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Reactive extrusion (REX) offers a fast, facile, solvent-free, and cost-effective route towards the adoption of green technologies in the commercial space, thus advancing the cause for sustainable industrial practices. In the following work, we present a brief summary of the use of REX in our group to develop value-added biobased or biodegradable pr...
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... exists as a mixture of two isomers, amylose and amylopectin, in varying ratios depending on its source. As shown in Figure 2, amylose exists as a linear chain of α D-glucose units linked to each other through α(1→4) linkages, whereas amylopectin forms a branched structure with α(1→4) linear linkages and α(1→6) linkages at the branching nodes. The ratio of the amylose to the amylopectin in starch leads to different physical and mechanical properties (10). ...
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... is a naturally occurring anhydroglucose polymer that is typically derived from plant-based biomass. Its use as a biobased platform for the production of polymeric materials has been extensively studied and documented (8,9). Since it is inexpensive, easily available from biobased sources, and also biodegradable, starch makes for an ideal choice of raw material for the development of sustainable commodity plastics. Starch exists as a mixture of two isomers, amylose and amylopectin, in varying ratios depending on its source. As shown in Figure 2, amylose exists as a linear chain of ? D-glucose units linked to each other through ?(1?4) linkages, whereas amylopectin forms a branched structure with ?(1?4) linear linkages and ?(1?6) linkages at the branching nodes. The ratio of the amylose to the amylopectin in starch leads to different physical and mechanical properties (10). Despite its merits, the two major issues that starch poses in terms of being used as a substitute for conventional plastics are its poor melt processability and its hydrophilicity. The first arises from the fact that starch is not a thermoplastic material and hence does not melt, while the latter owes it to the presence of multiple hydroxyl groups on the starch backbone which leads to extensive hydrogen bonding in the presence of water. The issue with melt processing is addressed by the addition of a plasticizer, most commonly water or glycerol, which breaks down the semi-crystalline structure of starch in the presence of elevated temperatures and shear forces in an extruder (11). Thermoplastic starch, the resultant product can then undergo further processing to produce injection molded articles or blown films. The hydrophilicity of starch is usually reduced through its melt-blending with more hydrophobic polymers or reacting it with a dibasic acid or acid anhydride in the presence of a plasticizer (12). REX has been successfully used to carry out extensive chemical modification of starch in order to functionalize it for various applications (13). Our group has expressly worked on the production of starch foams, the maleation and plasticization of starch and its subsequent transesterification with biobased polyesters to make blown ...
Citations
... Reactive extrusion (REX) was not used. REX offers several advantages over traditional batch and flow reactors (CSTR, PFR), such as fast reaction time, enhanced heat and mass transfer, and better mixing, and it does not require any solvents [34]. To the best of our knowledge, there are no reports of using this grafting reaction for PETG. ...
... Lopez et al. (2019) showed that the use of St-g-PCL as a compatibilizer in starch/PCL blends improved the interfacial adhesion between the two polymers, and the maximum tensile strength and tensile modulus were significantly increased compared to the noncompatibilized blends [43]. Similar results were also obtained by Giri (2018), where melt blending of PLA-g-PDMS copolymer with PLA showed significant improvement in tensile properties and toughness of PLA [34]. It would be very interesting to see the impact of MTPS-g-PETG on the properties of MTPS/PETG blends. ...
... Lopez et al. (2019) showed that the use of St-g-PCL as a compatibilizer in starch/PCL blends improved the interfacial adhesion between the two polymers, and the maximum tensile strength and tensile modulus were significantly increased compared to the noncompatibilized blends [43]. Similar results were also obtained by Giri (2018), where melt blending of PLA-g-PDMS copolymer with PLA showed significant improvement in tensile properties and toughness of PLA [34]. It would be very interesting to see the impact of MTPS-g-PETG on the properties of MTPS/PETG blends. ...
