastics. Therefore, a model of a crosslinked network formed from SPI molecules with an LS center was established based on the existence of strong physical interactions between LS and SPI. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3284–3290, 2003     

Properties of molded soy protein isolate plastics

Thermal property of soy protein isolates (SPI) was studied with differential scanning calorimetry and thermogravimetric analysis. The weight loss of pure SPI is about 300°C. The glass transition temperature (T_g) is above 200°C. The best molding temperature of glycerin plasticized SPI plastics were then given. It is between 125 and 140°C. Subsequently the special property of molded SPI plastics was investigated. Results show that the atmosphere humidity affects the mechanical property and thermal property of SPI plastics. With the increasing humidity, the tensile strength decreases. While the elongation at breakage and peak area of the differential scanning calorimetry curve increases. At high temperature even at 140°C the molding temperature SPI plastics still have tensile strength though it decreases with the increasing test temperature while elongation at breakage increases. Dynamic mechanic thermal analysis test show that the storage modulus decreases with the rising temperature. The mechanical loss peak appears at lower temperature with the increasing amount of glycerin content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Properties of soy protein isolate/poly(vinyl alcohol) blend “green” films: Compatibility,mechanical properties,and thermal stability

Blend films from nature soy protein isolates (SPI) and synthetical poly(vinyl alcohol) (PVA) compatibilized by glycerol were successfully fabricated by a solution‐casting method in this study. Properties of compatibility, mechanical properties, and thermal stability of SPI/PVA films were investigated based on the effect of the PVA concentration. XRD tests confirm that the SPI/PVA films were partially crystalline materials with peaks of 2θ = 20°. And, the addition of glycerol will insert the crystalline structure and destroy the blend microstructure of SPI/PVA. Differential scanning calorimetry (DSC) tests show that SPI/PVA blend polymers have a single glass transition temperature (T_g) between 80 and 115.0°C, which indicate that SPI and PVA have good compatibility. The tension tests show that SPI/PVA films exhibit both higher tensile strength (σ_b) and percentage elongation at break point (P.E.B.). Thermogravimetric analysis (TGA) and water solubility tests show that SPI/PVA blend polymer has more stable stability than pure SPI. All the results reflect that SPI/PVA/glycerol blend film provides a convenient and promising way to prepare soy protein plastics for practical application. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Role of Star‐Like Hydroxylpropyl Lignin in Soy‐Protein Plastics

Summary: Star‐like hydroxypropyl lignin (HL) was compounded into soy protein isolated (SPI) to develop a potential biodegradable plastic with better mechanical performance than pure sheet‐SPI. The structure and properties of the composite materials were characterized by WAXD, DSC, SEM, TEM and tensile tests. The addition of just 2 wt.‐% HL resulted in tensile strength (σ_b) of 16.8 MPa, 2.3 times that of pure sheet‐SPI, with no accompanying decrease in elongation at break as a result of strong interaction and with good miscibility among components. As the HL content increased, the HL molecules could self‐aggregate as oblate supramolecular domains, while the stronger interactions between HL and glycerol resulted in the detaching of glycerol from the SPI matrix. It can be concluded that the insertion of HL as single molecules into the SPI matrix would provide materials with optimum mechanical properties. Compared with other lignin/SPI composites, the stretching chains on HL play a key role in the improvement of mechanical properties because of a stronger adhesion of HL onto the SPI matrix as well as the interpenetration of SPI into supramolecular HL domains.

Schematic illustration of the supramolecular domain created by the aggregation of hydroxypropyl lignin, which can interpenetrate with soy protein isolate.     

Effects of lignin as a filler on properties of soy protein plastics. II. Alkaline lignin

Blend plastics based on soy protein isolate (SPI) strengthened with alkaline lignin (AL) in the weight ratio of 10:0 to 5:5 were prepared with 40 wt % glycerol as a plasticizer by compression molding. The structure and mechanical properties of the blends were investigated by wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamical mechanical thermal analysis (DMTA), and tensile tests. The results indicated that the introduction of AL could effectively increase the tensile strength and Young's modulus, thermal stability, and elongation of the compositive plastics when the AL content ranged from 10 to 20 parts. Moreover, the blend plastics containing 50 parts AL exhibited maximum tensile strength (1.98 MPa) and much higher than that with the SP–AL0 sheet with AL alone (0.89 MPa). In addition, tests of water absorption proved that the introduction of hydrophobic AL effectively reduced water absorption and, hence, decreased water sensibility. Therefore, AL, a relatively low‐cost filler, plays a major role in enhancing the strength and water resistivity of soy protein plastics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3291–3297, 2003     

