Diisocyanate-Induced Dynamic Vulcanization of Difunctional Fatty Acids toward Mechanically Robust PLA Blends with Enhanced Luminescence Emission

A generalizable reactive blending strategy to construct flame-retardant, mechanically-strong and toughened poly(L-lactic acid) bioplastics

Poly(L-lactic acid) (PLA) is an environmentally-friendly bioplastic with high mechanical strength, but suffers from inherent flammability and poor toughness. Many tougheners have been reported for PLA, but their synthesis usually involves organic solvents, and they tend to dramatically reduce the mechanical strength and cannot settle the flammability matter. Herein, we develop strong, tough, and flame-retardant PLA composites by reactive blending PLA, 6-((double (2-hydroxyethyl) amino) methyl) dibenzo [c, e] [1,2] oxyphosphate acid 6-oxide (DHDP) and diphenylmethane diisocyanate (MDI) and define it PLA/xGH, where x indicates that the molar ratio of -NCO group in MDI to -OH group in PLA and DHDP is 1.0x: 1. This fabrication requires no solvents. PLA/2GH with a -NCO/-OH molar ratio of 1.02: 1 maintains high tensile strength of 63.0 MPa and achieves a 23.4 % increase in impact strength compared to PLA due to the incorporation of rigid polyurethane chain segment. The vertical combustion (UL-94) classification and limiting oxygen index (LOI) of PLA/2GH reaches V-0 and 29.8 %, respectively, because DHDP and MDI function in gas and condensed phases. This study displays a generalizable strategy to create flame-retardant bioplastics with great mechanical performances by the in-situ formation of P/N-containing polyurethane segment within PLA.

Soft-hard dual nanophases: a facile strategy for polymer strengthening and toughening

Polymers often face a trade-off between stiffness and extensibility-for example, toughening rigid polymers by incorporating plasticizers or flexible polymers leads to strikingly decreased stiffness. Herein, we circumvent this long-standing tricky dilemma in materials science via constructing soft-hard dual nanophases in polymers. As-fabricated dual-nanophase PLA shows a high yield strength of 69.1 ± 4.4 MPa, a large extensibility of 279.1 ± 25.5%, and a super toughness of 115.2 ± 10.3 MJ m-3, which are 1.2, 48 and 82 times, respectively, those of neat PLA. Combined high stiffness, large ductility, and super toughness are unprecedented for PLA and enable bio-sourced PLA to replace petroleum-based resins such as PP, PET and PC. Besides, soft-hard dual nanophases in polymers are rarely reported due to significant constraints in terms of modifier dispersion/aggregation, interfacial regulation, and processing difficulties. The construction strategy described herein, combining controlled annealing and a well-designed plasticizer, can efficiently construct soft-hard dual nanophases in polymers, which will greatly advance the nanostructure design of polymers. More importantly, the proposed strategy for materials design will be widely applicable to industrial manufacturing in terms of nanophase construction and interfacial optimization due to the simplicity and availability at a large scale. We envision that this work offers an innovative and facile strategy to circumvent the trade-off between stiffness and extensibility and to advance the nanostructure design of high-performance polymers in a manner applicable to industrial manufacturing.

In-situ self-crosslinking strategy for super-tough polylactic acid/ bio-based polyurethane blends

As a bio-based degradable plastic, polylactic acid (PLA) is highly commercialized, but its inherent brittleness limits its widespread use. In-situ polymerization techniques are effective in improving the toughness of PLA. However, the enhancement of the toughening effect in polyurethanes (PUs) through in-situ self-crosslinking still requires improvement and heavily relies on petroleum-derived feedstocks in certain approaches. In this paper, 1,3-polypropanediol (PO3G) of bio-based origin rather than conventional polyols like polyethylene glycol (PEG) and poly propylene glycol (PPG) was used. PLA/PO3G-PU blends were prepared via an in-situ self-crosslinking strategy. With a notch impact and tensile strength of 55.95 kJ/m2 and 47.77 MPa (a retention rate of 68.9 % compared with pure PLA), respectively, PLA/PO3G-PU blends achieved a better balance between stiffness and toughness. This work provides a new option for PLA to achieve a stiffness-toughness balance and get rid of dependence on petrochemical resources.

