Introduction
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Polymer-based plastic materials accumulate in marine environments (Great Pacific Garbage Patch), (1) land, (2) and as microplastics, in drinking water, (3) and air, (4) resulting in acute environmental and health problems. (5) This is because most plastics are not biodegradable, often being discarded as waste, while recycled plastic constitutes only 9–18% of the plastic matter ever produced. (2,5) There is an ongoing effort to develop biodegradable plastics, but the limited range of available materials and their properties hinder wide utilization. (6)
Material strength and ductility (plastic strain) are usually mutually exclusive mechanical properties. One of the key challenges in materials science is to resolve the conflict of simultaneously attaining strength and ductility. (7,8) Biological materials often demonstrate high strength and ductility, owing to advantageous arrangement of rigid and soft components. (9−12) A prime example of outstanding mechanical properties is represented by silk where intricate arrangement of rigid crystalline and softer amorphous protein regions results in a superbly strong material that is entirely organic; (11) however, emulating these attributes in artificial materials has proven to be extremely challenging.
Some crystalline organic materials based on biomolecules exhibit high Young’s moduli. (13) We envisaged that interfacing such biomolecular crystals with biodegradable polymers could lead to biodegradable materials with superior mechanical properties. In this respect, organic crystals offer distinct advantages: they may have high affinity to the polymer matrix and, in the case of nanocrystals, allow nanostructured morphology advantageous to mechanical properties. Importantly, the organic nanocrystals based on small molecules can be grown directly within the polymer matrix, unlike conventional rigid fillers. Furthermore, biomolecular crystal/polymer self-assembly can be performed in aqueous media, thus enabling sustainable fabrication and advantageous assembly modes. (14,15)
Herein, we report on the fabrication of a biodegradable composite material based on a hydroxyethyl cellulose (HEC) polymer and tyrosine (Tyr) nanocrystals (Figure 1). This material demonstrates enhancement in modulus, strength, and ductility (strain), superior to most biodegradable plastics. The emergent behavior is achieved by a specific assembly pattern, resulting in strong Tyr/HEC interactions and a distinctive nanoscale morphology. Self-assembly of robust sustainable plastics with emergent properties using readily available building blocks provides a valuable toolbox for creating sustainable materials.
Figure 1
Figure 1. Molecular structure of Tyr and HEC.
Results and Discussion
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Our material design concept was based on the idea that linear, flexible polysaccharide chains may interact favorably with Tyr crystals that exhibit high Young’s modulus (20–40 GPa (16)), especially if these crystals were grown within the polymer matrix. The ductile polysaccharide combined with the stiff Tyr crystals could effectively result in reinforcement of the composite structure. We chose alginate, agarose, and hydroxyethyl cellulose (HEC) as polymer matrices, based on their high ductility, solubility in aqueous medium, cost, availability, biodegradability, and biocompatibility. We observed no enhancement in mechanical properties when using alginate, a modest improvement with agarose (Figure S1), and a substantial enhancement with HEC (as discussed below).
To fabricate a hybrid material, we interfaced Tyr nanocrystals with an HEC polymer (Figure 1). HEC, a ductile linear polymer obtained by chemical modification of native cellulose, serves as a gelling and thickening agent, widely used in personal care products, coatings, pharmaceuticals, and adhesives. (17) The fabrication of the HEC/Tyr composite was carried out in aqueous solution (see the Experimental Section). Briefly, Tyr dissolved in boiling water was added to an aqueous solution of HEC, and the resulting mixture was stirred at ambient temperature, becoming opaque after several hours due to Tyr crystallization. The mixture was cast onto either a Petri dish or a rectangular mold to afford solid semitransparent films, 20–50 μm in thickness, after drying overnight at ambient conditions (Figure 2a). Optical microscopy and SEM images (Figure 2) of the resultant HEC/Tyr films showed a uniform distribution of the Tyr crystals within the polymer matrix. The films retained 8–10% water by weight, as indicated by TGA (Figure S2), with this content remaining constant at ambient conditions for months. The presence of Tyr crystals in the composite was confirmed by XRD (Figure 3) and Raman spectroscopy (Figure S3), indicating that the crystals correspond to a known crystal structure of Tyr. (16) XRD indicates that the Tyr crystals exhibit similar orientation as expected for needle-like crystals, which commonly exhibit parallel alignment with the substrate they are deposited onto. TGA, DSC, and XRD revealed that the films retain their structure up to 150 °C, except for the water loss (Figures S2, S4, S5).
Figure 2
Figure 2. HEC/Tyr (10:3, wt %) film. (a) A photograph of the film. (a–c) SEM images: (b) top view; (c) cross section; (d) zoomed-in image of the cross section.
Figure 3
Figure 3. XRD diffractograms of Tyr crystals, HEC, and HEC/Tyr hybrids.
HEC/Tyr composites exhibit a significant increase in modulus, strength, and elongation in comparison to pure HEC (Figure 4a, Table 1). For example, the HEC/Tyr composite with a composition of 10:3 wt % exhibited a 3-fold increase in modulus and 40% increase in strain (Figure 4a, Table 1), resulting in a 6-fold rise in toughness. Above 40 wt % Tyr, the HEC/Tyr mechanical properties deteriorated (Table 1, HEC:Tyr = 10:5 wt %) due to defects resulting from the high Tyr loading (Figure S6). To further exemplify the robustness of the composite, we conducted a weight-bearing test using 40-μm thick composite strips. These strips exhibited stability under a load of 6 kg without any noticeable deformation, underscoring the load-bearing capacity of the material (Figure 4b).
