Polycaprolactone and acylated soy protein isolate to tune the features of brown seaweed biocomposites

doi:10.21203/rs.3.rs-2951783/v1

Download PDF

Research Article

Polycaprolactone and acylated soy protein isolate to tune the features of brown seaweed biocomposites

https://doi.org/10.21203/rs.3.rs-2951783/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Invasive brown seaweed Rugulopteryx okamurae (RO) can be used as basis of biocomposites with different polymers, such as polycaprolactone (PCL) or acylated soy protein isolated (SPIa). The addition of PCL can strengthen the biocomposite and the elastic modulus (E') goes from ~ 110 MPa to ~ 250 MPa. Nevertheless, when SPIa is added, a softening takes place, leading to E’ values around 40 MPa. The addition of PCL or SPIa induces a greater deformability in the systems, with a maximum deformation (~ 2.25 or ~ 23%) for a 70/30 or 25/75 ratio, respectively. The presence of PCL reduces the absorption of water, while SPIa produces a substantial increase to the point of obtaining superabsorbent materials at a 25/75 ratio (~ 2450 wt.%). In conclusion, the adequacy of the seaweed materials for different applications can be modulated through the addition of an adequate filler.

<em>Rugulopteryx okamurae</em>

composites

seaweed

soy protein

PCL

Rugulopteryx okamurae (RO) is an invasive brown seaweed original form northwestern Pacific Ocean, where water is warm [1], just like that of the Mediterranean Sea, where native species have been displaced by the RO due to its great capacity for adaptation [2]. The presence of RO on the seabed of the Strait Natural Park in 2020 was around 85–96% [3]. Apart from the damage to the ecosystems, significant bioaccumulation occurs on the coasts once the seaweed dies, to the point that around 5,000 tons were collected on the beaches of Ceuta between 2015 and 2016 [4]. This situation led to the inclusion of this species of macroalgae on the Spanish Catalogue of Invasive Species on 1 December 2020 [2], being also expected to stablish also in Portugal, Italy, Greece, Croatia, Slovenia, Cyprus and Malta [5].

Seaweed has some applications in industry. For example, their fatty acids can be used for biofuel [6], and some pigments are used in pharmaceutical and animal feed [7]. However, polysaccharides are the most used component in industry. Some polysaccharides like alginates, agar or fucanes (or fucoidan) are used these days on human and animal feed, cosmetics and pharmaceutical [8–10]. More recently, bioplastics based on seaweed have been developed due to their ease to be processed and to produce biofilms and bio-packaging [11, 12].

Poor mechanical properties displayed by some of these seaweed-based plastics can be improved through the addition of fillers. Composite materials are made from two or more polymers with different physical and chemical characteristics that, when combined, make up a single material with suitable properties. The polymer and materials that make up the composite are known as matrix and reinforcers, respectively [13]. Composite materials has been used since prehistory, where vegetable fibers were used as a reinforcing material in bricks [14]. More recently, in the 1940s, Henry Ford developed a plastic-panelled car with soybean, wheat, hemp, flax and ramie among other ingredients to obtain a durable, economical and simple to manufacture chassis [15]. The use of renewable materials, such as sawdust and fibers, in composites was introduced as a way to reduce the dependence on fossil fuels in the plastic industry, due to their low price and abundance. The use of these “eco-composites” or “green composites” has several advantages when compared to conventional plastics. The first and most obvious is the reduction of non-biodegradable waste and pollution as they are made from biodegradable material. Another advantage is the reduction in the use of pure materials, which can lower production costs by using initially waste material as part of the composite [16].

Polycaprolactone (PCL) is an aliphatic biodegradable and environmental-friendly polyester with a wide range of uses (biomedicine in tissue engineering, drug delivery or food packaging among others [17, 18]). Its stability, miscibility and hydrophobicity make it a good component when biocomposites are processed, increasing the stress and rigidity of the products [18, 19]. Moreover, its low glass transition (T_g= -60 ºC) and melting temperature (T_m= 60ºC) ease its processability through injection molding [20].

Soy protein isolate (SPI) is a cheap and available by-product from the soybean oil industry, which have already been demonstrated to be a suitable component of plastic materials [21], as SPI bioplastics possess optimal viscoelastic properties which are comparable to those of conventional plastics [22]. The acylation of SPI adds COO⁻ groups that improve the water absorption capacity [23], which can be interesting in the production of green superabsorbent materials, with applications in the diapers or personal care sector.

Both SPI and PCL are biodegradable polymers which potential as fillers of seaweed materials is considered in this study. These polymers have already been processed through injection molding for the production of bioplastics, such as the one proposed by Cuadri et al. [24] for functionalized soy protein, or the crayfish protein-PCL biocomposites produced by Felix [25]. Even if composite materials have been obtained by using natural biopolymers (e.g., albumen, soy) [26], biodegradable synthetic polymer (e.g., PCL) [25] or even inorganic particles (e.g., Montmorillonite) [27], to the best of our knowledge, there are not results of seaweed materials reinforced neither by SPI nor PCL.

