PLA Backbone Research Articles

Bioelectrets in Electrospun Bimodal Poly(lactic acid) Fibers: Realization of Multiple Mechanisms for Efficient and Long-Term Filtration of Fine PMs

Despite the great potential in fabrication of biodegradable and eco-friendly air filters by electrospinning poly(lactic acid) (PLA) membranes, the filtering performance is frequently dwarfed by inadequate physical sieving or electrostatic adsorption mechanisms to capture airborne particulate matters (PMs). Here, using the parallel spinning approach, the unique micro/nanoscale architecture was established by conjugation of neighboring PLA nanofibers, creating bimodal fibers in electrospun PLA membranes for the enhanced slip effect to significantly reduce the air resistance. Moreover, the bone-like nanocrystalline hydroxyapatite bioelectret (HABE) was exploited to enhance the dielectric and polarization properties of electrospun PLA, accompanied by the controlled generation of junctions induced by the microaggregation of HABE (10-30 wt %). The incorporated HABE was supposed to orderly align in the applied E-field and largely promote the charging capability and surface potential, gradually increasing to 7.2 kV from the lowest level of 2.5 kV for pure PLA. This was mainly attributed to HABE-induced orientation of PLA backbone chains and C═O dipoles, as well as the interfacial charges trapped at the interphases of HABE-PLA and crystalline region-amorphous PLA. Given the multiple capturing mechanisms, the micro/nanostructured PLA/HABE membranes were characterized by excellent and sustainable filtering performance, e.g., the filtration efficiency of PM0.3 was promoted from 59.38% for pure PLA to 94.38% after addition of 30 wt % HABE at a moderate airflow capacity of 32 L/min and from 30.78 to 83.75% at the highest level of 85 L/min. It is of interest that the pressure drop was significantly decreased, mainly arising from the slip effect between the ultrafine nanofibers and conjugated microfibers. The proposed combination of the nanostructured electret and the multistructuring strategy offers the function integration of efficient filtration and low resistance that are highly useful to pursue fully biodegradable filters.

Poly(Lactic Acid)-Based Graft Copolymers: Syntheses Strategies and Improvement of Properties for Biomedical and Environmentally Friendly Applications: A Review.

As a potential replacement for petroleum-based plastics, biodegradable bio-based polymers such as poly(lactic acid) (PLA) have received much attention in recent years. PLA is a biodegradable polymer with major applications in packaging and medicine. Unfortunately, PLA is less flexible and has less impact resistance than petroleum-based plastics. To improve the mechanical properties of PLA, PLA-based blends are very often used, but the outcome does not meet expectations because of the non-compatibility of the polymer blends. From a chemical point of view, the use of graft copolymers as a compatibilizer with a PLA backbone bearing side chains is an interesting option for improving the compatibility of these blends, which remains challenging. This review article reports on the various graft copolymers based on a PLA backbone and their syntheses following two chemical strategies: the synthesis and polymerization of modified lactide or direct chemical post-polymerization modification of PLA. The main applications of these PLA graft copolymers in the environmental and biomedical fields are presented.

Influence of the Degradation Medium on Water Uptake, Morphology, and Chemical Structure of Poly(Lactic Acid)-Sisal Bio-Composites.

A series of poly(lactic acid) (PLA) and poly(lactic acid)-based bio-composites (sisal PLA) were prepared and studied by spectroscopic and microscopic techniques as such and after immersion at room temperature in different degradation mediums (i.e., distilled and natural sea water and solutions at pH = 2, 6, and 8). In these conditions, some of their macroscopic and microscopic properties were monitored during a period of 30 days. Water absorption increased with the increasing fiber content regardless of the immersion medium. The maximum water absorption was achieved at pH = 8 (~16%), indicating a more severe action of the alkaline mediums on the samples. The diffusivity, D, of PLA decreased with the addition of fibers and acidic mediums showed higher D, indicating higher diffusivity of water through the specimens with respect to those submerged in moderate or alkaline mediums. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analysis evidenced a weak interaction between the PLA matrix and the sisal fibers. Very limited degradation phenomena occur in our conditions: Despite some changes in the microstructure, the PLA backbone seems to be largely resistant to hydrolysis, almost regardless of the pH value and even at the highest sisal content.