Table 1. Mechanical Properties of HEC and HEC/Tyr Hybrids
Figure 4
Figure 4. (a) Representative stress–strain curves of HEC (red) and HEC/Tyr hybrids: 10:2 (w/w, blue), 10:3 (w/w, black), 10:4 (w/w, green); (b) HEC/Tyr (10/3, w/w) hybrid stripe, 40-μm thick, lifting 6-kg weight.
In terms of enhanced strength and toughness, Tyr/HEC outperforms biodegradable or partially biodegradable plastics used for packaging, such as starch blends (including thermoplastic starch, TPS), (18) Polylactic acid (PLA), (19,20) Polyglycolic acid (PGA), (21) PLA/PGA blends, (21,22) TPS blends based on low density polyethylene (LDPE), (19,23) PLA blends with high density polyethylene, (24) and several other materials (Table S1). While stable at ambient humidity, HEC/Tyr slowly absorbs liquid water, giving rise to a gel-like material. In order to create a water-resistant material, HEC/Tyr was laminated with polycaprolactone (PCL), a soft synthetic biodegradable polymer. (25) The resultant material showed mechanical properties comparable to those of the parent HEC/Tyr (Table S2), and resistance to water (Figures S7 and S8, and Table S3).
HEC/Tyr and HEC/Tyr/PCL showed good biodegradability under standard conditions using the CO2 evolution test (see Experimental Section for details), losing 33 and 52 wt % respectively within 149 days (Figure 5). Further studies are planned in order to assess longer-term degradation of the systems.
Figure 5
Figure 5. Biodegradation of the plastics.
The emergent mechanical properties of the Tyr/HEC arise from the specific assembly pattern resulting from the Tyr crystal growth within the HEC matrix. Thus, mixing the preformed Tyr nanocrystals with the HEC solution and subsequent drying resulted in an inhomogeneous material that had unsatisfactory mechanical properties.
In order to obtain an insight into the assembly of the material, we performed SEM and cryo-SEM follow-up of the crystal growth within the polymer matrix (Figures 6 and S9–S13). While Tyr crystallizes into needle-like crystals from water, its crystallization within HEC solution gives rise to dendritic structures. Initially, thin needle-like Tyr crystallites form bundles that develop a fractal morphology (Figures 6a and S9). Subsequently, the crystals continue to grow, giving rise to larger stem-like bundles with branching structures (Figures 6b–d and S10, S11). Over time, this complex morphology evolves into a branched crystalline fibril network embedded within the HEC matrix (Figures 6f and S12, S13). The cryo-SEM image of the material at the end of the fabrication process revealed that the polymer chains envelop the uniformly dispersed Tyr nanocrystalline bundles, resulting in the interpenetrating HEC/Tyr network (Figures 6e,f and S13). Overall, Tyr crystal growth within the HEC polymer results in a branched network entrapped within polymer chains as a result of confinement imposed by the polymer matrix. The uniformity of the fibrillary network and its advantageous interaction pattern with HEC led to the synergy in terms of the mechanical properties: Young’s modulus increases owing to the rigid nature of the Tyr crystals, and the strain grows due the interpenetrating network, where the crystals contribute to the “unwinding” of HEC chains. (6) Strong HEC/Tyr interactions were revealed by SEM imaging of the film cross sections following the tensile failure. It showed a sharp rupture pattern, featuring a uniform edge that indicates concurrent HEC and Tyr breakage, but also a slippage of the crystalline layers against each other, and the occasional protruding crystals, implying a pull-out mechanism accounting for high strain that leads to the tough material (Figure S14).
Figure 6
Figure 6. SEM (a–c) and cryo-SEM images (d–f) of Tyr crystal growth within aqueous HEC solution following addition of Tyr dissolved in hot water (final composition: HEC:Tyr = 10:3). (a) Immediately after mixing; (b) 30 min after mixing; (c) 1 h; (d) 90 min; (e–f) mature hybrid before water evaporation.
Evidently, wrapping of the HEC chains around the Tyr crystals (Figures 6f and S13) imposes significant mechanical interactions due to intimate polymer/crystal entanglement. These may be further augmented by noncovalent interactions, for example hydrogen bonding between the polymer chains and crystals. The latter could not be directly elucidated by Raman spectroscopy (Figure S3) due to multiple overlapping peaks, yet it is plausible based on the interaction mode observed in SEM (Figure 4). We further note that growing the Tyr crystals within the HEC matrix leads to the system where the crystalline and polymer networks must accommodate each other, as evidenced by the uniform Tyr crystal embedding pattern (Figures 6f and S13).
Strength/ductility trade-off precludes parallel increase of both. Typically, in polymer-based composites, reinforcing polymers with strong and stiff fillers such as glass and carbon fibers, clays, and nanocrystalline cellulose (NCC) yields composites with enhanced strength, but with lower strain (related to ductility) and toughness due to defect formation and other factors. (26) Enhancing both strength and ductility can be achieved via precise control over the nanoscale structure, components distribution, and interaction patterns, as realized in biological materials such as bone, nacre, and silk. (9−12) Tyr crystal growth within a polymer matrix allows optimal interactions, minimizing the defects and eventually forming a crystal network superbly entangled with the polymer matrix. The larger crystalline bundles that branch fibrous crystals represent additional cross-links within the system.
Conclusions
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We present a useful paradigm for sustainable plastic materials, employing a soft polymer matrix with biomolecular crystals grown within it, giving rise to both strong and ductile biodegradable plastic materials. Growing crystals within a polymer matrix affords an advantageous structure: the uniform crystalline network interwoven with the polymer one, leading to emergent mechanical properties represented by increase in modulus, strength, and strain. Water-resistant composites, Tyr/HEC encapsulated with hydrophobic PCL as a protection layer, were also fabricated, retaining biodegradability and enhanced mechanical performance. Emergent self-assembly of biodegradable plastic materials from readily available biomolecular building blocks was enabled by a simple crystallization process in an aqueous medium, conceptually advancing the development of sustainable plastics.