The aim of this work is to obtain two different biocomposites using RO as matrix and including either acylated SPI (SPIa) or PCL. The active matter/glycerol ratio was kept constant at 50/50, assessing the effect of different RO/PCL and RO/SPI ratios (RO/PCL ratios: 100/0, 90/10, 80/20 and 70/30; RO/SPIa ratios: 100/0, 75/25, 50/50 and 25/75). Subsequently, bioplastics were processed by injection molding at 120ºC, and they were characterised by DMA, tensile tests, water absorption capacity and SEM microscopy.

2.1. Materials

The Rugulopteryx okamurae (RO) seaweed used to produce the composites was live seaweed collected from the seabed of the Bay of Algeciras and subsequently freeze-dried. It was supplied by the Andalusian Institute for Agricultural, Fisheries and Organic Production Research and Training (IFAPA, Puerto Real, Spain). The freeze-dried seaweed was grounded on a kitchen blender (Mambo10070, CECOTEC, Valencia, Spain) at maximum speed, obtaining a particle size diameter D [4, 3] within the range of 10 to 100 µm for most particles (~ 90%).

Polycaprolactone (PCL) was used as part of the composite as polymer (Sigma-Aldrich, San Luis, Missouri, U.S.A.) with an average molecular weight of 80 kDa.

Soy protein isolate (SPI) (SUPRO 500E IP, Leper, Belgium) was supplied by PROANDA (Proveedora Andaluza, S.L., Sevilla, Spain). The acylation of SPI was carried out according to a modification of the method proposed by Hwang et al. [28, 29] and modified by Cuadri et al. [23]. Succinic acid (SA) was added to a 4 wt.% SPI and distilled water solution to obtain a 0.12 SA/SPI ratio. After this, the solution was left stirring for 1 hour, making sure that the pH remains between 7.5 and 8.5 by adding the necessary amount of a 3.0 NaOH solution. After 1h, 3.0 N HCl was added to adjust pH to 7 to stop the reaction. The SPI solution was dialyzed against distilled water for three days, changing water when necessary to remove salts from SA. Finally, acylated SPIs were freeze-dried with a Teslar LyoQuest (Teslar, Life Science Solutions, Madrid, Spain), obtaining the final SPIa flour. Glycerine (Gly) was used as plasticizer (Panreac Química, S.A., Castellar del Vallès, Spain).

2.2. Methods

2.2.1 Sample Preparation

A two-step processing method has been followed to obtain the final bioplastics: (i) active matter (RO, PCL, SPIa) and plasticizer (Gly) were mixed in a two-blade counter-rotating batch mixer Haake Polylab QC (ThermoHaake, Karlsruhe, Germany) at 50 rpm and 60 ºC for PCL composites or room temperature for SPIa composites until homogeneity (5 min). Bioplastics at 90/10, 80/20 and 70/30 RO/PCL ratios as well as 75/25, 50/50 and 25/75 RO/SPIa ratios were always obtained keeping a 50/50 biomass/Gly ratio, as PCL does not require plasticizer to be processed; (ii) Blends were injected in a Minijet II (ThermoHaake, Karlsruhe, Germany) using same conditions proposed by Álvarez-Castillo et al. [30]. The processing conditions were cylinder temperature of 60ºC, a mould temperature of 120 ºC, injection pressure of 500 bar (10 s) and holding pressure of 200 bar (140 s), obtaining 1 x 10 x 60 mm³ probes.

2.2.2. Rheological Characterization of Composites Blends

Composite blends were analysed by dynamic mechanical thermal analysis (DMTA) using a DMA850 (TA Instruments, Wakefield, MA, USA) in compression mode. Frequency tests, from 0.1 to 10 Hz at a constant temperature of 25 ºC, and temperature ramp tests, from 0 to 180 ºC at a constant frequency of 1 Hz, were performed. Both tests were carried out within the linear viscoelastic region, previously determined by strain sweep tests at 1 Hz. 15 mm diameter parallel plates geometry was used for DMTA tests.

2.2.3. Characterization of the Composite Bioplastics

Rheological measurements

Rectangular probes (60 mm x 10 mm x 1 mm) of biocomposites were analysed in the DMA850 (TA Instruments, Wakefield, MA, USA). Frequency sweep tests, from 0.1 to 10 Hz, at a constant temperature of 25 ºC, and temperature ramp tests, from 0 to 180 ºC, at a constant frequency of 1 Hz, were performed within the linear viscoelastic region, previously determined by strain sweep tests at 1 Hz. DMA tests were performed using a tension clamp geometry.

Tensile Properties

Uniaxial tensile tests were performed using rectangular probes (60 mm x 10 mm x 1 mm) according to the standard ISO 527-2 [31] and at a constant elongation rate of 1 mm·min^− 1 and room temperature in a RSA3 (TA Instruments, MA, USA) to obtain stress-strain curves. From these curves, three mechanical properties were determined: Young’s modulus (E), maximum stress (σ_max) and maximum strain (ε_max).