Preparation of degradable chemically cross-linked polylactic acid films and its application on disposable straws

The semi-rigidity of the polylactic acid (PLA) molecular chain makes it brittle, poor impact resistance and barrier properties, which severely limits its practical applications. In this paper, a bio-based reactive plasticizer epoxy soybean oil (ESO) was used to improve the mechanical and barrier properties of maleic anhydride grafted polylactic acid (MAPLA) by the chemical reaction between the epoxy and anhydride group. Firstly, the optimum curing conditions were 93.5 °C, 100 °C, and 110.8 °C for 2 h. The effects of different mass fractions of ESO on the properties of MAPLA-ESO (ME) films were systematically investigated. It was found that when the content of ESO was 10 wt%, the tensile properties of the resulting ME films were the best, with a tensile strength of 35.2 MPa. And it had an elongation at break of 20.0 % and toughness of 5.4 MJ/m3, which increased to 690 % and 675 %, respectively, compared with pure MAPLA films. The chemically crosslinked ME films also displayed excellent water resistance, well degradation, low migration properties, and better performance than that of commercial paper straws and PLA straws, exhibiting great application potential as degradable disposable straws. Therefore, this work provides an effective way to develop high-performance, green, and degradable PLA films and products.

Impact fracture mechanism and heat deflection temperature of PLA/PEICT blends reinforced by glass fiber

To enhance the crack propagation and initiation properties and heat deflection temperature of poly(lactic acid) (PLA), PLA/poly(1,4-cyclohexanedimethylene isosorbide terephthalate) (PEICT) blend systems were prepared and glass fibers (GF) were incorporated as reinforcements. Due to high shear force during extrusion and injection molding the length of GF was reduced and was oriented towards the flow direction. Although the reinforcing effect of the GF deviated from the theoretical values calculated by the Halpin-Tsai equation, both tensile and flexural properties were greatly enhanced with increasing GF content. Dynamic mechanical and thermal testing showed improved storage modulus throughout the entire temperature range showing outstanding reinforcing ability. By incorporating GF into the PLA/PEICT blend, the crack propagation and initiation properties were enhanced compared to pristine PLA. Such an increase in crack propagation properties was the result of enhanced modulus with the added GF. Moreover, because of the increased modulus, the heat deflection temperatures of the GF reinforced blends were drastically increased showing a value of 91.4 °C at 20 wt% GF loading. The high performance reached by the biomass-based composites developed in this research shows great possibility of replacing these conventional petroleum-based polymer systems.

Designing Strong, Tough, Fluorescent, and UV-Shielding PLA Materials by Incorporating a Phenolic Compound-Based Multifunctional Modifier

The realization of high stiffness, high extensibility, and multi-functions for polylactic acid (PLA) is a vital issue for its practical applications. Herein, hydroxyalkylated tannin acid (mTA), a phenolic compound-based modifier with plentiful flat aromatic structures and flexible isopropanol oligomers, is designed and fabricated to act as the multifunctional modifier for PLA. The mTA exhibits the capability of emitting fluorescence and blocking UV light due to the combination of flat aromatic structures and plentiful flexible chains. Besides, mTA with high grafting degree (h-mTA) shows an excellent compatibility to PLA due to the hydrogen bonding interface and the high affinity of grafted isopropanol oligomers to PLA. As a result, the as-prepared PLA/h-mTA20 composite exhibits a strikingly improved extensibility by 61.2 times while maintaining the high yield strength of PLA. Moreover, PLA/h-mTA can serve as a fluorescent material with multi-mode responsiveness as well as a UV-shielding material with high transparency. We envision that this work opens a novel yet facile way to prepare a strong, tough, and multifunctional PLA material with expanded application scopes and will promote the practical applications of phenolic compounds in polymers.