Experimental Section
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Solvents and reagents were purchased from commercial sources and used as received unless otherwise indicated. For all aqueous mixtures, double-distilled water (DDW) was used (Barnstead NANOpure Diamond water system). Organic solvents for spectroscopic and microscopic studies were of HPLC grade.
Sodium alginate (viscosity of 2% solution ∼250 cps, A2158), agarose (low gelling temp. BioReagent, A9414), HEC (2-hydroxyethyl cellulose, Mw = 1 × 106 g·mol–1), l-Tyrosine, and Polycaprolactone (Mw = 8.4 × 104 g·mol–1) were purchased from Sigma-Aldrich.
Scanning electron microscopy (SEM) imaging was performed using a Zeiss Supra 55 FEG-SEM or Ziess Ultra 55 FEG-SEM operating at 1–20 kV. Images were obtained using a working distance (WD) of 3–5 mm and a standard aperture (30 μm).
Cryo-SEM sample preparation involved a high-pressure freezing (HPF) technique. The samples were cut using a razor blade to fit in an aluminum disc (outer diameter 3.0 mm, thickness 0.5 mm, inner diameter 2.0 mm, depth 0.2 mm). 1-Hexadecane was used for filling empty space, and the disc was sealed with a flat disc. HPF was carried out using a Bal-Tec HPM 010. Subsequently, the frozen sample was transferred into a BAF 060 (Leica Microsystems, Vienna, Austria) freeze fracture system where it was fractured with a precooled razor blade. Solvent was allowed to sublime (−80 °C, 30 min). The sample was then transferred to an Ultra 55 cryo-SEM (Zeiss) using the VCT 100 cryo-transfer holder and was imaged at an acceleration voltage of 1–3 kV using the in-lens detector.
Tensile tests
For the tensile test experiments, all samples were cut into thin strips of 2–3 mm in width, thickness of 30–50 μm, and length of ∼20 mm and measured with an Instron Model 5965 Materials Testing System, equipped with a 50 kN load cell. The deformation rate was 0.2 mm/min. At least 10 specimens of each type were tested. The dimensions of the film were measured using caliber and micrometer.
Bath Sonication was performed using MRC Ultrasonic Cleaner D80H. Operation frequency was 43 kHz, and power 80 W.
Thermogravimetric Analysis (TGA) experiments were conducted using the thermal analyzer SDT Q 600 (TA Instruments), under air flow (100 mL/min) with a heating rate of 20 °C/min. Samples were measured in alumina pans.
Differential Scanning Calorimetry (DSC)
Experiments were conducted using a DSC Q200 (TA Instruments), under a N2 flow (1 mL/min) with a heating rate of 10 °C/min. Samples were measured in aluminum T-Zero pans.
Powder X-ray Diffraction (pXRD)
Temperature controlled measurements were made in an Ultima III theta–theta diffractometer (Rigaku, Japan) equipped with a sealed copper anode X-ray tube operating at 40 kV and 40 mA. A bent graphite monochromator and a scintillation detector were aligned in the diffracted beam. θ/2θ scans were performed under specular conditions in Bragg–Brentano geometry with variable slits. The test sample was placed in a medium/low temperature attachment (Rigaku), and its temperature was controlled by a PTC-30 programmable temperature controller. Phase analysis was performed using the Jade Pro software (MDI, icdd.com).
Raman Spectroscopy
Raman scattering measurements were performed in backscattering mode using a LabRAM HR Evolution (Horiba, France) confocal microspectrometer using 532 nm excitation. The maximum incident power on the sample was 1–2 mW with a submicrometer spot size. The Raman spectra were collected by a 1024 × 256 pixel open electrode front-illuminated CCD camera (Syncerity, Horiba, x ur home, USA) cooled to −60 °C. The spectra were baseline corrected.
Preparation of Tyr nanocrystals
Tyr (20 mg) was dissolved in boiling DDW (20 mL) for 30 min until the solution was clear, and the solution was filtered through a poly(ether sulfone) (PES) syringe filter (0.22 μm). The filtered solution was sonicated in a bath sonicator for 3 min, until turbidity was observed. The vial was placed under ambient conditions to allow the precipitation of fibrous Tyr crystals.
Preparation of composites
Tyr/HEC. Hydroxyethyl cellulose (100 kDa, 100 mg) was dissolved in 6 mL of water and stirred for 48 h.
Tyr (20–50 mg) was dissolved in boiling DDW (14 mL) until the solution was clear, and then the solution was filtered through a poly(ether sulfone) (PES) syringe filter (0.22 μm).
The hot Tyr solution was added to the HEC solution, and the mixture was stirred at rt for 12 h to allow the crystallization of Tyr. The mature hybrid was either air-dried in molds having a rectangular (20 cm × 10 cm) or circular (diameter of 10 cm) shape. The resulting film was manually detached.
Neat HEC film preparation. A dispersion of HEC (100 mg in 20 mL of water) was placed in a form and then dried in ambient conditions to yield a film of neat HEC
PCL/HEC/Tyr. Tyr/HEC hybrid films were placed between two PCL films (50 mg each) in a sandwich-like configuration; the triple composite was sealed by heat-press at 80 °C to yield a PCL/HEC/Tyr hybrid film with the HEC/Tyr encapsulated between the PCL layers.