Water Uptake Capacity

Water uptake capacity (WUC) was determined following a three stages method described by Cuadri et al. [32]. First, bioplastic samples were dried at 50 ºC for 24 h and weighed (w₁). After that, dried samples were immersed in 100 mL of deionized water for 24 h and weighed (w₂). Finally, samples were lyophilized for 24 h and weighed (w₃). WUC and soluble matter loss (SML) can be estimated using equations 1 and 2.

$$WUC \left(\%\right)=\frac{\left({w}_{2}-{w}_{3}\right)}{{w}_{3}}.100 \left(eq. 1\right)$$

$$SML \left(\%\right)=\frac{{(w}_{1}-{w}_{3})}{{w}_{1}}.100 (eq. 2)$$

Scanning Electron Microscopy (SEM)

After WUC, freeze-dried samples were cut into small pieces (~ 2.5 mm), gold coated and examined by SEM with a ZEISS EVO microscope (Oberkochen, Germany), employing a beam current of 18 pA at a working distance of ~ 8 mm. The acceleration voltage was of 10kV. Images obtained were analysed by ImageJ (Bethesda, MD, USA).

Statistical analysis

STATGRAPHICS Centurion XVIII software (The Plains, VA, USA) was used to carry out the statistical analysis by ANOVA tests. All measurements were carried out at least in triplicate and significant differences (p < 0.05) was reported in selected parameters by superscript letters.

3.1. Blends

Rheological properties during mixing

Figure 1 shows the increase of torque and temperature with mixing time for biocomposites studied containing different ratios of RO/PCL (100/0, 90/10, 80/20 and 70/30) (Fig. 1A) or of RO/SPIa (100/0, 75/25, 50/50 and 25/75) (Fig. 1B). Generally, a maximum torque value is observed in the initial stage of mixing, followed by a decrease until reaching a plateau zone. This behavior is similar regardless of the additive used, except for the system with a RO/PCL ratio equal to 70/30 where the torque continues increasing until a plateau region is reached, not observing any maximum value. This behavior is similar to that found by Felix et al. [33] for SPI plasticized with glycerol and sorbitol, where sorbitol was added as a solid, which may suggest that the 70/30 RO/PCL blend may have a predominant solid behavior. It should be highlighted that when the percentage of PCL in the blend is increased (Fig. 1A), the plasticizer content in the mixture is lower, detecting an increase in torque and temperature. By reducing the plasticizer, the free volume in the blend is reduced, generating a greater friction between the polymer chains and, therefore, a higher increase in temperature [34]. On the other hand, when SPIa is used as additive in the biocomposites (Fig. 1B), a decrease in torque and lower rise in temperature (ΔT) is observed, being the torque for all the RO/SPIa composite systems eventually around 1 N·m. Contrary to PCL, it seems that SPIa promotes the fluid behavior of these samples. ΔT increases at the beginning of the mixing process, finally reaching a constant value when the plateau is achieved in torque. Similar results were obtained for RO/Gly systems not containing SPIa, where the higher the seaweed content in the mixture, the higher the value for torque and temperature [35]. Therefore, the highest ΔT (30ºC) is found for the system 70/30 RO/PCL due to the higher torque values achieved associated to the lower glycerol content, which leads to a higher mechanical energy dissipation [36]. Notwithstanding, it should be noticed that the mixing process of biocomposites containing PCL started at 60 ºC since that is the melting point of PCL, as previously done in works where PCL was processed with other biopolymers [25, 37].

Dynamic Mechanical Thermal Analysis (DMTA)

Figure 2 shows the evolution of viscoelastic moduli (E’ and E’’) with temperature (from 0 to 150 ºC) for the reference system containing only the plasticizer as additive (RO/Gly) and selected biocomposites (RO/PCL 70/30 and RO/SPIa 25/75).

A predominantly elastic behaviour is observed within the entire range of temperature studied, and the addition of the polymers (PCL and SPIa) as additives increased the elastic modulus of the materials obtained, improving the mechanical behaviour of the samples. E’ is always above E’’, even after PCL is melted (i.e., above 65 ºC). Thus, RO avoids the complete melting of the RO/PCL material, while PCL improves the viscoelastic properties of the composite developed. However, all the systems evaluated exhibited a certain dependence of the viscoelastic moduli with temperature. For the RO/SPIa systems there is a decrease in elastic modulus until a minimum at 65–70 ºC. This minimum presumably corresponds to a glass transition of SPIa as in the results obtained by Cuadri et al. for SPIa/Gly hydrogels [23]. Materials containing only RO as polymer exhibited a thermo-setting potential at high temperatures (i.e., above 75 ºC), which confirms the lack of interactions during the mixing stage as well as its ability to reinforce is microstructure by processing [35, 38]. Similar results have been found for other systems, such as crayfish or albumen exhibiting properties that made them suitable for further processing [39, 40].

