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This present study, to explore the value added utilization of canola meal, a main byproduct from canola oil industry. The canola meal was plasticized with glycerol/water mixture, denatured by the addition of guanidine hydrochloride (GHCL) were thermally processed in melt extrusion. The combined effect of plasticization and destructerization yields thermoplastic canola meal (TCM). The TCM was blend with PBAT and PBAT/PLA biodegradable polyester to fabricate new blend green materials. The new blend material blend properties were characterized by thermal (TGA, DSC), thermo mechanical (storage modulus and TanÎ´), and tensile, and Izod impact measurements.
The melt-compounded blends of TCM with biodegradable polyesters give new ductile bioplastics. The higher tensile, flexural and modulus values were obtained using TCM with biodegradable blends of PBAT/PLA. This study is attributed to the plasticization effect of glycerol to its small size which helps in its insertion and positioning within the protein structure in order to make it more compatible with polymer system.
Keywords: Thermoplastic canola meal, PBAT, PLA and Biocomposite
*Corresponding author. Tel.:+1 519-824-4120. Extn. 56664
Email address: [email protected] (Amar Mohanty)
In recent years, sustainability, environmental concerns and green chemistry have played a vital role in guiding the development of the next generation of materials, products and technology. The majority of plastics come from petroleum resources and does not degrade in environments and causing serious to terrestrial and aquatic habitat (www.plasticseurope.com, 2011). In this concern, renewable agriculture and biomass feedstocks have shown much promise to replace petroleum feedstock, without competing with food crops (Von Braun, 2007).
Canola meal is the main by product of the canola oil industry. Canola meal is the second largest protein meal produced in the world, after production of soybean meal (USDA, 2012). It is currently used for relatively low-value animal feed (Bell, 1993). Canola meal contains 34-38% protein, although canola protein possesses a well-balanced amino acid composition. Due to its high content of storage proteins, canola meal has potential to be used in a variety of potential industrial product applications such as adhesives, plastics and composites (Manamperi et al., 2010b; Mooney, 2009).
Proteins are natural thermoplastic polymers made up of various amino acids that are readily available for wide range of molecular interaction (Chen et al., 2008; Mo et al., 1999; Zhang et al., 2001). The functional properties of canola protein based plastic can be prepared by either melt processing or solvent processing. Melt processing has been widely used in the polymer industry because it has many advantageous properties such as solvent-less, environment-friendly, and convenient processing. However, canola protein degrades at lower temperature during the melt processing, and it can be overcome by plasticization and destruction of canola meal (Mo et al., 1999). By incorporating plasticizers and properly controlling processing parameters, the proteins can be thermally processed with minimal thermal decomposition. This allows improved processability in thermoplastic formulation such as extrusion and injection moulding (Mangata et al., 2001). For effective plasticization, the plasticizers must have similar polarity to the proteins (Zhang et al., 1998). Plasticizers are added to proteins to reduce their processing temperature, by increasing molecular mobility and decreasing viscosity. Plasticizers act by reducing hydrogen bonding, van der Waals, or ionic interactions that hold polymer chains together, through forming plasticizer-polymer interactions. (Verbeek and van den Berg, 2010). Common plasticizers are used for industrial oil co-products based plastics, such as water, glycerol, ethylene glycerol, propylene glycerol, 1,2-butanediol, 1,3-butanediol, poly(ethylene glycol), sorghum wax, and sorbitol (di Gioia and Guilbert, 1999; Woychik et al., 1961). Another destructerization process is generally achieved by the usage of the chemical additives or mechanical forces, such as extrusion (Aithani and Mohanty, 2006). In this paper, guanidine hydrochloride (GHCL) and glycerol was used for destruction and plasticization of canola meal. Destructerization and plasticization methods are provided in the experimental section.
The bio-fillers is renewable and cheaper substitute for synthetic fibers, such as glass and carbon and have numerous advantages, such as low cost, low density, high toughness, acceptable specific strength properties, ease of separation and biodegradability. Many approaches have been used to address the problems of biobased filler based plastics. The blending approach helps in enhancing the material properties and water sensitivity of the canola based plastics (Manamperi et al., 2010a). In this paper, we report our results on a reactive extrusion process for production blends of other polymers with canola protein represent an important route to overcome the limitations. Furthermore, the processing of canola protein is almost same as that of many biodegradable polymers. Similarly, researchers have been worked on the blends of various biobased fillers, such as soy protein, DDGS, lingo cellulosic filler, with bioplasticsÂ by using the melt extrusion process techniques (Muniyasamy et al., 2013; Reddy et al., 2010; Yang et al., 2005; Zarrinbakhsh et al., 2011). Soy protein concentrate was blended with Copolyester in a twin screw extruder; this combination has resulted in highly interacting blends (Song et al., 2011). Several biodegradable polymers, such as poly(butylene succinate adipate) (PBSA), poly(3-hydroxybutyrate) (PHB), poly(butylene succinate) (PBS), and poly(lactic acid) (PLA), are increasing in various sector application such as automotive, packaging, agriculture, disposal items. In our studies, PBAT and PBAT/PLA blend was used to fabricate with TCM explore the mechanical, thermal properties for obtaining new greener materials.