Morphology and properties of soy protein plastics modified with chitin

A series of bioplastics from isolated soy protein (SPI) and chitin (CH) was prepared with glycerol as a plasticizer by blending and compression molding. Their morphology and properties were investigated by wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamical mechanical thermal analysis (DMTA), scanning electron microscopy (SEM), and tensile and water‐absorption tests. The added CH as a filler cannot strongly interact with SPI molecules and, hence, this results in phase separation in blends. However, the rigid nature of the CH molecules enhanced the tensile strength and Young's modulus, but decreased the breaking elongation of the materials. When the CH content was higher than 10 wt %, the water absorption of the blends were obviously lower than that of the sheets without CH, resulting from the formation of a CH framework in the blends. Both soy protein and CH exhibit good biodegradability, biocompatibility, and bioactivity, and their composites may become a promising biomaterial. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3676–3682, 2003     

Effects of the molecular weight on the properties of thermoplastics prepared from soy protein isolate

Commercial soy protein isolate (SPI) was fractionated into four fractions by an acidifying method from pH 5.7 to 4.5 with 2M HCl. A mixture of SPI with glycerin (50 g/100 g of dry SPI) was compression‐molded to obtain thermoplastic sheets. The weight‐average molecular weight (M_w) of the fractions, the structure, and the mechanical properties of the thermoplastic SPI sheets were investigated with light scattering, IR spectroscopy, wide X‐ray diffraction patterns, differential scanning calorimetry, ultraviolet spectroscopy, scanning electron microscopy, and tensile testing. After heating compression, the SPI sheets were transparent and exhibited a smooth and homogeneous structure. Moreover, the crystallinity degree of the thermoplastic SPI was obviously higher than that of the premix before compression because of the formation of intermolecular hydrogen bonding. The M_w's of the fractions were 1.17 × 10⁵ to 3.21 × 10⁵, and they increased with increasing pH value in fractionation. The mechanical properties and water resistance (R) of the SPI sheets increased with increasing M_w of the SPI fractions. The tensile strength and breaking elongation of the SPI sheets with an M_w value of 3.21 ×10⁵ were 5.7 MPa and 135%, respectively, and the R value was 0.54 after immersion in water for 15 days. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3373–3380, 2001     

Blend membranes prepared from cellulose and soy protein isolate in NaOH/thiourea aqueous solution

We have successfully prepared a series of blend membranes from cellulose and soy protein isolate (SPI) in NaOH/thiourea aqueous solution by coagulating with 5 wt % H₂SO₄ aqueous solution. The structure and properties of the membranes were characterized by Fourier transform infrared spectroscopy, ultraviolet‐visible spectrometry, dynamic mechanical thermal analysis, scanning electron microscopy (SEM), transmission electron microscopy, and tensile testing. The effects of SPI content (W_SPI) on the structure and properties of the blend membranes were investigated. The results revealed that SPI and cellulose are miscible in a good or a certain extent when the SPI content is less than 40 wt %. The pore structure and properties of the blend membranes were significantly improved by incorporation of SPI into cellulose. With an increase in W_SPI from 10 to 50 wt %, the apparent size of the pore (2r_e) measured by SEM for the blend membranes increased from 115 nm to 2.43 μm, and the pore size (2r_f) measured by the flow rate method increased from 43 to 59 nm. The tensile strength (σ_b) and thermal stability of the blend membranes with lower than 40 wt % of W_SPI are higher than that of the pure cellulose membrane, owing to the strong interaction between SPI and cellulose. The values of tensile strength and elongation at break for the blend membranes with 10 wt % of W_SPI reached 136 MPa and 12%, respectively. The blend membranes containing protein can be used in water because of keeping σ of 10 to 37 MPa. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 748–757, 2004     