3.2. Injection molded biocomposites.

Dynamic Mechanical Thermal Analysis (DMTA)

Figure 3 shows the DMTA tests carried out from 0 to 180 ºC for the bioplastics made from RO/PCL at four ratios (100/0, 90/10, 80/20 and 70/30) (Fig. 3A) and RO/SPIa at four ratios (100/0, 75/25, 50/50 and 25/75) (Fig. 3B). There is a general decrease in the value of elastic moduli (E’) of both composites when heating, which implies a softening of the bioplastics that is caused by a disruption of the secondary interactions (e.g., Hydrogen bonds). The fact that E’ decreases continuously during the DMTA tests for all samples reveals a lack of thermosetting potential to be achieve if the molding temperature would be to be increased further. Only the reference system containing only RO as biomass shows a slight increase in the viscoelastic moduli at the higher temperatures analysed. Moreover, the increase in the values of elastic moduli from blends to biocomposites of about one or two orders of magnitude, depending on the RO/filler ratio, implies that the temperature and pressure conditions during the injection molding stage was effective to achieve an important strengthening of the materials than just a mixing stage. In addition, this result also confirms the suitability of the processing technique used to obtain these materials.

An inflection point can be observed at 60 ºC in Fig. 3A, which is not observed in Fig. 3B, and corresponds with the melting point of PCL [41]. In this case, higher content on PCL resulted in higher elastic modulus (E’) at lower temperatures. Moreover, there is a slight inflection point for the RO/SPIa systems around 55–70 ºC, which may correspond to a glass transition of the sample. This thermal event was already observed by Fernández-Espada, L. et al [22] for SPI based bioplastics, and by Cuadri et al. [24] for functionalized soy protein bioplastics (SPIa). Please notice that the application of these composites is more restricted when adding PCL due to its thermal instability beyond its melting point (60 ºC), resulting in a breaking of bioplastics before 180 ºC in most cases, as already observed by Felix et al. [25] for crayfish-PCL composites. However, SPIa composites can resist higher temperatures.

Figure 4 shows the E’ at 1 Hz (E’₁) and the slope of E’ versus frequency of the injection molded bioplastics as a function of the PCL (Fig. 4A) and SPIa (Fig. 4B) content. Figure 4A shows an increasing trend in the value of the E’_1Hz in the RO/PCL systems when the amount of PCL increases. This result may involve a greater interaction between the polymeric chains since plasticizer decreases as the PCL ratio increases. This solid-like behavior of PCL on composites produces a more rigid structure. Furthermore, these lower interactions agree with the decrease in the slope when the amount of PCL in the mixture increases, which implies a lower dependence between the elastic modulus and the frequency under these conditions (i.e., higher relaxation time) [42].

On the other hand, when the dependence of the E’_1Hz value on the RO/SPIa ratios is analysed (Fig. 4B), a general tendency onto lower values is observed as SPIa content is increased. When the RO/SPIa ratio percentage goes from 100/0 to 25/75, a decrease of interactions between the biopolymers is deduced. As the presence of SPIa promotes a fluid-like behaviour it produces a more deformable structure and, therefore, less rigid. In this case, the slopes do not vary greatly with the SPIa content, especially when compared to RO/PCL systems (Fig. 4A), where a continuous decrease is detected, which may be related to the relatively low melting point of PCL.

3.3. Tensile tests

Figure 5 shows the stress-strain curves obtained by the RO/PCL composites (100/0, 90/10, 80/20 and 70/30) (A) and the RO/SPI composites (100/0, 75/25, 50/50 and 25/75) (B) studied. All systems show an initial linear elastic region from which Young’s modulus, E, can be determined at relatively low strain values where exclusively linear elastic deformation takes place. When strain is increased, slope begins to descend slightly, and plastic deformation of the material starts taking place, until a maximum value of stress (σ_max) is reached that, when exceeded, results in an abrupt decay of the slope, which corresponds to the breakage of the probe at a maximum strain (ε_max).

Rupture of probes seems to be different depending on the additive included in the biocomposites (PCL or SPIa). While a maximum in the stress is followed by an extended deformation before eventual rupture in RO/PCL systems, the RO/SPIa systems break more abruptly once σ_max is surpassed. Thus, in PCL composites, a local deformation is formed in the probe when maximum stress is reached, while that effect was no detected for SPIa composites. The increase in the concentration of plasticizer in RO/SPIa systems with respect to RO/PCL systems causes the rupture to go from a more plastic one at low deformations to a more elastic one at high deformations, as observed by Chang et al. [43].

Table 1 shows the values of the mechanical parameters (E, ε_max and σ_max) for the reference (50/50, RO/Gly), the RO/PCL composites (90/10, 80/20 and 70/30) and RO/SPI (75/25, 50/50 and 25/75) composites. The higher the values of ε_max and σ_max are obtained when higher amounts of PCL or SPIa is included in the formulation. As observed in Figure 5, there is an important increase in the value of σ_max at the highest PCL ratio, while in RO/SPIa composites, the biggest difference it is observed for ε_max value, increasing one order of magnitude at a 75% of SPIa (up to 22.8 ± 3.51). This increase in deformability should be mostly associated to the plasticizer. PCL as biopolymer acts increasing the mechanical properties (E, σ_max and ε_max) as its content increases. Biocomposites obtained get closer to the attributes of this biodegradable synthetic polymer, as the values obtained are moving towards the ones typically obtained for PCL [16]. On the other hand, when SPIa is used to form the RO/SPIa composite materials, the materials obtained increase their deformation at break. This behaviour could be related to the hydrophilic character of SPIa, which interact with the plasticizer used (Gly) better than PCL since both are highly hydrophilic [44]. Regarding Young’s modulus values (E), there are no significant differences observed between 100/0, 90/10 and 80/20 RO/PCL systems, and 100/0, 75/25 and 50/50 RO/SPIa systems, but there is a significant increase at highest percentages, i.e., 70/30 RO/PCL and 25/75 RO/SPIa systems, which is coherent with results obtained from DMTA tests. Similar results were obtained by Felix et al. [25] for crayfish/PCL composites and by Fernández-Espadas et al. for SPI/Gly bioplastics [22].