This paper reports on synthesis of modified thermoplastic starch (MTPS) and glycol-modified polyethylene terephthalate (PETG) blends in a twin-screw extruder. Scanning electron microscopy (SEM) images showed uniform, microdispersion of MTPS in PETG matrix, confirming compatibilization of the blend by graft copolymers generated in situ during the reactive extrusion process. Incorporating 30% by wt. MTPS in the blend gives a biobased carbon content of 22.8%, resulting in reduced carbon footprint by removal of 0.5 kg CO2 from the environment/kg resin relative to unmodified PETG. MTPS with 80% glycerol grafted onto starch was prepared by reactive extrusion in the twin-screw extruder. A total of 33% of added PETG was grafted on MTPS backbone as determined by soxhlet extraction with dichloromethane (DCM). The grafting was confirmed by presence of PETG peak in the TGA analysis of residue and appearance of carbonyl peak in FTIR spectra of the residue after Soxhlet extraction. The synthesized MTPS–PETG reactive blend had lower but acceptable mechanical properties. Even after a 15% reduction in the tensile stress and 40% reduction in the strain and impact strength obtained after adding 30% MTPS, this blend still had good mechanical properties and can be used in many applications requiring a balance of cost, mechanical properties, and biobased content. Aqueous biodegradability studies using ISO 14852 showed that the 30% starch component in the blend biodegraded rapidly within 80 days, whereas PETG remained as it was even after 150 days. Thus, this study categorically proves that addition of starch does not improve the biodegradability of nonbiodegradable polymers.
... Starch granules consist of concentric alternating amorphous and semi-crystalline polysaccharide molecules packed with amylopectin and amylose [20,21]. In Fig. 3 (a), it can be seen that amylopectin is a highly branched α-D-(1-4)-glucan with α-D-(1-6)-glucan linkages at the branch point, whereas amylose, in Fig. 3 (b), is a linear chain composed of α-D-(1-4)-glucan units [22]. The ratio of amylopectin to amylose depends on the botanical origin and genetic background of each starch, but it usually consists of 70 to 80% of amylopectin and 20 to 25% of amylose [23]. ...
... It can be used directly as native starch or treated starch. However, native starch is unsuitable for specific industrial applications due to several functional limitations, including low solubility, low retrogradation, restricted digestibility, poor thermal stability, and susceptibility to shear stress [22,23,26]. For this reason, starch is usually treated to diversify its structural and functional properties to fit various applications [27]. ...
... However, both methods tend to destroy the crystalline structure of the starch due to the prolonged treatment time and additional energy required [36,37]. Nevertheless, some studies have used ultrasound in combination with chemical modifications, such as [22]. Reproduced with permission from American Chemical Society Content courtesy of Springer Nature, terms of use apply. ...
Nanostarch is unique in that it is highly soluble, thermally stable, non-toxic and inexpensive. Hence, it is utilized in numerous well-established applications, including drug delivery, cosmetics, textiles, foods, and enhanced oil recovery (EOR). These applications take advantage of the special functions that can be achieved through modifications to the structure and properties of native starch. The most common method for the preparation of nanostarch with a relatively higher crystallinity and stability is acid hydrolysis. Technically, the properties of nanostarch are highly dependent on several factors during the hydrolysis process, such as the acid, concentration of acid, reaction time, reaction temperature, and source of starch. The production of nanostarch with desired properties requires a detailed understanding on each of the factors as they are inevitably affected the physical and chemical properties of nanostarch. Hence, it is vital to incorporate optimization technique into the production process to achieve the full potential of nanostarch. Therefore, the current review comprehensively elaborates on the factors that affect acid hydrolysis as well as the optimization techniques used in the preparation of nanostarch.
... The structure of the glycerylated starch polymer is shown below in Figure 1 and described in our earlier papers [23][24][25]. REX offers several advantages over traditional batch and flow reactors (CSTR, PFR) like fast reaction time, enhanced heat and mass transfer, better mixing and does not require any solvents [26]. Starch based films have shown some desirable properties like high barrier to oxygen and CO2 which is useful in packaging [27,28]. ...