PBAT is an aliphatic-aromatic polyester with properties comparable to many fossil-oil-based plastics, and it is easily biodegradable (Kijchavengkul et al., 2010)(Witt U,2001). It degrades within a few weeks with the aid of naturally occurring enzymes. PBAT is a flexible plastic designed for film extrusion and extrusion coating. In view of its high toughness and biodegradability, PBAT was considered a good candidate for toughening of PLA. PLA is a biodegradable and biocompatible crystalline polymer that can be produced from renewable resources. The properties of PLA are dependent on the ratio between the two enantiomers, D and L. PLA can show crystalline polymorphism, which can lead to different melting peaks (Quero et al., 2012). Both PBAT and PLA are biodegradable polymers, and are used in consumer products by several industrial sectors due to their biocompatibility, biodegradability and sustainability. They have comparable thermal and mechanical properties to those of some conventional plastics, and this has generated much interest in exploring their physical and processing properties for potential applications (Quero et al., 2012). The aim of this study was to investigate the plasticized using glycerol/water mixture, denatured by the addition of guanidine hydrochloride (GHCL) and the behavior of thermal, mechanical properties of thermoplastic canola meal based plastics.
2. Experimental Section
The canola meal was obtained from the local canola oil processing industry- canada. The PBAT, poly(butylene adipate-co-terephthalate) pellets - Biocosafe 2003 were obtained from Zhejiang Hangzhou Xinfu Pharmaceutical Co., Ltd., China. The PLA pellets - Ingeo were obtained from Nature Works, USA. Glycerol (99.9% grade) was obtained from Sigma-Aldrich-canada. Guanidine Hydrochloride (GHCL) was obtained from Fisher Scientific - Canada.
2.2. Preformulation and plasticization of thermo plastic canola meal (TCM)
The TCM was prepared in two steps. The initial step involved destructerization and plasticization of canola meal. During the destructerization process of canola meal, 7.5phr GHCL was dissolved in 10phr water and were premixed in canola meal 70% (wt %) for 30â€‰min in a kitchen mixer. During the plasticization of destructerized canola meal, glycerol 30% (â€‰wt%) was mixed in a kitchen mixer and kept for overnight at room temperature. The second step involved, this mixture was extruded at 120â€‰Â°C in a microcompounder (DSM Research, The Netherlands), which is a mixer with twin vertical co-rotating screws, with a length of 150â€‰mm,Â L/DÂ of 18, and a maximum capacity of 15 cm3. A residence time of 2â€‰min was maintained for this process. The extruded canola was collected and dried in a ventilated oven for 8â€‰h at 80â€‰Â°C. This material is referred to as TCM throughout the paper.
2.3 DSM processing of biocomposite materials
The TCM based PBAT and PBAT/PLA composite materials were prepared using a Micro 15-cc Twin Screw Compounder (DSM, the Netherlands), paired with a Micro 12-cc Injection Moulding Unit (DSM, the Netherlands). All composite samples were processed at 160Â°C, with a screw rotation speed of 100 rpm. Each batch was processed in the micro-compounder for 3 minutes prior to injection moulding. After three minutes, the samples were transferred to the injection molding unit using a cylinder, also heated to 160Â°C. Using the injection molder, tensile, flexural, impact and DMA samples were produced for each composite material, as well as neat PBAT. All processing materials were dried for 8 hours prior to processing, at 80Â°C in a ventilated oven to eliminate moisture from the material. After processing, all test samples were stored at room temperature, and characterized after 48 hours.
2.4 Mechanical properties
Tensile and flexural properties of the composites were measured by a Universal Testing Machine, Instron 3382, according to the ASTM D638 and ASTM D790 standards, respectively. System control and the data analysis were done using Blue Hill software. The notched Izod impact strength was measured with a TMI Monitor Impact Tester (model no. 43-02-01) according to ASTM D256, using a pendulum of 5 ft-lb.