Table 1

Mechanical parameters (Young’s modulus (E), maximum stress (σ_max) and maximum strain (ε_max)) for bioplastics with different A) RO/PCL ratios (70/30, 80/20, 90/10 and 100/0) and B) RO/SPIa ratios (25/75, 50/50, 75/25 and 100/0). Different letters within a column indicate significant differences (p < 0.05)
	System	E(MPa)	ε_max (%)	σ_max (MPa)
Reference	100/0	0.40 ± 0.14 ^a	0.49 ± 0.07 ^a	0.088 ± 0.021 ^a
RO/PCL	90/10	0.47 ± 0.046 ^a	0.64 ± 0.14 ^a	0.12 ± 0.031 ^a
	80/20	0.28 ± 0.068 ^a	1.01 ± 0.14 ^b	0.17 ± 0.012 ^b
	70/30	1.64 ± 0.48 ^b	2.24 ± 0.66 ^c	1.70 ± 0.19 ^c
RO/SPIa	75/25	0.54 ± 0.16 ^a	2.21 ± 0.55 ^c	0.50 ± 0.086 ^d
	50/50	0.44 ± 0.064 ^a	9.06 ± 1.13 ^d	0.91 ± 0.084 ^e
	25/75	0.093 ± 0.058 ^c	22.8 ± 3.51 ^e	0.78 ± 0.15 ^e

3.4. Water Uptake Capacity

Figure 6 shows the water uptake capacity (WUC) and soluble matter loss (SML) of RO/PCL (100/0, 90/10, 80/20 and 70/30) (A) and RO/SPI (100/0, 75/25, 50/50 and 25/75) (B) composites. For PCL composite, there is an increase in WUC when decreasing the amount of PCL. This means that the greater WUC displayed by the systems with more RO on the mixture are also the ones with more Gly, which promotes the formation of porous in the structure and therefore, more absorption sites since Gly tends to pass to the aqueous part due to its hydrophilic behaviour [45]. The formation of pores enhancing interconnectivity is key for water uptake capacity [27, 46]. Thus, the diffusion of water molecules is restricted when PCL is in the structure of the material, resulting in a reduction in the final water adsorption. The fact that PCL is hydrophobic causes that it hiders the water diffusion thorough the protein matrix [47]. On the other hand, the increase of SPIa shown in Fig. 6B results in a greater capacity of water uptake, which could be attributed to the high hydrophilicity of SPIa [23]. Consequently, the ratio 25/75 (RO/SPI) leads to a WUC higher than 1,000%, and it can be considered a superabsorbent material (SAM), defined as materials which can absorb from 10 to100 times their own weight of water or fluids [48]. The great hydrophilicity of the SPIa in the composite is related to the acylation process carried out as pretreatment of SPI, which increases the number of COO⁻ groups in the SPI molecules, improving water absorption of the untreated SPI [23]. Cuadri et al. [23] already obtained superabsorbent materials using SPIa. However, the materials proposed reach similar values using a lower amount of soy protein (which has more industrial interest).

Regarding SML, there is an increase on its value when increasing amount of Gly on the RO/PCL formulation (which also involves a decrease of PCL in the formulation). This may occur because most of SML can be attributed to the solubilization of the glycerol, which has a great hydrophilic behaviour as mentioned before. However, there is also a loss of biomass apart from the glycerol since the mass loss is higher than the percentage of glycerol in the sample, as happened for bioplastics made from seaweed without reinforcement or [35]. In the case of RO/SPIa systems, the percentage of Gly does not vary between the different systems, and no significant differences are observed on SML values.

3.5. Scanning Electron Microscopy

Figure 7 shows the SEM images of all the freeze-dried composite systems after water immersion. Figures 7A, B and C corresponds to RO/PCL systems 90/10, 80/20 and 70/30 respectively. Figure 7D, E and F corresponds to systems RO/SPIa 75/25, 50/50 and 25/75 respectively. Figure 7C shows that as PCL content increases in the RO/PCL systems, the biocomposites surface gets smoother, displaying a lower number of pores in the 70/30 RO/PCL, which implies a smaller number of water absorption sites and interconnection. Greater roughness and cracks are observed at lower PCL contents (i.e., RO/PCL 80/20 and 90/10 systems) (Figs. 7B and 7A). These systems do not show great differences among them, which is in concordance with the fact that their water uptake capacities are quite similar and higher than that of the 70/30 RO/PCL system. Moreover, RO/PCL 70/30 system possesses a higher viscoelastic modulus, what implies a more resistant structure and rigidity, as observed in Fig. 5A, while 80/20 and 90/10 systems did not show large differences between them.

