Simultaneously enhancing the crystallization rate and fire retardancy of poly(lactic acid) by using a novel bifunctional additive trimethylamine phenylphosphonate

Facile and Bioinspired Approach from Gallic Acid for the Synthesis of Biobased Flame Retardant Coatings of Basalt Fibers

A sustainable, bioinspired approach to functionalize basalt fibers with an innovative gallic acid (GA)-iron phenyl phosphonate complex (BF-GA-FeP), for the purpose of improving the flame retardancy in composite materials, is developed. BFs were at first pretreated with O3, obtaining surface free hydroxyl groups that allowed the subsequent covalent immobilization of biosourced GA units on the fiber through ester linkages. Phenolic -OH groups of the GA units were then exploited for the complexation of iron phenyl phosphonate, resulting in the target-complex-coated BF fiber (BF-GA-FeP). Microwave plasma atomic emission spectroscopy and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analyses of BF-GA-FeP highlighted an increase in iron content, modification of fiber morphology, and occurrence of phosphorus, respectively. BFs, modified with a low amount of the developed complex, were used to reinforce a poly(lactic acid) (PLA) matrix in the production of a biocomposite (PLA/BF-FeP). PLA/BF-FeP showed a higher thermal stability than neat PLA and PLA reinforced with untreated BFs (PLA/BF), as confirmed by thermogravimetric analysis. The cone calorimeter test highlighted several advantages for PLA/BF-FeP, including a prolonged time to ignition, a reduced time to flame out, an 8% decrease in the peak heat release rate, and a 15% reduced fire propagating index compared to PLA/BF.

Tough and antibacterial poly(l-lactic acid) composites prepared via blending with the bifunctional macromolecular ionomer

In order to expand the application of PLLA in the packaging field, improving its toughness and antibacterial activity has been widely concerned. However, seldom researches can simultaneously efficiently improve the toughness and antibacterial activity of PLLA by adding one kind of additions. To address above problems, the bifunctional branched poly(butylene adipate) ionomer additive (b-PBAUi) was synthesized. For b-PBAUi, its branched structure not only increased the plasticizing effect of additive, but also acted as reaction sites to introduce more antibacterial ionic salt. Due to the special structure of b-PBAUi, PLLA/b-PBAUi blends achieved excellent toughness and antibacterial efficiency. The elongation of blend reached 125 % even by adding 5 wt% b-PBAUi, which was 10 times higher than that of PLLA. From the analysis of phase morphology, it could be found that the microvoids promoting tensile yielding was the main tensile toughening mechanism for PLLA/b-PBAUi blends. In addition, the antibacterial activity of PLLA was significantly improved by adding b-PBAUi. For PLLA/b-PBAUi10 and PLLA/b-PBAUi15, the antibacterial efficiency against E. coli and S. aureus bacteria exceeded 99.0 %. By comprehensive consideration, the optimal blend ratio was achieved by PLLA/b-PBAUi10 due to its excellent toughness and antibacterial efficiency.

Crystallization behaviors regulations and mechanical performances enhancement approaches of polylactic acid (PLA) biodegradable materials modified by organic nucleating agents

Polylactic acid (PLA) has attracted much attention because of its good biocompatibility, biodegradability, and mechanical properties. However, the slow crystallization rate of PLA during molding leads to its poor heat resistance, which limit its diffusion for many industrial applications. In this review, the relationship between PLA crystallization and its molecular structure and processing conditions is summarized. From the perspective of the regulation of PLA crystallization by organic nucleating agents, the research progress of organic micromolecule (e.g., esters, amides, and hydrazides), organic salt, supramolecular, and macromolecule nucleating agents on the crystallization behavior of PLA is mainly introduced. The nucleation mechanism of PLA is expounded by organic nucleating agents, and the effect of the interaction force between organic nucleating agents and PLA molecular chains on the crystallization behavior of PLA is analyzed. The effects of the crystallization behavior of PLA on its mechanical properties and heat resistance are discussed. It will provide a theoretical reference for the development and application of high-efficiency nucleating agents.

Synergistic effect of poly(ionic liquid) and phosphoramide on flame retardancy and crystallization of poly(lactic acid)

Crystallinity and flame retardancy are two key properties for poly(lactic acid)(PLA) in applications. In this paper, a quaternary phosphonium salt poly(ionic liquid) (PIL) and a phosphamide (POFA) were prepared. The PIL, POFA and their blend were used to regulate the flame retardancy and crystallization behaviors of PLA using the limiting oxygen index, UL-94 vertical burning, and thermogravimetric analysis, and differential scanning calorimetry etc. The results showed that a synergistic effect exists between PIL and POFA on flame retardancy. When 6 wt% PIL/POFA (2/1) was added into PLA, its LOI value is 28.0 vol%, and achieves the UL-94 V-0 rating while the PLA composites containing 6 wt% PIL or POFA just achieve the UL-94 V2. The PIL/POFA improves the flame retardancy of PLA by melting-away mode. In addition, the crystallization rate of PLA containing PIL/POFA is faster than that of PLA/PIL and PLA/POFA. The degradation of PLA induced by PIL/POFA produces some small molecular oligomers, which enhances the molecular chain mobility and rearrangement, thus contributes to better flame retardancy and faster crystallization.

Development of multifunctional highly-efficient bio-based fire-retardant poly(lactic acid) composites for simultaneously improving thermal, crystallization and fire safety properties

Currently, it is still a huge challenge to prepare high performance eco-friendly poly(lactic acid) (PLA) with high thermal stability, good processability, excellent crystallization behavior, good transparency and highly-efficient fire safety. In this paper, a novel bio-based nucleation agent N-(furan-2-ylmethyl)-P,P-diphenylphosphinic amide (FPPA) was prepared and used for the fabrication of fire safety PLA/FPPA composites. The chemical structure of FPPA was measured by FTIR, NMR and MS. Further, the crystallization behavior, thermal stability, fire safety and mechanical properties of PLA/FPPA composites were performed by TGA, DSC, polarization microscope, LOI, UL94, cone calorimeter, DMA and, SEM, Raman, GC-MS, and TGA-FTIR. The results showed that the multifunctional FPPA not only had a high thermal stability and was a good nucleation agent for PLA. Moreover, only loading of 3 wt% FPPA increased the LOI of PLA from 19.0 to 33.8 % with UL-94 V-0 classification. Furthermore, the heat release rate and total heat release values of PLA/3%FPPA composite reduced by 6.3 % and 15.3 % in cone-calorimeter test. Such high fire safety was mainly attributed to specific fire safety radicals due to thermal degradation of FPPA to interrupt composites burning in gas phase. Besides, transparency and mechanical properties were almost not changed because of low loading of FPPA in PLA. This multifunctional bio-based fire-retardant for PLA with good comprehensive performance promises broad application in engineering electronics, automobiles, 3D printing and construction materials.