2.5. Scanning Electron Microscopy (SEM)
The morphology of the TCM biopolymer blends was studied by SEM. The fractured samples from tensile testing were used for the morphological studies. Hitachi instrument model S-570 SEM (Hitachi High Technologies, Japan) was used to obtain the SEM images for the composite specimens. A gold palladium coating of 20â€‰nm in thickness was coated on cryo-fractured surfaces by using an Emitech K550, UK. The fractured surface of the samples was used to study the phase morphology.
2.6. Differential Scanning Calorimetry (DSC)
Heat flow as a function of temperature was studied using a differential scan-ning calorimeter (DSC Q 200, TA Instruments, Inc.) using the heat-cool-heat setting. Nitrogen was used as purge gas during the experiment. The data was collected by heating the specimen from âˆ’50 to 200 â-¦C at a constant heating and cooling rate of 10 â-¦C/min. The data were analyzed using Universal Analysis software (TA Instruments). All the thermal properties were obtained from the second heating run of the DSC curves.
2.7. Thermogravimetric Analysis (TGA)
Thermogravimetric analysis was carried out using a thermogravimetric analyzer (TA Instrument Inc Q500). The samples were scanned from room temperature to 800 â-¦C at heating rate of 20â-¦C/min in a nitrogen atmosphere.
2.8 Dynamic Mechanical Analysis (DMA)
A DMA Q800 from TA Instruments was used to evaluate the storage modulus of rectangular samples of 3.2 x 12.5 x 65mm3. The experiments were performed from -50 to 100Â°C with a ramp rate of 3 Â°C min-1. A dual cantilever clamp was used at a frequency of 1 Hz and oscillating amplitude of 15Âµm.
2.9 Fourier Transform Infrared spectroscopy (FT-IR)
A Thermo Scientific Nicoletâ„¢ 6700 FTIR spectrometer was used in attenuated total reflection infrared (ATR-IR) mode with a resolution of 4Â cmâˆ’1Â and a number of 32 scans per sample were used to obtain the spectra.
3. Results and Discussion
It is well known that canola proteins have complex macromolecular structures with different amino acids. Due to its strong intra- and intermolecular interactions make it difficult to process and blend with biopolymer. Various studies have been done on the interaction of GHCl with proteins, which revealed the reduction of denaturation and unfolding of the protein structure (Ahmad et al., 2005; Courtenay et al., 2009; Dunbar et al., 2008). Denaturation is the alternation of secondary, tertiary and quaternary structure in the protein. The GHCl forms cross link at different locations in the side chains and on the back bone of the protein molecule by means of hydrogen bonding and van der walls interaction (Dunbar et al., 2008).
The brittle nature of the canola protein based material necessities the use of plasticizers. Glycerol has been extensively studied as a plasticizer. The plasticization effect of glycerol is attributed to its small size which helps in its insertion and positioning within the protein network (Cuq et al., 1997) and thereby reducing the intermolecular forces and increasing the mobility of protein chains. The GHCL was used to break down the protein structure in order to make it more flexible and compatible with the other components of the polymer system.
In meal processing techniques, the plasticized canola meal was processed in a DSM microcompounder, as explained in the experimental section. Thermogravimetric analysis (TGA) was applied to investigate the thermal behavior of TCM. It is important to correlate the thermal behavior of pre-formulated canola with their composition. TGA results suggest that the pre-formulation treatment helped in improving the thermal stability of canola meal i.e. particularly the temperature range from 50 - 200 Â°C (Figure 1). Such observations are additional information to predict the thermal stability and processing temperature of the material of our main purpose of the study for the development of thermoplastic canola meal based biocomposite materials.
Figure 1. TGA traces of canoal meal (as received) and TCM (after modified).
3.1 Mechanical properties
Figure 2 show the tensile and flexural strength of TCM blended with PBAT and PBAT/PLA. It can be seen that the tensile strength of the TCM-PBAT is lower compared to that of TCM-PBAT/PLA blend, while percent elongation showed the opposite trend (Figure 2). PLA is well-known as a brittle polymer and was introduced into PBAT to balance the tensile properties of TCM-PBAT/PLA blends. As PLA content was introduced into the TCM-PBAT system, tensile strength increased, while percent elongation decreased, showing that the system was interacting (Figure 2 a, b, c) . It can be seen from the Figure. 2c with addition of PLA, there is a decrease in percent elongation values. With 10% PLA addition, the percent elongation value reduced from 194 MPa to 67 MPa compared to the PBAT-TCM blend, indicating the improved toughness in the blend. However, the tensile modulus and tensile strength values increased with PLA addition. Tensile strength and tensile modulus values were increased in this work for the canola meal-biodegradable polyester based composites.