Neat PCL film preparation. PCL (50 mg) was dissolved in CHCl3, and after PCL was fully dissolved, Dimethylformamide (DMF) was added to the solution. The solvents were slowly evaporated on a hot plate (100 °C) using a custom-designed Teflon plate. After solvent evaporation, the PCL film was manually detached from the support.
Biodegradability test
Biodegradability was evaluated according to the standard ISO 17556 procedure at IMI TAMI Institute for Research & Development Ltd., Haifa Bay 2611101, Israel. The samples (films) were ground in a cariogenic mill to result in 300–600 μm particles. The test involved 1.25 g of the polymers (each experiment was duplicated) in the 2 L bioreactors that contained 200 g of inoculum concentrate + vermiculite, activated for a week at 28 ± 1 °C. Vessels with NaOH solution were used for CO2 adsorption. Samples for determination of the CO2 content were taken on a weekly basis. The test was performed for 149 days. The blank treatments (duplicates, no biodegrading medium) produced an amount of ∼20% CO2 compared to the samples in the inoculum, as required in ISO 17556.
Supporting Information
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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsnano.3c02528.
TGA, Raman, DSC, XRD data. Agarose/Tyr data. PCL/HEC/Tyr composite data. Additional SEM images. (PDF)
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Author Information
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Angelica Niazov-Elkan - Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel
Haim Weissman - Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel
Eyal Shimoni - Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
XiaoMeng Sui - Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel; Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
Yishay Feldman - Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
H. Daniel Wagner - Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel
The authors declare no competing financial interest.
Acknowledgments
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This research was supported by grants from Minerva Foundation, Israel Science Foundation, and The Helen and Martin Kimmel Center for Molecular Design. The support of the EM imaging by the Irving and Cherna Moskowitz Center for Nano and Bio-Nano Imaging is gratefully acknowledged. This research was also supported in part by the generosity of the Harold Perlman family. H.D.W. is the recipient of the Livio Norzi Professorial Chair in Materials Science. We thank Iddo Pinkas (Weizmann Institute) for performing the Raman spectroscopy measurements, and Dorit Abramovich (IMI TAMI) for performing the biodegradability experiments.
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Bioplastics - typically plastics manufactured from bio-based polymers - stand to contribute to more sustainable commercial plastic life cycles as part of a circular economy, in which virgin polymers are made from renewable or recycled raw materials. Carbon-neutral energy is used for production and products are reused or recycled at their end of life (EOL). In this Review, we assess the advantages and challenges of bioplastics in transitioning towards a circular economy. Compared with fossil-based plastics, bio-based plastics can have a lower carbon footprint and exhibit advantageous materials properties; moreover, they can be compatible with existing recycling streams and some offer biodegradation as an EOL scenario if performed in controlled or predictable environments. However, these benefits can have trade-offs, including negative agricultural impacts, competition with food production, unclear EOL management and higher costs. Emerging chemical and biological methods can enable the 'upcycling' of increasing volumes of heterogeneous plastic and bioplastic waste into higher-quality materials. To guide converters and consumers in their purchasing choices, existing (bio)plastic identification standards and life cycle assessment guidelines need revision and homogenization. Furthermore, clear regulation and financial incentives remain essential to scale from niche polymers to large-scale bioplastic market applications with truly sustainable impact.
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A review. Metals can be processed to reach ultra-high strength, but usually at a drastic loss of ductility. Here, we review recent advances in overcoming this tradeoff, by purposely deploying heterogeneous nanostructures in an otherwise single-phase metal. Several structural designs are being explored, including bimodal, harmonic, lamellar, gradient, domain-dispersed, and hierarchical nanostructures. These seemingly distinct tactics share a unifying design principle in that the intentional structural heterogeneities induce non-homogeneous plastic deformation, and the nanometer-scale features dictate steep strain gradients, thereby enhancing strain hardening and consequently uniform tensile ductility at high flow stresses. Moreover, these heterogeneous nanostructures in metals play a role similar to multiple phases in complex alloys, functionally graded materials and composites, sharing common material design and mechanics principles. Our review advocates this broad vision to help guide future innovations towards a synergy between high strength and high ductility, through highlighting several recent designs as well as identifying outstanding challenges and opportunities.
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Iptycenes in the Design of High Performance Polymers
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A review. This Account reviews the use of building blocks known as iptycene units, which are particularly useful in the design of advanced materials because of their three-dimensional, noncompliant structures. Iptycenes are built upon [2,2,2]-ring systems in which the bridges are arom. rings, and the simplest member of this class of compds. is triptycene. Iptycenes can provide steric blocking, which can prevent strong interactions between polymeric chromophores that have a strong tendency to form nonemissive exciplex complexes. Iptycene-contg. conjugated polymers are exceptionally stable and display soln.-like emissive spectra and quantum yields in the solid state. This application of iptycenes has enabled new vapor detection methods for ultratrace detection of high explosives that are now used by the U.S. military. The three-dimensional shape of iptycenes creates interstitial space (free vol.) around the mols. This space can confer size selectivity in sensory responses and also promotes alignment in oriented polymers and liq. crystals. Specifically, the iptycene-contg. polymers and mols. align in the anisotropic host material in a way that minimizes the free vol. This effect can be used to align mols. contrary to what would be predicted by conventional models on the basis of aspect ratios. In one demonstration, we show that an iptycene polymer aligns orthogonally to the host polymer when stretched, and these structures approx. mol. versions of woven cloth. In liq. crystal solns., the conjugated iptycene-contg. polymers exhibit greater electronic delocalization, and the transport of excited states along the polymer backbone is obsd. Structures that preserve high degrees of internal free vol. can also be designed to create low dielec. const. insulators. These materials have high temp. stability (>500 °C) and hardness that make them potential interlayer dielec. materials for integrated circuits. In cases where the iptycene structures are less densely spaced along the polymer backbones, interlocking structures can be created. These structures allow for small interpolymer motions, but at large deformations, the steric clashes between iptycenes result in the transfer of load from one polymer to another. This mechanism has the ability to impart greater modulus, strength, and ductility. It is difficult to increase modulus without adversely affecting ductility, and classical high-modulus materials have low ductility. As a result, the use of interlocking iptycene structures is a promising approach to new generations of structural materials.