大豆分离蛋白/聚乙烯醇塑料的制备及性能研究

将聚乙烯醇（PVA）按不同比例与大豆分离蛋白(SPI)混合,采用丙三醇作为增塑剂,经模压成型制备SPI/PVA塑料,采用X射线衍射仪、动态热机械分析仪、差示扫描量热仪、万能电子拉力试验机、扫描电子显微镜等研究了SPI/PVA塑料的结构、形态和性能。结果表明,丙三醇增塑的SPI会出现微相分离,即出现富丙三醇微区和富蛋白微区,而PVA的加入主要破坏了SPI在富丙三醇微区的晶体结构,并使富丙三醇微区的玻璃化转变温度向高温方向偏移。PVA的加入还明显提高了SPI/PVA塑料的拉伸强度,当PVA含量为1份时,其拉伸强度比纯SPI塑料提高了41.5 %;PVA的加入对SPI/PVA塑料的吸水性也有明显改善,其24 h吸水率从134.86 %下降到77.38 %。     

Bio‐based polymeric resin from agricultural waste,neem (Azadirachta indica) seed cake,for green composites

Protein‐based polymeric resin has been developed from nonconventional and nonedible “neem seed cake (NSC)” that has very limited low‐value applications. Neem protein (NP), after extraction from defatted NSC, was used to prepare resin with two common plasticizers (glycerol and sorbitol). Properties of the NP resin sheets were evaluated as a function of plasticizer content. Increase of plasticizer content in NP sheets from 15 to 30% (w/w) enhanced fracture strain with a reduction in tensile strength, modulus, and thermal properties. Sorbitol‐plasticized NP sheets showed better mechanical and thermal properties in comparison to glycerol‐plasticized sheets. Effect of cross‐linking with glyoxal on the mechanical and thermal properties of sorbitol‐plasticized NP sheets was also investigated. Properties improved significantly at 10% (w/w) glyoxal content. Overall, with the enhanced properties of NP sheets, NP can be a viable alternative for edible protein‐based resin for making green composites. NP resin can also be used to replace some synthetic resins. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 10.1002/app.41291.     

Plasticization of soy protein polymer by polyol-based plasticizers

Soy protein isolate (SPI) was mixed with four polyol-based plasticizers and molded into plastics using a hot press. The plasticized SPI powder was evaluated for denaturation temperatures and denaturation enthalpies. The SPI plastics were studied for mechanical properties, glass transition temperatures, storage modulus, morphology, and water absorption. Thermal properties of the SPI plastics with propylene glycol were depressed to the largest degree, and the plastics with glycerol showed the largest strain at break, whereas plastics with 1,3-butanediol gave the highest tensile strength. The morphology of the fractured surface on the SPI plastics changed from brittle fracture for the unplasticized SPI to ductile fracture for the plasticized SPI. Water absorption of all the plasticized SPI plastics was lower than that of the unplasticized SPI plastics.     

Effect of coal filler on the properties of soy protein plastics

The influence of ultrafine coal filler (UFC) content on tensile properties, water absorption, and biodegradability of soy protein plastics were investigated. The addition of UFC in the soy protein plastics, with different content of glycerol as a plasticizer, was at different ratio varying from 10:0 to 6:4. Blend sheets of the soy protein composites were prepared by the compression molding processing. The results show that, with 23.08 wt % glycerol, the tensile strength and elongation at break for the soy protein sheet with coal filler (range from 5 to 30 parts) can be enhanced as compared with nonfilled soy protein plastics. Water resistance of the soy protein plastics improves with the increase in UFC content. The derivative thermogravimetry (DTG) curves indicate a double‐stage degradation process for defatted soy flour (SPF), while three‐stage degradation process for soy plastics and the soy protein composites. FT‐IR, XPS, and SEM were applied to study the interfacial interaction between coal macromolecules and soy protein molecules in UFC filled soy protein plastics. The results demonstrated that there is strong interfacial interaction in the soy protein plastics caused by the compression molding processing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3134–3143, 2006     

Effects of arm number on the properties of transparent elastomers prepared from styrene–butadiene block copolymer

A series of the SBS transparent elastomers were prepared from star‐shaped SBS having different arm number by solution‐casting. Their structure and physical properties were characterized by scanning electron microscope, ultraviolet spectrometer, wide‐angle X‐ray diffractometer, differential scanning calorimetry, dynamic mechanical thermal analysis, tensile testing, and contact angle measurements. The results revealed that the miscibility, optical transparence (T_r), tensile strength (σ_b), elongation at break (ε_b), and elasticity at low temperature of the star SBS increased with an increase of arm number. The six‐arm SBS having relatively high molecular weight exhibited a simultaneous enhancement of T_r (90% at 800 nm), σ_b (6.0 Mpa), and ε_b (1260%). This indicated that the SBS materials having six arms had higher transparence and elasticity than others. Moreover, the water contact angle on surface of the star‐shaped SBS film increased with an increase of arm number that is enhancement of hydrophobicity. Therefore, the relatively high arm number and molecular weight played an important role in the improvement of the miscibility and properties of the SBS sheets as a result of the compacted architecture of the hyperbranched molecules. This work provides a convenient way to obtain materials with both high transparence and elasticity by increasing the arm number. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 729–736, 2006     