By contrast, RO/SPIa systems from Fig. 7 show more differences when their ratio is analysed. Thus, pore size increases when increasing SPIa percentage in the mixture, just as the WUC. Image F, corresponding to RO/SPIa 25/75 system has many imperfections and bigger pores than images E (RO/SPIa 50/50) and D (RO/SPIa 75/25). Comparing these results with the ones obtained in the DMTA test, RO/SPIa 25/75 is the one with the lower viscoelastic moduli (Fig. 3B) and the less rigid structure obtained in the tensile tests (Fig. 5B), confirming a more flexible structure that can provide a greater swelling ability when immersed in water.

The use of Rugulopteryx okamurae seaweed in the production of biocomposites allows obtaining materials by injection molding using a hydrophobic and hydrophilic additive (polycaprolactone and soy protein isolate acylated, respectively) as tuning additives, and glycerol as plasticizer. Increasing PCL when the PCL was present in the blends, bioplastics displayed higher values of viscoelastic moduli, rigidity and resistance, obtaining a maximum deformation (2.24 ± 0.66%) and stress (1.70 ± 0.19 MPa) at a 70/30 RO/PCL ratio. On the contrary, when increasing SPIa in the RO/SPIa systems, the materials obtained showed lower values of viscoelastic moduli, obtaining a more flexible and deformable structures, ranging from a deformation of 2.21 ± 0.55% to 22.8 ± 3.51% when increasing the RO/SPIa ratio from 75/25 to 25/75 respectively. Regarding DMA tests, both composites showed a softening when heating, although always prevailing the elastic behavior. The WUC tests confirmed the results already observed on the DMA and tensile tests. For RO/PCL, when increasing the amount PCL, a more rigid structure was obtained, with pores which can be used for water molecules to be adsorbed (as observed in SEM images). For RO/SPI systems, the opposite effect was observed. Thus, when increasing SPIa on the RO/SPIa system, the structure obtained had more pores, increasing its WUC, even achieving values of 2455 ± 449 wt.% for a RO/SPIa ratio of 25/75, which can be considered a superabsorbent material.

These results reveal how different formulations can be obtained when producing composites, that can be used to modulate the properties of materials based on the Rugulopteryx okamurae seaweed. These materials can be reinforced with PCL, obtaining hydrophobic and resistant materials; or with SPIa, obtaining hydrophilic and deformable materials. Additionally, the industrial application of this seaweed, which currently is an invasive specie and has low commercial value would lead to reduction of polluting emissions from conventional plastics industry and palliating the environmental burden caused by this invasive seaweed on the Mediterranean coasts.

Acknowledgements

The authors acknowledge the project PID2021-124294OB-C21 funded by MCIN/AEI/10.13039/501100011033/ and by “ERDF A way of making Europe” which supported this study, and the Andalusian government and the European commission for funding the contract of Ismael Santana through the Youth Employment Initiative (EJ5-13-1). The authors would also like to thank Ismael Hachero from the Andalusian Institute for Agricultural, Fisheries and Organic Production Research and Training (IFAPA, Puerto Real, Spain), for providing the seaweed used in this work, and also the CITIUS for granting access and assistance with the Microscopy service.