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Bar-On Benny; Wagner H Daniel
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Biological tissues usually exhibit complex multiscale structural architectures. In many of these, and particularly in mineralized tissues, the basic building block is a staggered array-a composite material made of soft matrix and stiff reinforcing elements. Here we study the stiffness of non-overlapping staggered arrays, a case that has not previously been considered in the literature, and introduce closed-form analytical expressions for its Young's modulus. These expressions are then used to estimate the stiffness of natural staggered biocomposites such as low-mineralized collagen fibril and mineralized tendon. We then consider a two-scale composite scheme for evaluating the modulus of a specific hierarchical structure, the compact bone tissue, which is made of mineralized collagen fibrils with weakly overlapping staggered architecture. It is found that small variations in the staggered structure induce significant differences in the macroscopic stiffness, and, in particular, provide a possible explanation for the as yet unexplained stiffening effects observed in medium-mineralized tissues.
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Bouhlel, Z.; Genard, B.; Ibrahim, N.; Carrington, E.; Babarro, J. M. F.; Lok, A.; Flores, A. A. V.; Pellerin, C.; Tremblay, R.; Marcotte, I. Interspecies comparison of the mechanical properties and biochemical composition of byssal threads. J. Exp. Biol. 2017, 220 (6), 984– 994
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Interspecies comparison of the mechanical properties and biochemical composition of byssal threads
Bouhlel Zeineb; Tremblay Rejean; Genard Bertrand; Marcotte Isabelle; Ibrahim Neilly; Pellerin Christian; Carrington Emily; Babarro Jose M F; Lok Aynur; Flores Augusto A V
The Journal of experimental biology (2017), 220 (Pt 6), 984-994 ISSN:.
Several bivalve species produce byssus threads to provide attachment to substrates, with mechanical properties highly variable among species. Here, we examined the distal section of byssal threads produced by a range of bivalve species (Mytilus edulis, Mytilus trossulus, Mytilus galloprovincialis, Mytilus californianus, Pinna nobilis, Perna perna, Xenostrobus securis, Brachidontes solisianus and Isognomon bicolor) collected from different nearshore environments. Morphological and mechanical properties were measured, and biochemical analyses were performed. Multivariate redundancy analyses on mechanical properties revealed that byssal threads of M. californianus, M. galloprovincialis and P. nobilis have very distinct mechanical behaviours compared with the remaining species. Extensibility, strength and force were the main variables separating these species groups, which were highest for M. californianus and lowest for P. nobilis Furthermore, the analysis of the amino acid composition revealed that I. bicolor and P. nobilis threads are significantly different from the other species, suggesting a different underlying structural strategy. Determination of metal contents showed that the individual concentration of inorganic elements varies, but that the dominant elements are conserved between species. Altogether, this bivalve species comparison suggests some molecular bases for the biomechanical characteristics of byssal fibres that may reflect phylogenetic limitations.
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Hu, X.; Cebe, P.; Weiss, A. S.; Omenetto, F.; Kaplan, D. L. Protein-based composite materials. Mater. Today 2012, 15 (5), 208– 215, DOI: 10.1016/S1369-7021(12)70091-3
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Protein-based composite materials
Hu, Xiao; Cebe, Peggy; Weiss, Anthony S.; Omenetto, Fiorenzo; Kaplan, David L.
Materials Today (Oxford, United Kingdom) (2012), 15 (5), 208-215CODEN: MTOUAN; ISSN:1369-7021. (Elsevier Ltd.)
A review. Protein-based composite biomaterials have been actively pursued as they can encompass a range of phys. properties to accommodate a broader spectrum of functional requirements, such as elasticity to support diverse tissues. By optimizing mol. interfaces between structural proteins, useful composite materials can be fabricated as films, gels, particles, and fibers, as well as for elec. and optical devices. Such systems provide analogies to more traditional synthetic polymers yet with expanded utility due to the material's tunability, mech. properties, degradability, biocompatibility, and functionalization, such as for drug delivery, biosensors, and tissue regeneration.
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Eder, M.; Amini, S.; Fratzl, P. Biological composites-complex structures for functional diversity. Science 2018, 362 (6414), 543, DOI: 10.1126/science.aat8297
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Biological composites - complex structures for functional diversity
Eder, Michaela; Amini, Shahrouz; Fratzl, Peter
Science (Washington, DC, United States) (2018), 362 (6414), 543-547CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
A review. The bulk of Earth's biol. materials consist of few base substances - essentially proteins, polysaccharides, and minerals - that assemble into large varieties of structures. Multifunctionality arises naturally from this structural complexity: An example is the combination of rigidity and flexibility in protein-based teeth of the squid sucker ring. Other examples are time-delayed actuation in plant seed pods triggered by environmental signals, such as fire and water, and surface nanostructures that combine light manipulation with mech. protection or water repellency. Bioinspired engineering transfers some of these structural principles into tech. more relevant base materials to obtain new, often unexpected combinations of material properties. Less appreciated is the huge potential of using bioinspired structural complexity to avoid unnecessary chem. diversity, enabling easier recycling and, thus, a more sustainable materials economy.