Enhancing the Crystallization Performance of Poly(L-lactide) by Intramolecular Hybridizing with Tunable Self-assembly-type Oxalamide Segments

In this work, hydroxyl-terminated oxalamide compounds N1,N2-bis(2-hydroxyethyl)oxalamide (OXA1) and N1, N1′-(ethane-1,2-diyl)bis(N2-(2-hydroxyethyl)oxalamide (OXA2) were synthesized to initiate the ring-opening polymerization of L-lactide for preparation of oxalamide-hybridized poly(L-lactide) (PLAOXA), i.e., PLAOXA1 and PLAOXA2. The crystallization properties of PLA were improved by the self-assembly of the oxalamide segments in PLAOXA which served as the initial heterogeneous nuclei. The crystal growth kinetics was studied by Hoffman-Lauritzen theory and it revealed that the nucleation energy barrier of PLAOXA1 and PLAOXA2 was lower than that of PLA. Consequently, PLAOXA could crystallize much faster than PLA, accompanied with a decrease in spherulite size and half-life crystallization time by 74.8% and 86.5% (T = 125 °C), respectively. In addition, the final crystallinity of PLAOXA1 and PLAOXA2 was 6 and 8 times higher, respectively, in comparison with that of neat PLA under a controlled cooling rate of 10 °C/min. The results demonstrate that the hybridization of oxalamide segments in PLA backbone will serve as the self-heteronucleation for promoting the crystallization rate. The higher the content of oxalamide segments (PLAOXA2 compared with PLAOXA1) is, the stronger the promotion effect will be. Therefore, this study may provide a universal approach by hybridizing macromolecular structure to facilitate the crystallization of semi-crystalline polymer materials.

Enhanced impact strength of compatibilized poly(lactic acid)/polyamide 11 blends by a crosslinking agent

AbstractMaleated poly(lactic acid) (PLA‐g‐MA) was prepared through melt grafting of maleic anhydride onto a PLA backbone with the aid of a radical initiator. PLA‐g‐MA thus formed was incorporated into PLA/polyamide 11 (PA11) blends as a reactive compatibilizer. By morphological observation, it was assessed that PLA‐g‐MA lowered the interfacial energy and strengthened the interface between PLA and PA11. However, the compatibilized PLA/PA11 blends did not show significant improvement of impact strength compared with noncompatibilized PLA/PA11 blends. Measurements of the molecular weight and impact strength of PLAs compounded with various amounts of radical initiators revealed that decreased molecular weight of PLA by the radical initiator used for the preparation of PLA‐g‐MA is responsible for this unexpected result. To compensate the decrease of the molecular weight, a crosslinking agent was incorporated in the preparation step of PLA‐g‐MA. It was found that the crosslinking agent is effective in preventing the molecular weight reduction. As a result, the impact strength of the PLA/PA11 blend was enhanced to a great extent by the PLA‐g‐MA prepared with the crosslinking agent.

Polylactide with improved optical property by introducing natural functional substance: Aloe-emodin

The PLA materials with improved optical property and derived from renewable resources were synthesized through ring-opening polymerization using natural aloe-emodin, having anthraquinone structure and alcoholic hydroxyl group, as initiator. The chemical bonding of the aloe-emodin unit on PLA backbone provided the PLA with the function of absorbing UV light and would avoid the migration of aloe-emodin during the lifetime of PLA materials. The chemical structure of the new PLA was confirmed by NMR and the content of aloe-emodin was evaluated by UV–Vis absorption spectra. By investigating the structural changes and the variation of average molecular weight (Mn) during the UV-irradiation test, it was found that the aloe-emodin unit could enhance the UV-stability of the polylactide. The molecular weight remained about 80% for aloe-emodin capped PLA after UV irradiation (PLA-E400), while it was only 50% for PLA-C400 without aloe-emodin. A small amount of aloe-emodin could enhance the UV block effect of PLA film. When covered with aloe-emodin functionalized PLA film, the optical damage rate of β-carotene decreased to one-fifth of that for the uncovered one. In addition, aloe-emodin showed little influence on the biodegradation of PLA.

Star Shaped Long Chain Branched Poly (lactic acid) Prepared by Melt Transesterification with Trimethylolpropane Triacrylate and Nano-ZnO.