Data availability

The data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Agatsuma Y, Kuwahara Y, Taniguchi K (2005) Life cycle of Dilophus okamurae (Phaeophyceae) and its associated invertebrate fauna in Onagawa Bay, Japan. Fish Sci 71:1107–1114. 10.1111/j.1444-2906.2005.01070.x
García-Gómez JC, Florido M, Olaya-Ponzone L, de Rey Díaz J, Donázar-Aramendía I, Chacón M, Quintero JJ, Magariño S, Megina C (2021) Monitoring Extreme Impacts of Rugulopteryx okamurae (Dictyotales, Ochrophyta) in El Estrecho Natural Park (Biosphere Reserve). Showing Radical Changes in the Underwater Seascape. Front Ecol Evol 9. 10.3389/fevo.2021.639161
García-Gómez JC, Sempere-Valverde J, González AR, Martínez-Chacón M, Olaya-Ponzone L, Sánchez-Moyano E, Ostalé-Valriberas E, Megina C (2020) From exotic to invasive in record time: The extreme impact of Rugulopteryx okamurae (Dictyotales, Ochrophyta) in the strait of Gibraltar. Sci Total Environ 704:0–2. 10.1016/j.scitotenv.2019.135408
Ocaña O, Alfonso-Carrillo JM, Ballesteros E (2016) Massive proliferation of a dictyotalean species (Phaeophyceae, Ochrophyta) through the Strait of Gibraltar. Rev. Acad. Canar. Cienc. XXVIII, 165–170
Altamirano Jeschke M, Zanolla M (2019) Análisis de riesgos de la macroalga exótica Rugulopteryx okamurae. Ministerio para la Transición Ecológica y Reto Demográfico. 0, 69
Harun R, Singh M, Forde GM, Danquah MK (2010) Bioprocess engineering of microalgae to produce a variety of consumer products. Renew Sustain Energy Rev 14:1037–1047. 10.1016/j.rser.2009.11.004
Borowitzka MA (2013) High-value products from microalgae-their development and commercialisation. J Appl Phycol 25:743–756. 10.1007/s10811-013-9983-9
Berteau O, Mulloy B (2003) Sulfated fucans, fresh perspectives: Structures, functions, and biological properties of sulfated fucans and an overview of enzymes active toward this class of polysaccharide. Glycobiology 13:29–40. 10.1093/glycob/cwg058
Bixler HJ, Porse H (2011) A decade of change in the seaweed hydrocolloids industry. J Appl Phycol 23:321–335. 10.1007/s10811-010-9529-3
Food and Agriculture Organization of the United Nations The State of World Fisheries and Aquaculture 2014 (2014) ; ; ISBN 9789251082751
Lim C, Yusoff S, Ng CG, Lim PE, Ching YC (2021) Bioplastic made from seaweed polysaccharides with green production methods. J Environ Chem Eng 9. 10.1016/j.jece.2021.105895
Lomartire S, Marques JC, Gonçalves AMM (2022) An Overview of the Alternative Use of Seaweeds to Produce Safe and Sustainable Bio-Packaging. Appl Sci 12. 10.3390/app12063123
Versino F, López OV, García MA (2021) Green Biocomposites for Packaging Applications. Biocomposite Materials. Springer, Singapore, pp 1–30
Mwaikambo L (2006) Review of the history, properties and application of plant fibres. Afr J Sci Technol 7:121
Rusty D “Henry’s Plastic Car: An Interview with Mr. Lowell E. Overlay.” In; pp. 46–51
La Mantia FP, Morreale M (2011) Green composites: A brief review. Compos Part A Appl Sci Manuf 42:579–588. 10.1016/j.compositesa.2011.01.017
Akay O, Altinkok C, Acik G, Yuce H, Ege GK, Genc G (2022) Preparation of a sustainable bio-copolymer based on Luffa cylindrica cellulose and poly(ɛ-caprolactone) for bioplastic applications. Int J Biol Macromol 196:98–106. 10.1016/j.ijbiomac.2021.12.051
Acik B, Acik G, Erdemi H (2021) Synthesis and characterization of bile acid, poly (ε-caprolactone) and ÊŸ-lysine diisocyanate ethyl ester based polyurethanes and investigation of their biodegradability properties. Eur Polym J 146:110247. 10.1016/j.eurpolymj.2020.110247
Wróbel-Kwiatkowska M, Czemplik M, Kulma A, Zuk M, Kaczmar J, Dymińska L, Hanuza J, Ptak M, Szopa J (2012) New biocomposites based on bioplastic flax fibers and biodegradable polymers. Biotechnol Prog 28:1336–1346. 10.1002/btpr.1599
Malikmammadov E, Tanir TE, Kiziltay A, Hasirci V, Hasirci N (2018) PCL and PCL-based materials in biomedical applications. J Biomater Sci Polym Ed 29:863–893
Tian H, Wu W, Guo G, Gaolun B, Jia Q, Xiang A (2012) Microstructure and properties of glycerol plasticized soy protein plastics containing castor oil. J Food Eng 109:496–500. 10.1016/j.jfoodeng.2011.10.033
Fernández-Espada L, Bengoechea C, Cordobés F, Guerrero A (2016) Thermomechanical properties and water uptake capacity of soy protein-based bioplastics processed by injection molding. J Appl Polym Sci 133. 10.1002/app.43524
Cuadri AA, Bengoechea C, Romero A, Guerrero A (2016) A natural-based polymeric hydrogel based on functionalized soy protein. Eur Polym J 85:164–174. 10.1016/j.eurpolymj.2016.10.026
Cuadri AA, Romero A, Bengoechea C, Guerrero A (2017) Natural superabsorbent plastic materials based on a functionalized soy protein. Polym Test 58:126–134. 10.1016/j.polymertesting.2016.12.024
Félix M, Romero A, Martín-Alfonso JE, Guerrero A (2015) Development of crayfish protein-PCL biocomposite material processed by injection moulding. Compos Part B Eng 78:291–297. 10.1016/j.compositesb.2015.03.057
Martín-Alfonso JE, Félix M, Romero A, Guerrero A (2014) Development of new albumen based biocomposites formulations by injection moulding using chitosan as physicochemical modifier additive. Compos Part B Eng 61:275–281. 10.1016/j.compositesb.2014.01.057