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Karothu, D. P.; Halabi, J. M.; Ahmed, E.; Ferreira, R.; Spackman, P. R.; Spackman, M. A.; Naumov, P. Global Analysis of the Mechanical Properties of Organic Crystals. Angew. Chem., Int. Ed. 2022, 61 (10), e202113988, DOI: 10.1002/anie.202113988
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Global Analysis of the Mechanical Properties of Organic Crystals
Karothu, Durga Prasad; Mahmoud Halabi, Jad; Ahmed, Ejaz; Ferreira, Rodrigo; Spackman, Peter R.; Spackman, Mark A.; Naumov, Pance
Angewandte Chemie, International Edition (2022), 61 (10), e202113988CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review. Org. crystals, although widely studied, were not considered nascent candidate materials in engineering design. The mech. properties of org. crystals that were reported over the past 3 decades are summarized, and a global mech. property profile that can be used to predict and identify mech. robust org. crystals is established. Being composed of light elements, org. crystals populate a narrow region in the mech. property-d. space between soft, disordered org. materials and stiff, ordered materials. Two subsets of extraordinarily stiff and hard org. cryst. materials were identified and rationalized by the normalized no. d., strength, and directionality of their intermol. interactions. Future light wt., soft, all-org. components in devices should capitalize on the greatest asset of org. single crystals-namely, the combination of long-range structural order and softness.
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Wang, Q.; Mynar, J. L.; Yoshida, M.; Lee, E.; Lee, M.; Okuro, K.; Kinbara, K.; Aida, T. High-water-content mouldable hydrogels by mixing clay and a dendritic molecular binder. Nature 2010, 463 (7279), 339– 343, DOI: 10.1038/nature08693
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High-water-content moldable hydrogels by mixing clay and a dendritic molecular binder
Wang, Qigang; Mynar, Justin L.; Yoshida, Masaru; Lee, Eunji; Lee, Myongsoo; Okuro, Kou; Kinbara, Kazushi; Aida, Takuzo
Nature (London, United Kingdom) (2010), 463 (7279), 339-343CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
With the world's focus on reducing our dependency on fossil-fuel energy, the scientific community can study new plastic materials that are much less dependent on petroleum than are conventional plastics. Given increasing environmental issues, the idea of replacing plastics with water-based gels, so-called hydrogels, seems reasonable. Here we report that water and clay (2-3% by mass), when mixed with a small proportion (<0.4% by mass) of org. components, quickly form a transparent hydrogel. This material can be molded into shape-persistent, free-standing objects owing to its exceptionally great mech. strength, and rapidly and completely self-heals when damaged. Furthermore, it preserves biol. active proteins for catalysis. So far no other hydrogels, including conventional ones formed by mixing polymeric cations and anions or polysaccharides and borax, were reported to possess all these features. Notably, this material is formed only by non-covalent forces resulting from the specific design of a telechelic dendritic macromol. with multiple adhesive termini for binding to clay.
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Krieg, E.; Bastings, M. M. C.; Besenius, P.; Rybtchinski, B. Supramolecular Polymers in Aqueous Media. Chem. Rev. 2016, 116 (4), 2414– 2477, DOI: 10.1021/acs.chemrev.5b00369
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Supramolecular Polymers in Aqueous Media
Krieg, Elisha; Bastings, Maartje M. C.; Besenius, Pol; Rybtchinski, Boris
Chemical Reviews (Washington, DC, United States) (2016), 116 (4), 2414-2477CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
This review discusses one-dimensional supramol. polymers that form in aq. media. First, naturally occurring supramol. polymers are described, in particular, amyloid fibrils, actin filaments, and microtubules. Their structural, thermodn., kinetic, and nanomech. properties are highlighted, as well as their importance for the advancement of biol. inspired supramol. polymer materials. Second, five classes of synthetic supramol. polymers are described: systems based on (1) hydrogen-bond motifs, (2) large π-conjugated surfaces, (3) host-guest interactions, (4) peptides, and (5) DNA. We focus on recent studies that address key challenges in the field, providing mechanistic understanding, rational polymer design, important functionality, robustness, or unusual thermodn. and kinetic properties.
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Adhikari, R. Y.; Pujols, J. J. Highly rigid & transparent supramolecular fibrils of tyrosine. Nano Select 2022, 3 (9), 1314– 1320, DOI: 10.1002/nano.202200063
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Highly rigid & transparent supramolecular fibrils of tyrosine
Adhikari, Ramesh Y.; Pujols, Jeiko J.
Nano Select (2022), 3 (9), 1314-1320CODEN: NSAECD; ISSN:2688-4011. (Wiley-VCH Verlag GmbH & Co. KGaA)
Various peptides and amino acids can self-assemble into fibrils in a soln. environment both in vivo and in vitro. These fibrils can aggregate as amyloids in the organs of individuals with certain genetic mutations, and can also be assembled in-vitro for their potential application as bioinspired and biocompatible material. Here, we present our study of the mech. properties of self-assembled fibrils of enantiomers of tyrosine, one of the essential amino acids found in living systems. We have obsd. that Young's modulus of fibrils of L-tyrosine, the biol. relevant enantiomer, can be as high as 43 GPa with a point stiffness of about 454 N m-1 making these fibrils to be one of the highly rigid bioinspired structures. We have also obsd. that films of highly rigid L-tyrosine fibrils also have high optical transmittance of 65% while films of enantiomer D-tyrosine fibrils and fibrils of an equimolar mixt. of D- and L-tyrosine are opaque. This suggests that individual amino acids can self-assemble into highly rigid fibrils and opens up avenues for using amino acids for constructing mech. robust structures with varying optical properties.