The TCM-PBAT blend showed a tensile strength of 5.1 MPa and flexural strength of 4.5 MPa, with 40% loading of thermoplastic canola meal. By adding 10% PLA into the PBAT - TCM blend systems, the material became tougher. It is well known that percent elongation and tensile strength are a strong reflection of the interface state (Averous and Boquillon, 2004; Zhao et al., 2010). The observed tensile properties for TCM-based blends with polyesters show a decreasing trend in tensile strength. This indicates poor interfacial interactions between phases in these blends. However, the higher percent elongation values show a high ductility for the blends. The reason for such high ductility is due to a high level of which could have led to the improved chain mobility (Graiver et al., 2004; Reddy et al., 2010; Sue et al., 1997). These improved mobilities in the protein chains have led to specific interactions with polyesters, especially by the PBAT material. These blends did not have any compatibilizer, leading to the improved mechanical properties. Glycerol is a known plasticizer for canola meal based plastics, and helps in their processing, while reducing their tensile properties. The observed improvement in the properties of these blends could be due to two reasons; the high elasticity of the destructured canola meal, and the compatibility between the polyesters used. The synergistic effect of unfolding and destructurization of protein by GHCL and high shear forces during extrusion, following the plasticization by glycerol, has caused high mobility in the protein chains.
Impact energy is absorbed by the material through plastic deformations. In notched Izod testing, the notching center acts as the stress concentration point and facilitates the crack propagation for plastic deformation of the material after impact. The comparisons of the impact strength of blends are given in Figure. 2c. The impact strength and elongation of biocomposite samples decreased as the biomass content was increased.
Figure 2. Mechanical properties of TCM-PBAT and TCM-PBAT/PLA blends.
3.2. Surface morphology
The morphologies of the fracture surfaces were investigated using SEM, as shown in Figure 3a. TCM-PBAT shows irregular fracture surfaces of a polymer, containing some holes, whereas TCM-PBAT+PLA show no phase separation (Figure 3b). The plasticized and destructured canola protein is very much ingrained in the PBAT matrix. The decrease in tensile strength of the blend could be due to the very low tensile strength of canola protein itself. By adding PLA into the blends TCM-PBAT80+PLA20 (60-40) that canola encapsulated itself between the matrices. This easily explains the better tensile strength and low percent elongation when compared to that of the TCM-PBAT blend. The observed phenomenon explains the difference in compatibility of the destructured canola protein with PBAT and PLA. The reason for the observed morphology is that the domain kind of morphology of canola protein in the blends started reducing to fibrils with the addition of PBAT phase (Reddy et al., 2010). This kind of change in morphology was evident that, the tensile properties and impact strength of these blends as explained earlier. The higher amount of PBAT showed higher percent elongation and impact strength. This is due to the addition of the unrestricted protein chain mobility in these blends. Another factor that could have contributed to this type of behavior is the twin screw melt extrusion which could have led to the deformation of protein from droplet to fibril due to the significant elongation flow component. Also, it was observed by previous studies with addition of PCL to soy protein (Reddy et al., 2010), plastic flow improved and led to the improvement in the toughness of the blends.
Figure 3. SEM micrographs of canola blends a) TCM-PBAT (60-40); b) TCM-PBAT80+PLA20 (40-60)
3.3 Thermo gravimetric analysis (TGA)
In general, the thermal weight losses of agricultural biomasses were quite sensitive to temperature, with narrow decomposition ranges. The temperature corresponding to the onset of decomposition (Tonset) for a polymer and canola meal based blends is essential for evaluating their thermal stability (Figure 4 and Table 1). PBAT is more thermally stable than PLA. The addition of thermoplastic canola meal decreased the Tonset of the PBAT and PBAT/PLA blends. PBAT and PLA undergo hydrolytic reactions by abiotic factors, and thermally degrade to produce polymeric chains terminated with carboxyl and vinyl groups. The carboxyl end groups of the polyester catalyze the hydrolysis reactions. All of the neat polymers exhibited a single peak, indicating that the PBAT and PLA degraded in only one step. The addition of thermoplastic canola meal to the TCM-PBAT and TCM-PBAT+PLA matrix exhibited two step thermal degradation of biopolymer blend. The first derivative peak is the thermal degradation of thermo plastic canola meal at 212.3Â°C and the second peak is the thermal degradation for PBAT and PLA at 410.2 Â°C. All the biocomposites had a 13% weight residue increase with increasing biobased content, shown in Table 1.
Figure 4. TGA traces of a) neat PBAT, neat PLA and TCM b) PBAT-TCM and PBAT/PLA-TCM blends
Table 2. TGA results of degradation temperature of neat PBAT, neat PLA, TCM and their canola meal based composite materials.