Effect of uniaxial drawing of soy protein isolate biopolymer film on structure and mechanical properties

The effect of uniaxial drawing of biodegradable soy protein isolate (SPI) polymer film on mechanical properties was investigated to accelerate the efforts to develop SPI films with improved properties. The films containing 0–30 wt% glycerol were drawn uniaxially up to a draw ratio of 2.5. The mechanical properties of the SPI film increased significantly after uniaxial drawing. The tensile strength of the undrawn film (49.7 MPa) was approximately doubled by subjecting the film to uniaxial drawing to a D.R. of 2.5. Wide‐angle X‐ray diffraction and differential scanning calorimetry measurements did not show evidence of generation of a crystal phase in the drawn SPI films. ATR‐FTIR revealed that the protein film contained mainly α‐helix and β‐sheets secondary structures. Microwave molecular orientation analysis showed that birefringence increased with increasing draw ratios. Mechanical anisotropy of the SPI film via orientation of α‐helix and β‐sheets structure is thought to be responsible for the enhancement of mechanical properties with uniaxial drawing of the SPI films. POLYM. ENG. SCI., 47:374–380, 2007. © 2007 Society of Plastics Engineers.     

甲基丙烯酸缩水甘油酯对大豆蛋白塑料改性作用研究

用模压的方法制备了甲基丙烯酸缩水甘油酯(GMA)改性大豆分离蛋白质(SPI)塑料。表征了GMA改性SPI塑料的力学性能、耐水性,并分析了GMA与SPI之间的相互作用。结果表明GMA在模压过程中,环氧基与蛋白质分子间发生接枝和交联反应,同时自聚,在GMA含量较低时可以同时对SPI塑料起到增强和增塑作用,但是随着GMA含量增加,交联作用增强,塑料的断裂伸长率下降。     

Structure and properties of soy protein films plasticized with hydroxyamine

Two kinds of transparent films of soy protein were successfully prepared by plasticizing with diethanolamine (DEA) and triethanolamin (TEA). The films were hot pressed at 140°C and 20 MPa, and characterized with Fourier transform infrared spectroscopy, scanning electron microscope, ultraviolet–visible spectrometer, differential scanning calorimetry (DSC), thermogravimetric analysis, and tensile testing. The results indicated that films with triethanolamine plasticizers possessed better optical transmittance (more than 80% at 800 nm) than those with diethanolamine and glycerol. All of the sheets exhibited only one T_g in DSC curves. Moreover, the soy protein plastics with TEA had higher thermal stability and mechanical properties, as well as lower water uptake than those with DEA and glycerol, as a result of the strong interaction between TEA and protein molecules. The soy protein materials will be promising for the application in the fields of package and container, substituting for the nongreen polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal and mechanical properties of plasticized poly(L‐lactic acid)

Acetyl tri‐n‐butyl citrate (ATBC) and poly(ethyleneglycol)s (PEGs) with different molecular weights (from 400 to 10000) were used in this study to plasticize poly(L‐lactic acid) (PLA). The thermal and mechanical properties of the plasticized polymer are reported. Both ATBC and PEG are effective in lowering the glass transition (T_g) of PLA up to a given concentration, where the plasticizer reaches its solubility limit in the polymer (50 wt % in the case of ATBC; 15–30 wt %, depending on molecular weight, in the case of PEG). The range of applicability of PEGs as PLA plasticizers is given in terms of PEG molecular weight and concentration. The mechanical properties of plasticized PLA change with increasing plasticizer concentration. In all PLA/plasticizer systems investigated, when the blend T_g approaches room temperature, a stepwise change in the mechanical properties of the system is observed. The elongation at break drastically increases, whereas tensile strength and modulus decrease. This behavior occurs at a plasticizer concentration that depends on the T_g‐depressing efficiency of the plasticizer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1731–1738, 2003