Long chain branched poly (lactic acid) (LCBPLA) was prepared via transesterification between high molecular weight poly (lactic acid) (PLA) and low molar mass monomer trimethylolpropane triacrylate (TMPTA) during melt blending in the presence of zinc oxide nanoparticles (nano-ZnO) as a transesterification accelerant in a torque rheometer. Compared with the traditional processing methods, this novel way is high-efficiency, environmentally friendly, and gel-free. The results revealed that chain restructuring reactions occurred and TMPTA was grafted onto the PLA backbone. The topological structures of LCBPLA were verified and investigated in detail. It was found that the concentration of the accelerants and the sampling occasion had very important roles in the occurrence of branching structures. When the nano-ZnO dosage was 0.4 phr and PLA was sampled at the time corresponding to the reaction peak in the torque curve, PLA exhibited a star-shaped topological structure with a high branching degree which could obviously affect the melt strength, extrusion foaming performances, and crystallization behaviors. Compared with pristine PLA, LCBPLA showed a higher melt strength, smaller cell diameter, and slower crystallization speed owing to the synergistic effects of nano-ZnO and the long chain branches introduced by the transesterification reaction in the system. However, severe degradation of the LCBPLAs would take place under a mixing time that was too long and lots of short linear chains generated due to the excessive transesterification reaction, with a sharp decline in melt strength.

Reactive plasticization of poly(lactide) with epoxy functionalized cardanol

New biobased plasticizers made of di‐functional glycidyl ether epoxy cardanol (ECard) were investigated to improve the ductility of renewable poly(lactide) (PLA). Compatibility between PLA and ECard was achieved out through in situ reactive grafting strategy catalyzed with Ethyltriphenyl phosphonium bromide (ETPB) using twin‐screw extruder. In absence of catalyst, ECard forms domain ill‐dispersed in the PLA matrix due to the high incompatibility between both phases. When ETPB is added as catalyst domain size distribution of the plasticizer decreased, indicating an enhanced compatibility due to the reactive grafting of a fraction of ECard plasticizer onto PLA backbone. Although all plasticized PLA specimens exhibit lower glass transition temperature, lower elastic/tensile modulus, lower yield stress, and higher strain at break, the reactive blend containing the lowest amount of catalyst, that is, 0.02 phr, exhibited the highest ductility behavior. POLYM. ENG. SCI., 58:E64–E72, 2018. © 2017 Society of Plastics Engineers

Effect of Maleic Anhydride-Modified Poly(lactic acid) on the Properties of Its Hybrid Fiber Biocomposites.

This work investigated the effect of maleic anhydride (MA)-modified poly(lactic acid) (PLA), which is melt-blended with different untreated and aqueous borax (BR)-treated hybrid oil palm empty fruit bunch fibers (EFBF)/Kenaf core fibers (KCF), and compression-molded into corresponding hybrid biocomposites. These hybrid systems includes BR-treated EFBF/BR-treated KCF reinforced MA-modified PLA i.e., BR(EFBF-KCF)-MAPLA, BR-treated EFBF/BR-treated KCF reinforced unmodified PLA i.e., BR(EFBF-KCF)-PLA, untreated EFBF/untreated KCF reinforced MA-modified PLA i.e., EFBF-KCF-MAPLA, and untreated EFBF/untreated KCF reinforced unmodified PLA i.e., EFBF-KCF-PLA respectively. Characterizations of the hybrid systems revealed that optimal mechanical, physical, morphological, thermal and dynamic mechanical properties were provided by the BR(EFBF-KCF)-MAPLA, resulting from improved interface adhesion, consequent of the synergistic influence of BR treatment of natural fibers, and the compatibilization effect provided by the MA-modified PLA. The grafting degree and efficiency of MA onto the PLA backbone was appreciable, as indicated by direct titration, and through monitoring using Fourier Transform Infrared Spectroscopy (FTIR); thus the MA-modified PLA facilitated the formation of strong interface adhesion with the BR-treated hybrid fibers. The BR(EFBF-KCF)-MAPLA showed promising properties for usage as a bio-inspired, and sustainable alternative fiberboard article.

Post-polymerization modification of poly(lactic acid) via radical grafting with itaconic anhydride

Poly(lactic acid) (PLA) was functionalized via radical grafting with itaconic anhydride (IAH) in melt. Reaction was initiated using 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (L101). Experiments were achieved in order to determine the relationship between reaction conditions and grafting yield, whereas different concentrations of IAH (0.5–10wt%) and L101 (0.1–2wt%) were used for reaction. Reaction temperature 190°C (calculated according to Arrhenius equation) guaranteed complete decomposition of L101 upon reaction period 6min. Grafted IAH onto PLA backbone was proved by infrared spectroscopy (FTIR). Structure analysis also proved IAH isomerization to citraconic anhydride (CAH) which affects monomer reactivity at processing temperature. Homopolymerization of IAH was predicted regarding thermal stability of extracted byproducts compared to poly(itaconic anhydride) (PIAH) prepared by radical polymerization in solution. Acid–base titration proved that amount of grafted IAH increases with increasing IAH and L101 concentrations. However, increasing IAH and L101 concentrations lead to higher extent of undesired reactions which were detected by melt flow rate measuring (MFR).