Felix M, Martinez I, Romero A, Partal P, Guerrero A (2018) Effect of pH and nanoclay content on the morphology and physicochemical properties of soy protein/montmorillonite nanocomposite obtained by extrusion. Compos Part B Eng 140:197–203. 10.1016/j.compositesb.2017.12.040
Hwang DC, Damodaran S (1996) Equilibrium swelling properties of a novel ethylenediaminetetraacetic dianhydride (EDTAD)-modified soy protein hydrogel. J Appl Polym Sci 62:1285–1293. 10.1002/(sici)1097-4628(19961121)62:8<1285::aid-app19>3.3.co;2-5
Hwang DC, Damodaran S (1996) Chemical modification strategies for synthesis of protein-based hydrogel. J Agric Food Chem 44:751–758. 10.1021/jf9503826
Álvarez-Castillo E, Bengoechea C, Rodríguez N, Guerrero A (2019) Development of green superabsorbent materials from a by-product of the meat industry. J Clean Prod 223:651–661. https://doi.org/10.1016/j.jclepro.2019.03.055
ISO U-E Plastics - Determination of tensile properties - Part 2: Test conditions for moulding and extrusion plastics 2012, 527–2
Cuadri AAA, Romero A, Bengoechea C, Guerrero A (2018) The Effect of Carboxyl Group Content on Water Uptake Capacity and Tensile Properties of Functionalized Soy Protein-Based Superabsorbent Plastics. J Polym Environ 26:2934–2944. 10.1007/s10924-018-1183-x
Felix M, Carpintero V, Romero A, Guerrero A (2016) Influence of sorbitol on mechanical and physico-chemical properties of soy protein-based bioplastics processed by injection molding. Polimeros 26:277–281. 10.1590/0104-1428.0044
Jerez A, Partal P, Martinez I, Gallegos C, Guerrero A, Martínez I, Gallegos C, Guerrero A (2005) Rheology and processing of gluten based bioplastics. Biochem Eng J 26:131–138. 10.1016/j.bej.2005.04.010
Santana I, Félix M, Guerrero A, Bengoechea C (2022) Processing and Characterization of Bioplastics from the Invasive Seaweed Rugulopteryx okamurae. Polym (Basel) 14. 10.3390/polym14020355
Pommet M, Redl A, Morel MH, Domenek S, Guilbert S (2003) Thermoplastic processing of protein-based bioplastics: Chemical engineering aspects of mixing, extrusion and hot molding. In Proceedings of the Macromolecular Symposia; ; Vol. 197, pp. 207–218
Thongpin C, Buaksuntear K, Tanprasert T, Charoenta J (2020) Bio-based thermoplastic vulcanizates from natural rubber (bioplastic/NR). IOP Conf Ser Mater Sci Eng 773. 10.1088/1757-899X/773/1/012045
Jerez A, Partal P, Martinez I, Gallegos C, Guerrero A (2007) Preparation of bioplastic material from a protein matrix and plasticizer, useful for making biodegradable packaging, films and adhesives 17
Romero A, Cordobes F, Guerrero A (2009) Influence of pH on linear viscoelasticity and droplet size distribution of highly concentrated O/W crayfish flour-based emulsions. Food Hydrocoll 23:244–252. 10.1016/j.foodhyd.2008.02.001
Felix M, Perez-Puyana V, Romero A, Guerrero A (2017) Development of protein-based bioplastics modified with different additives. J Appl Polym Sci 143:45430. 10.1002/app.45430
McKeen L (2021) The effect of heat aging on the properties of sustainable polymers. Eff Long Term Therm Expo Plast Elastomers 313–332. 10.1016/b978-0-323-85436-8.00001-1
Ferry JD (1980) Viscoelastic properties of polymers; Wiley, ; ISBN 9780471048947
Chang YP, Abd Karim A, Seow CC (2006) Interactive plasticizing-antiplasticizing effects of water and glycerol on the tensile properties of tapioca starch films. Food Hydrocoll 20:1–8. 10.1016/j.foodhyd.2005.02.004
Sanyang ML, Sapuan SM, Jawaid M, Ishak MR, Sahari J (2015) Effect of plasticizer type and concentration on tensile, thermal and barrier properties of biodegradable films based on sugar palm (Arenga pinnata) starch. Polymers (Basel). 7, 1106–1124, doi:10.3390/polym7061106
Félix M, Martín-Alfonso JEE, Romero A, Guerrero A, Felix M, Martin-Alfonso JE, Romero A, Guerrero A (2014) Development of albumen/soy biobased plastic materials processed by injection molding. J Food Eng 125:7–16. 10.1016/j.jfoodeng.2013.10.018
Guillard V, Chevillard A, Gastaldi E, Gontard N, Angellier-Coussy H (2013) Water transport mechanisms in wheat gluten based (nano) composite materials. Eur Polym J 49:1337–1346. 10.1016/j,eurpolymj.2013.02.035
Arakawa CK, DeForest CA (2017) Chapter 19 - Polymer Design and Development. In; Vishwakarma, A., Karp, J.M.B.T.-B. and E. of S.C.N., Eds.; Academic Press: Boston, ; pp. 295–314 ISBN 978-0-12-802734-9
Buchholz FL, Graham AT (1998) Modern superabsorbent polymer technology. In; Wiley-VCH, ; p. 304 ISBN 978-0-471-19411-8

No competing interests reported.

Download PDF

Version 1

posted

You are reading this latest preprint version

Polycaprolactone and acylated soy protein isolate to tune the features of brown seaweed biocomposites

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials and Methods

2.1. Materials

2.2. Methods

2.2.1 Sample Preparation

2.2.2. Rheological Characterization of Composites Blends

2.2.3. Characterization of the Composite Bioplastics

3. Results and discussion

3.1. Blends

3.2. Injection molded biocomposites.

3.3. Tensile tests

3.4. Water Uptake Capacity

3.5. Scanning Electron Microscopy

4. Conclusions

Declarations

References

Additional Declarations

Status:

Version 1