... Several strategies have been tried to improve the compatibility by modifying either PLA or starch [29][30][31]. REX offers several advantages over traditional batch and flow reactors (CSTR, PFR) like fast reaction time, enhanced heat and mass transfer, better mixing and does not require any solvents [26]. Starch based films have shown some desirable properties like high barrier to oxygen and CO 2 which is useful in packaging [27,28]. ...
This study reports on using reactive extrusion (REX) modified thermoplastic starch particles as a bio-based and biodegradable nucleating agent to increase the rate of crystallization, percent crystallinity and improve oxygen barrier properties while maintaining the biodegradability of PLA. Reactive blends of maleated thermoplastic starch (MTPS) and PLA were prepared using a ZSK-30 twin-screw extruder; 80% glycerol was grafted on the starch during the preparation of MTPS as determined by soxhlet extraction with acetone. The crystallinity of PLA was found to increase from 7.7% to 28.6% with 5% MTPS. The crystallization temperature of PLA reduced from 113 °C to 103 °C. Avrami analysis of the blends showed that the crystallization rate increased 98-fold and t1/2 was reduced drastically from 20 min to <1 min with the addition of 5% MTPS compared to neat PLA. Observation from POM confirmed that the presence of MTPS in the PLA matrix significantly increased the rate of formation and density of spherulites. Oxygen and water vapor permeabilities of the solvent-casted PLA/MTPS films were reduced by 33 and 19% respectively over neat PLA without causing any detrimental impacts on the mechanical properties (α = 0.05). The addition of MTPS to PLA did not impact the biodegradation of PLA in an aqueous environment.
... Recently, reactive extrusion (REX) is being used to overcome the aforementioned drawbacks, considering that functional molecules are anchored into the polymeric matrix. REX technology provides stable and irreversible covalent bonds, achieving a uniform distribution of functional moieties into the polymer matrix and avoiding particle aggregation, migration, and leaching [24][25][26]. Furthermore, reactive extrusion offers a one-step solvent-free route to produce novel and high-performance materials with new functionalities [27]. ...
An eco-friendly strategy for the modification of polylactic acid (PLA) surface properties, using a solvent-free process, is reported. Reactive extrusion (REX) allowed the formation of new covalent bonds between functional molecules and the PLA polymeric matrix, enhancing its mechanical properties and modifying surface hydrophobicity. To this end, the PLA backbone was modified using two alkoxysilanes, phenyltriethoxysilane and N-octyltriethoxysilane. The reactive extrusion process was carried out under mild conditions, using melting temperatures between 150 and 180 °C, 300 rpm as screw speed, and a feeding rate of 3 kg·h−1. To complete the study, flat tapes of neat and functionalized PLA were obtained through monofilament melt extrusion to quantify the enhancement of mechanical properties and hydrophobicity. The results verified that PLA modified with 3 wt% of N-octyltriethoxysilane improves mechanical and thermal properties, reaching Young’s modulus values of 4.8 GPa, and PLA hydrophobic behavior, with values of water contact angle shifting from 68.6° to 82.2°.
Polysaccharides are high molecular weight biopolymers composed of repeated monosaccharide units linked via glycosidic bonds. They are the most abundant biopolymers in nature synthesized via the process of photosynthesis using inorganic carbon source (CO2) and water. Polysaccharides provide both structural and food reserve (energy) values. The natural polysaccharides demonstrate diverse physiological functions that arise due to various structural characteristics. For instance, the inter‐linkages (glycosidic) between monosaccharides chains in a biopolymer, like cellulose, is strong enough to enhance immiscibility with water. On the contrary, monosaccharides of the polysaccharide called starch are linked in a unique fashion to make starch water‐soluble and digestible. Polysaccharides are mostly non‐toxic and hence have been employed for various food, biomedical, and pharmaceutical applications. These applications rely on the solubility of polysaccharides in suitable solvents (e.g. water). This chapter will discuss the interactions occurring between water and polysaccharide molecules as well as the monomer linkages present in it, which influence the polysaccharide dissolution in water.