T onset (Â°C)
Maximum degradation temperature (Â°C)
Residue weight (%) at 600Â°C
T onset (Â°C) - 5% weight loss. CM- canola meal; TCM- thermoplastic canola meal.
3.4 DSC analysis
Table 3 shows the thermal behavior for the blends with different compositions. DSC scans identified the glass transition phase, crystallization and melting behaviour for the blends studied. By adding plasticized canola meal to the PBAT matrix, there was increase in the melting and glass transition temperature (Table 3). This result was probably due to the small, fine particles of canola meal is acting as a nucleating agent (Averous and Boquillon, 2004). In contrast, results showed a decreased Tm and Tg in the PBAT/PLA blend with the addition of canola meal. This result is due to the PLA acting as a suppressor in the melting behavior of the PBAT matrix (Averous and Boquillon, 2004). On the other hand, the DSC curves of PBAT90/PLA10 blends exhibit two Tg values, which indicate that these blends are immiscible systems. This is probably due to the small, finely dispersed PLA crystals acting as nucleating agents in PBAT (Averous and Boquillon, 2004; Kumar et al., 2010). However, the addition of TCM to the PBAT/PLA sample resulted in a decrease of the PLA melting and glass transition temperature. In this study, the Tm of PBAT did not change significantly, except in TCM-PBAT from -121.5 to -125.1 (Table 3). This result suggests that the interfacial interaction between the polymer and blends might imply the formation of a more stable structure, perhaps due to increased movement of the polymer segments that facilitate polymer chain mobility.
Table 3. DSC results of PBAT, PLA and their canola meal based composite materials.
Tm 2 (Â°C)
Tm 1 - melting temperature of PBAT; Tm 2 - melting temperature of PLA; Tg 1 - glass transition temperature of PBAT; Tg 2 - glass transition temperature of temperature of PLA; Tc - crystallization temperature of PLA.
3.5 Dynamic mechanical analysis
DMA reveals the amount of energy stored in a material as elastic energy and amount of energy dissipated during mechanical strain, which strongly depends on the geometric analysis and level of dispersion of fillers and fibers within the matrix. The temperature dependencies of virgin PBAT, PBAT/TCM, and TCM-PBAT/PLA biodegradable composites are represented in Figure 5a. In the case of biodegradable canola protein composite, a significant increase in storage modulus compared to neat biodegradable polymer was observed over the temperature range from -50 Â°C to 100 Â°C. At the low temperature of -20 Â°C, the polymer matrix TCM-PBAT/PLA is slightly increased compared to the neat PBAT, and PBAT/TCM (60/40). This shows that biocomposite are in glassy state. The PBAT-TCM composite showed similar storage modulus at that of the neat PBAT matrix which reveals a lack of polar interaction between PBAT and TCM. The Tg of neat PBAT matrix corresponds to the lower temperature of its transition region (-32Â°C). The incorporation of TCM into the matrix resulted in a lower Tg of the matrix up to -35.1Â°C. Further addition of TCM-PBAT/PLA shows shifts in the Tg to comparatively higher temperature to -34.7Â°C of PBAT and Tg of PLA from 61.3 to 45.2Â°C. This indicates an enhancement of the interfacial adhesion between the filler and the biodegradable polymer matrices (Figure 5b).
Figure 5. a) Storage modulus and 5 b) Tan delta thermoplastic canola meal based composite materials.
3.6 FT-IR analysis
The combined effect of glycerol and GHCL has allowed for the production of canola meal-based bioplastics using melt extrusion. The denaturation of canola protein by GHCL was confirmed by FTIR (Figureure 6), where it was observed that the strong peak for the amide group, around 1626cm-1, in canola meal shifted to 1649cm-1, indicating hydrogen bonding. This phenomenon is likely responsible for the improvement of the mechanical properties of the protein based blends (Reddy et al., 2010). The obtained thermoplastic canola meal was used to blend with polyesters, i.e., PBAT and PLA individually and in hybrids.
Biodegradable thermoplastic canola meal-reinforced PBAT/PLA composites have been successfully prepared via melt processing. Preformulation and plasticization techniques provided better dispersion and improving the properties. The interfacial adhesion between filler and matrix was observed using SEM. The biocomposite materials analysis using DSC and TGA showed some synergistic characteristics between the TCM and polymer matrix. DMA results revealed that the dispersion of the filler in the polymer matrix substantially enhanced the storage modulus and TanÎ´. Structural analysis also further confirmed that thermoplastic canola protein plasticization and the destruction of biofiller helps for the formation of hydrogen bonding.
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