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Majewicz, T. G.; Podlas, T. J. Cellulose Ethers. In Kirk Othmer Encyclopedia of Chemical Technology, 5th ed.; John Wiley & Sons, Inc.: 2000; Vol. 5, pp 445– 466.
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Cheng, H.; Chen, L.; McClements, D. J.; Yang, T. Y.; Zhang, Z. P.; Ren, F.; Miao, M.; Tian, Y. Q.; Jin, Z. Y. Starch-based biodegradable packaging materials: A review of their preparation, characterization and diverse applications in the food industry. Trends in Food Science & Technology 2021, 114, 70– 82, DOI: 10.1016/j.tifs.2021.05.017
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Starch-based biodegradable packaging materials: A review of their preparation, characterization and diverse applications in the food industry
Cheng, Hao; Chen, Long; McClements, David Julian; Yang, Tianyi; Zhang, Zipei; Ren, Fei; Miao, Ming; Tian, Yaoqi; Jin, Zhengyu
Trends in Food Science & Technology (2021), 114 (), 70-82CODEN: TFTEEH; ISSN:0924-2244. (Elsevier Ltd.)
A review. Synthetic plastics are extremely versatile and convenient materials that can be used to create a diversity of useful products, but their widespread use is causing increasing damage to the planet. As a result, there has been considerable efforts towards the development of more biodegradable and environmentally-friendly materials. Among various alternatives, starch is considered as a good substitute for synthetic polymers due to its abundant supply, low cost, complete biodegrdn., high biocompatibility, and good film-forming properties. However, a no. of tech. challenges need to be overcome to increase the practical of starch-based materials for manner applications. An up-to-date review of starch-based materials is given, with emphasis on methods to improve their properties and widen their application in food packaging. The prepn. methods, common additives, characterization techniques, and applications of starch-based biodegradable materials are summarized. Addnl., advanced technol. approaches to prep. innovative starch-based biodegradable materials are also introduced to stimulate new areas for future research. Starch-based materials have great potential as biodegradable food packaging materials that will reduce environmental pollution. The functional performance of starch-based biodegradable materials can be extended or improved by adding other biopolymers or additives, as well as by using novel prepn. techniques. Nevertheless, the large-scale economic prodn. of high-performance starch-based biodegradable materials is still a challenge and more research is still required in this area.
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Mangaraj, S.; Yadav, A.; Bal, L. M.; Dash, S. K.; Mahanti, N. K. Application of Biodegradable Polymers in Food Packaging Industry: A Comprehensive Review. J. Packaging Technol. Res. 2019, 3 (1), 77– 96, DOI: 10.1007/s41783-018-0049-y
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Taib, N.-A. A. B.; Rahman, M. R.; Huda, D.; Kuok, K. K.; Hamdan, S.; Bakri, M. K. B.; Julaihi, M. R. M. B.; Khan, A. A review on poly lactic acid (PLA) as a biodegradable polymer. Polym. Bull. 2023, 80, 1179– 1213, DOI: 10.1007/s00289-022-04160-y
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A review on polylactic acid (PLA) as a biodegradable polymer
Taib, Nur-Azzah Afifah Binti; Rahman, Md Rezaur; Huda, Durul; Kuok, Kuok King; Hamdan, Sinin; Bakri, Muhammad Khusairy Bin; Julaihi, Muhammad Rafiq Mirza Bin; Khan, Afrasyab
Polymer Bulletin (Heidelberg, Germany) (2023), 80 (2), 1179-1213CODEN: POBUDR; ISSN:0170-0839. (Springer)
A review. Biodegradable plastics are among the most promising materials to replace conventional petroleum-based plastics that have caused many adverse impacts on the environment, such as pollution (land, water, etc.) and global warming. Among a range of biodegradable plastics, poly lactic acid (PLA) is not only widely available but also safe to be decompd. after its usage without polluting the environment. PLA is also in parity with other conventional plastics such as PP, PET in terms of various properties suitable for industrial usage such as mech., phys., biocompatibility and processability. Thus, PLA has become the most used biopolymers in many industries such as agriculture, automotive and packaging by having these characteristics. Its higher demand has contributed to a stable increment in the global PLA market. In fact, over the years, the market for PLA has grown up and will keep on expanding in the future. Overall, the PLA-based bioplastic would be an excellent substitute for the existing conventional plastics in various applications, hence will serve to protect the environment not only from pollution but also work as a sustainable and economical product. This paper will review all the recent related works and literature on PLA as the biodegradable material regarding its properties, usability, productivity and substitute.