Toughening of poly(lactide) using polyethylene glycol methyl ether acrylate: Reactive versus physical blending

To design high‐performance poly(lactide)‐based materials (PLA‐based) with improved toughness, two approaches based on the reactive extrusion (REx) process are investigated and compared in the present study. The first approach relies upon a two‐step procedure using a REx‐polymerized poly(ethylene glycol) methyl ether acrylate, i.e., poly(AcrylPEG), as a highly‐branched and compatible impact modifier for PLA. The free‐radical polymerization proves to be very efficient with a peroxide initiator concentration of 1 wt%. The as‐produced poly(AcrylPEG) is then melt‐blended with PLA by extrusion. The resulting materials exhibit largely increase impact resistance (ca. 35 kJ/m2) in presence of 20 wt% poly(AcrylPEG) in comparison with neat PLA (2.7 kJ/m2), while moderate ductility (tensile elongation at break <40%) and limited plasticization effect are observed. The second “one‐step” approach consists in in situ grafting of AcrylPEG onto PLA backbone via a one‐stage REx. The resulting materials exhibit substantially improved impact resistance (ca. 102 kJ/m2) for AcrylPEG loading of 20 wt%, high ductility (tensile elongation at break of ca. 150%) and efficient plasticization. A detailed characterization of the morphology of the materials has been performed using PF‐QNM‐AFM to better elucidate the structure‐property relationships. POLYM. ENG. SCI., 55:1408–1419, 2015. © 2015 Society of Plastics Engineers

Conversion of poly(lactic acid) to lactide via microwave assisted pyrolysis

Microwave assisted pyrolysis (MAP) of poly(lactic acid) (PLA) was performed using different MW absorbers (tire, carbon, or Fe), apparatus set-up, and MW power, obtaining a liquid rich in 3,6-dimethyl-1,4-dioxan-2,5-dione (lactide) and other oxygenated organic compounds. Pure form of l-lactide was separated from the collected liquids while the meso-form of lactide was present in liquid and identified through GC–MS analysis. Up to 27.7% of lactide was formed and might be recovered. Furthermore simple acids such as acetic acid and propionic acid (up to 17.1%), carbonyl compounds, and fragments of PLA backbone randomly cleaved were present in liquids.The pyrolysis of PLA in the presence of other polymers, which might pyrolyze to aromatic compounds, such as those present in tires, gave cross reactions in the course of the pyrolysis affecting both yield and characteristics of liquid. Aromatic compounds formed from tire pyrolysis prevented the precipitation of lactide.

Toward faster degradation for natural fiber reinforced poly(lactic acid) biocomposites by enhancing the hydrolysis-induced surface erosion

The poor and uncontrollable biodegradability of poly(lactic acid) (PLA)-based materials is one of the fundamental limitations for widening their applications. To regulate the degradation of PLA/ramie fiber biocomposites, the hydrophilicity of the composites was modified to attract more water attack by introducing water-soluble poly(ethylene glycol) (PEG). Analyses by characterization of sample size, weight loss and microstructure offered intensive information on the degradation behavior of PLA biocomposites. It was revealed that PEG indeed significantly enhanced the surface erosion process and thus facilitated the degradation rate. The biocomposite bar containing 15 wt% PEG completed degradation within 50 days, while only ~50 wt% mass lost for the control biocomposite sample without PEG. Morphological observation confirmed that PEG accelerated the penetration of outside water from the surface to the center driven by the diffusion-in process, which subsequently boosted the hydrolytic action of the PLA backbone ester groups. Our results indicated that the PEG induced water penetration governed the overall degradation kinetics. As a strong response to the degradation, the stiffness of the biocomposite bars suffered from drastic decrease while T g varied in a climbing trend within the early stage. Microscopic examination of degradation solution formed during hydrolytic degradation of the PLA biocomposites suggested oligomers or lactic acid monomers were released to the solutions. It was of great interest to observe PEG dissolved in the alkaline solution speeded the ramie fibers breaking down to tiny fragments and cellulose macromolecules which further regenerated into cellulose aggregates in various fantastic appearances like coral-like leaves and pine needles. Our success in regulating the degradation of PLA biocomposites also provides an instructive approach for other PLA based materials.

Tunable and Durable Toughening of Polylactide Materials Via Reactive Extrusion

To tune the toughness of PLA, a novel pathway to chemically modify PLA via reactive extrusion in the presence of “reactive” PEG derivatives is proposed. PEG methyl ether methacrylate (MAPEG) and PEG methyl ether acrylate (AcrylPEG) are melt‐mixed and extruded with PLA in the presence of 2,5‐dimethyl‐2,5‐di(tert‐butylperoxy)hexane (L101) as a free‐radical initiator. Molecular characterization reveals that about 20 and 65%, respectively, of the initially introduced MAPEG and AcrylPEG can be grafted onto the PLA backbone. The plasticization effect is demonstrated by a significant decrease of the glass transition temperature and storage modulus together with a significant increase of the elongation at break as compared to neat PLA.

Reactive functionalization of poly(lactic acid), PLA: Effects of the reactive modifier, initiator and processing conditions on the final grafted maleic anhydride content and molecular weight of PLA

Abstract A response surface methodology (RSM) design was used to analyze the effects of maleic anhydride (MA) and 2,5-bis( tert -butylperoxy)-2,5-dimethyl hexane (Luperox or L101) content, and TSE screw speed on the degree of grafted MA (MA g ) and number average molecular weight ( M n ) of maleated PLA (PLA- g -MA), which can be used as a reactive compatibilizer in production of PLA blends with various components. PLA- g -MA's FTIR peaks indicated that MA was grafted onto the PLA backbone and oligomeric MA was also present. A maximum of 0.52 wt% MA g determined by titration was achieved at the expense of a 50% reduction of M n and an increase in the polydispersity index to around 2.0. Generally, increasing L101 increased the degree of grafting and decreased M n . L101 and MA g had a large effect on the stability of PLA- g -MA's M n during storage. Nominally, amounts of MA equal to 4.5 wt%, L101 between 0.45 and 0.65 wt%, and screw speed of 20 rpm provided the optimal conditions for grafting MA onto PLA.

Structural Characterization of Serial Novel Star-Shaped Biodegradable Material Poly(lactic acid-<i>co</i>-melamine)

Using flame retardant melamine (MA) as a new aromatic core, biodegradable material poly (lactic acid-co-melamine) [P(LA-co-MA)] with different molar feed ratios are synthesized via direct melt copolycondensation. The structures of P(LA-co-MA) s are characterized by FT-IR,1H-NMR,13C-NMR and GPC. The results indicate that MA moiety as the core is incorporated into the PLA backbone as expected, and the obtained products are copolymers indeed.

Increased covalent conjugation of a model antigen to poly(lactic acid)-g-maleic anhydride nanoparticles compared to bare poly(lactic acid) nanoparticles

Maleic anhydride (MA) grafted poly(lactic acid) (PLA) (PLA-g-MA) was synthesized from PLA. Proton nuclear magnetic resonance confirmed the grafting of the MA. PLA-g-MA and PLA were used to prepare polymeric nanoparticles. Particle size distributions were measured by dynamic light scattering, and colloidal stability was determined by (zeta) ζ-potential. The ζ-potential becomes more negative for PLA-g-MA than PLA nanoparticle dispersions, due to the presence of deprotonated carboxylic acid groups on the backbone of the PLA and confirms the MA grafting results. Maleic anhydride grafted on PLA backbone improves the covalent conjugation with ovalbumin (OVA) compared to OVA physically adsorbed on the particles. The chemical conjugation was carried out via amide linkages between the carboxylic groups of the nanoparticles, activated with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, and the amino groups of the protein. The amount of protein conjugated was measured by using the bicinchoninic acid method and is threefold higher compared to the adsorbed OVA. Moreover, the PLA-g-MA nanoparticles increased the amount of conjugated OVA by 36 wt% compared to PLA nanoparticles. OVA adsorption and OVA conjugation provided colloidal dispersions with excellent stability.