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Samantaray, P. K.; Little, A.; Haddleton, D. M.; McNally, T.; Tan, B. W.; Sun, Z. Y.; Huang, W. J.; Ji, Y.; Wan, C. Y. Poly(glycolic acid) (PGA): a versatile building block expanding high performance and sustainable Bioplastic applications. Green Chem. 2020, 22 (13), 4055– 4081, DOI: 10.1039/D0GC01394C
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Poly(glycolic acid) (PGA): a versatile building block expanding high performance and sustainable bioplastic applications
Samantaray, Paresh Kumar; Little, Alastair; Haddleton, David M.; McNally, Tony; Tan, Bowen; Sun, Zhaoyang; Huang, Weijie; Ji, Yang; Wan, Chaoying
Green Chemistry (2020), 22 (13), 4055-4081CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
A review. The concerns about the accumulating plastic waste pollution have stimulated the rapid development of bioplastics, in particular biodegradable bioplastics derived from renewable resources. Driven by a low carbon circular economy, bioplastics prodn. is estd. to reach a 40% share of the plastics market by 2030 (Bioplastics Market Data, 2018). It is expected to substitute petrochem.-based plastics in many applications, from food packaging, pharmaceuticals, electronics, agriculture to textiles. The current biodegradable bioplastics have met challenges in competing with engineering polymers such as PET and Nylon in terms of processing capacity at the industry scale, mech. robustness, thermal resistance, and stability. Poly(glycolic acid) (PGA) has a similar chem. structure to PLA but without the Me side group, which allows the polymer chains to pack together tightly and results in a high degree of crystallinity (45-55%), high thermal stability (Tm = 220-230°C), exceptionally high gas barrier (3 times higher than EVOH), as well as high mech. strength (115 MPa) and stiffness (7 GPa). Meanwhile, PGA is rapidly biodegradable and 100% compostable, showing a similar biodegrdn. profile to cellulose. To date, PGA has been mainly used in the form of copolymers, such as poly(lactic-co-glycolic acid) (PLGA). Its unique properties have often been overlooked and are yet to be explored. This is caused by its intrinsic characteristics such as high hydrophilicity, rapid degrdn., insoly. in most org. solvents and brittleness that have hindered its practical applications. Here we introduced the synthetic chem., processing methods, modification, and applications of PGA, aiming to provide a crit. discussion about the tech. challenges, development opportunities, and solns. for PGA-based materials. The future direction and perspectives for high-performance PGA are proposed. Given its synthesis diversity and unique properties, PGA shows great potential to substitute engineering petrochem.-based polymers for high temp. and high gas barrier packaging applications.
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Takayama, T.; Daigaku, Y.; Ito, H.; Takamori, H. Mechanical properties of bio-absorbable PLA/PGA fiber-reinforced composites. J. Mech. Sci. Technol. 2014, 28 (10), 4151– 4154, DOI: 10.1007/s12206-014-0927-3
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Rodriguez-Gonzalez, F. J.; Ramsay, B. A.; Favis, B. D. High performance LDPE/thermoplastic starch blends: a sustainable alternative to pure polyethylene. Polymer 2003, 44 (5), 1517– 1526, DOI: 10.1016/S0032-3861(02)00907-2
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High performance LDPE/thermoplastic starch blends: a sustainable alternative to pure polyethylene
Rodriguez-Gonzalez, F. J.; Ramsay, B. A.; Favis, B. D.
Polymer (2003), 44 (5), 1517-1526CODEN: POLMAG; ISSN:0032-3861. (Elsevier Science Ltd.)
The properties of LDPE/thermoplastic starch (TPS) blends were investigated. The blends were prepd. by melt mixing in a combined twin-screw/single screw extrusion app. Glycerol is used as the starch plasticizer at 29-40%. Under the one-step processing conditions, a co-continuous LDPE/TPS blend extruded ribbon was prepd. with high elongation at break, modulus and strength in the machine direction. These properties are achieved in the absence of any interfacial modifier and despite the high levels of immiscibility in the polar-nonpolar system. A high degree of transparency is maintained over the entire concn. range due to the similar refractive indexes of components and the virtual absence of interfacial microvoiding. Effective control of the glycerol content, TPS concn. and processing conditions can result in a wide variety of morphol. structures including spherical, fiber-like, highly continuous and co-continuous.
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Madhu, G.; Bhunia, H.; Bajpai, P. K.; Chaudhary, V. Mechanical and morphological properties of high density polyethylene and polylactide blends. J. Polym. Eng. 2014, 34 (9), 813– 821, DOI: 10.1515/polyeng-2013-0174
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Mechanical and morphological properties of high density polyethylene and polylactide blends
Madhu, Gaurav; Bhunia, Haripada; Bajpai, Pramod K.; Chaudhary, Veena
Journal of Polymer Engineering (2014), 34 (9), 813-821CODEN: JPOEEK; ISSN:0334-6447. (Walter de Gruyter GmbH)
Polyblend films were prepd. from high-d. polyethylene (HDPE) and poly(L-lactic acid) (PLLA) up to 20% PLLA by the melt blending method in an extrusion mixer with post-extrusion blown film attachment. The 80/20 (HDPE/PLLA) blend was compatibilized with maleic anhydride grafted polyethylene (PE-g-MA) in varying ratios [up to 8 parts per hundred of resin (phr)]. Tensile properties of the films were evaluated to obtain optimized compn. for packaging applications of both non-compatibilized and compatibilized blends. The compns. HDPE80 (80% HDPE and 20% PLLA) and HD80C4 (80% HDPE, 20% PLLA and 4 phr compatibilizer) were found to be optimum for packaging applications. However, better tensile strength (at yield) and elongation (at break) of 80/20 (HDPE/PLLA) blend were noticed in the presence of PE-g-MA. Further, thermal properties and morphologies of these blends were evaluated. Differential scanning calorimetry (DSC) study revealed that blending does not much affect the cryst. m.p. of HDPE and PLLA, but heat of fusion of 80/20 (HDPE/PLLA) blend was decreased as compared to that of neat HDPE. Spectroscopy studies showed evidence of the introduction of some new groups in the blends and gaining compatibility in the presence of PE-g-MA. The compatibilizer influenced the morphol. of the blends, as apparent from SEM (SEM) and supported by Fourier transform IR (FTIR).
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Guarino, V.; Gentile, G.; Sorrentino, L.; Ambrosio, L. Polycaprolactone: Synthesis, Properties, and Applications. In Encyclopedia of Polymer Science and Technology, 4th ed.; John Wiley & Sons, Inc.: 2002; pp 1– 36.
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Ashton, H. The Incorporation of Nanomaterials into Polymer Media. in Polymer Nanocomposites Handbook; Gupta, R. K., Kennel, E., Kim, K.-J., Eds.; CRC Press, Taylor and Francis: 2010; pp 21– 44.
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