Improved antifungal activity of itraconazole-loaded PEG/PLA nanoparticles

Poly(ethylene glycol)/polylactic acid (PEG/PLA) nanoparticles (NPs) containing the hydrophobic antifungal itraconazole (ITZ) were developed to provide a controlled release pattern of ITZ as well as to improve its aqueous dispersibility and hence enhance its antifungal action. Two PEG/PLA copolymers (PEGylated PLA polymers) were used in this study; branched PEGylated polymer in which PEG was grafted on PLA backbone at 7% (mol/mol of lactic acid monomer), PEG7%-g-PLA, and multiblock copolymer of PLA and PEG, (PLA–PEG–PLA)n with nearly similar PEG insertion ratio and similar PEG chain length. ITZ-loaded PLA NPs were also prepared and included in this study as a control. ITZ-NPs were prepared from a 1 : 1 w/w blend of PLA and each PEGylated polymer either PEG7%-g-PLA or (PLA–PEG–PLA)n using an oil-in-water emulsion evaporation method. The NPs morphology, size and size distribution, zeta potential, loading efficiency, release profile and antifungal activity were characterized. All ITZ-NPs were nearly spherical with smooth surface and showed less aggregating tendency with a size range of 185–285 nm. All ITZ-NPs measured nearly neutral zeta potential values close to 0 mV. The % LE of ITZ was ∼94% for PEG7%-g-PLA NPs and ∼83% for (PLA–PEG–PLA)n at 15.3% w/w theoretical loading. PEG/PLA NPs were stable over time regarding size and size distribution and % ITZ loading efficiency (% LE). ITZ release showed an initial burst followed by a gradual release profile for ITZ-NPs over 5 days. (PLA–PEG–PLA)n NPs exhibited faster release rates than PEG7%-g-PLA NPs particularly at the last 2 days. Differential scanning calorimetry and powder X-ray diffractometry data confirmed that ITZ exists in an amorphous state or a solid solution state into the NPs matrix. Fourier transform infrared revealed the possibility of chemical interaction between ITZ and the NPs matrix polymer indicating the successful entrapment of ITZ inside the particles. In haemolysis test, ITZ-NPs caused mild haemolysis over the concentration range (5–20 µg/mL) compared to free ITZ, indicating better safety profile of ITZ-NPs. ITZ-loaded PEG/PLA NPs inhibited fungal growth more efficiently than either free ITZ or ITZ-loaded PLA NPs. Our results suggest that PEG/PLA–ITZ could be used efficiently as a nanocarrier to improve the aqueous dispersibility of ITZ, control its release over time and, thereby, enhance its antifungal efficacy.

Melt Strength and Rheological Properties of Biodegradable Poly(Lactic Aacid) Modified via Alkyl Radical-Based Reactive Extrusion Processes

Poly(lactic acid) (PLA) has been modified using twin-screw reactive extrusion to improve its melt properties and crystallinity. In this work lauroyl peroxide was used as an alkyl free radical source, abstracting hydrogen atoms from the PLA backbone leading to branching and chain extension reactions. Once the linear viscoelastic region was determined for these polymers, changes in dynamic rheology (dynamic viscosity real and loss modulus) were measured. Gel permeation chromatography showed that the molecular weight and polydispersity increased to a maximum with the addition of 1.00 and 0.50 wt% peroxide, respectively. Low temperature β transitions in dynamical mechanical thermal traces gave further evidence that branching had also occurred. Gottfert Rheotens measurements showed a three fold increase in melt strength due to both increased chain length and branching. Thermal analysis showed the level of crystallisation had decreased also possibly due to branching. Reductions in crystallinity and improved melt strength are known to be critical for film and foam formation.

Inherent flame retardation of bio-based poly(lactic acid) by incorporating phosphorus linked pendent group into the backbone

The molecular design for inherently flame-retardant poly(lactic acid) (IFR-PLA) was outlined and achieved by chemically incorporating an effective organophophorus-type flame retardant (FR) into the PLA backbone via the chain extension of the dihydroxyl-terminated prepolymer with 1, 6-hexamethylene diisocyanate (HDI). The structure of IFR-PLA was characterized by 1H- and 31P-nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. IFR-PLA was further blended with the commercial PLA to prepare flame retardant PLA blends (PLA-FR blend). The relevant properties of IFR-PLA and PLA-FR blends were evaluated by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), limiting oxygen index (LOI) measurements and UL-94 tests. The thermal analysis revealed that the char yield of IFR-PLA and PLA-FR blend above 400 °C was greatly enhanced compared to that of pure PLA. The LOI value was significantly improved from 19 for pure PLA to 29 when 1 wt% of phosphorus content was introduced and all IFR-PLA samples achieved V-0 rating in the UL-94 tests. PLA-FR blends had an LOI value of 25–26 and UL-94 V-2 rating at 20 wt% of IFR-PLA content. The tensile strength of all the FR PLA systems was ca. 60 MPa. The method used in this study provided a novel route to permanently flame retard PLA.