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Wood is an important renewable material exhibiting excellent physical and mechanical properties, environmental friendliness, and sustainability, and has been widely applied in daily life. However, its inherent flammability and susceptibility to fungal attack greatly limit its application in many areas. Use of fire-retardant coatings and preservatives has endowed wood with improved safety performance; importantly, the cooperative effect of dual treatments on the burning behavior and flame retardancy of wood needs to be better understood. Here, a two-step treatment for wood is proposed, with a copper–boron preservative (CBP) and a fire-retardant coating. The thermal degradation and burning behavior of treated wood were investigated. The CBP formed a physical barrier on the wood surface, facilitating a charring process at high temperatures and thus suppressing the release of heat and smoke. Notably, the dual-treated wood exhibited lower heat release and reduced smoke emission compared with the mono-treated wood, indicating a cooperative effect between CBP and fire-retardant coatings, beneficial to the improvement of fire safety. This experimental work improved fire retardance and suppressed smoke release in flammable materials, and offers a new design for developing fire-retardant coatings.

Epoxidized soybean oil (ESO)-based thermosets are attracting increasing attention because they are derived from renewable resources. To date, unfortunately, they have not been able to replace petroleum-based epoxy resins yet due to their poor mechanical properties and unsatisfactory thermal performances. To address the drawbacks, quercetin (QC) as a biobased polyphenol-type curing agent was chosen to increase the rigidity of ESO-QC thermosets. Meanwhile, three imidazole-type accelerators, including N-methylimidazole (N-MI), 4-methylimidazole (4-MI), and biobased histidine (His), were introduced to reduce the activation energy during curing and to tailor the network structures after curing. All ESO-QC thermosets possessed excellent thermal stabilities, thanks to the high rigidity and cross-linking density, among which the initial decomposition temperature of ESO-QC/His was up to 348 °C. Due to the different topological structures of ESO-QC thermosets resulted from different catalytic mechanisms of N-MI and 4-MI, superior tensile and flexural strengths of 44.7 and 81.8 MPa were obtained in ESO-QC/4-MI thermosets, respectively, while the ESO-QC/N-MI thermosets displayed outstanding tensile modulus of 1058 MPa, which could rarely be discovered in biobased systems. In addition, the Izod unnotched impact strength of ESO-QC/His thermosets reached 23.5 kJ·m–2, which was even higher than that of the commercial petroleum-based epoxy resins. These features provide great potential for the sustainable polymers for versatile applications.

The boundaries between phthalocyanine synthesis and combustion chemistry were broken through to achieve molecular fireproofing via in situ phthalocyanine (Pcs) synthesis during combustion. Furthermore in situ Pcs chemistry achieves a flame-retarding organic thermoplastic polymer, showing state-of-the-art fire-safety performance and an ultra-low fire hazard.

As typical anisotropic materials combining the entropy elasticity of an elastomer with the self-organization of rigid mesogens, liquid crystalline elastomers (LCEs) possess the emerging application...

Upon heating, polyesters decompose to small molecules and release flammable volatiles and toxic gases, primarily through chain scission of their ester linkages, and therefore exhibit poor fire-safety properties, thus restricting their applications. Reported herein is an end-group-capturing effect of (bis)oxazoline groups, generated from the thermal rearrangement of the N-(2-hydroxyphenyl)phthalimide (HPI) moiety which was incorporated into the polyester chain by copolymerization. These copolyesters, as a result, exhibit high efficiency in retarding decomposition by capturing the decomposed products, particularly for the carbonyl-terminated fragments, thus increasing the fire-safety properties, such as self-extinguishing, anti-dripping, and inhibiting heat release and smoke production. The successful application of this method in both semi-aromatic and aliphatic polyesters provide promising perspectives to designing versatile fire-safe polymers.

To explore clinical and radiographic effects of percutaneous pie-crusting deep medial collateral ligament release in patients with posterior horn tear of medial meniscus combined with tight medial compartment.From January 2012 to December 2016, 35 patients with medial meniscus posterior horn injury were treated with percutaneous pie crusting deep medial collateral ligament release technique, including 21 males and 14 females, aged from 21 to 55 years old with an average of (39.1±6.5) years old. Degree of meniscus extrusion were recorded before and 24 months after operation. The knee valgus stress test was performed to evaluate stability of medial collateral ligament, and compared difference between healthy and affected side. Lysholm and IKDC functional scores were compared before and 24 months after operation.All patients were followed up from 27 to 60 months with an average of (36.7±6.8) months. All patients were underwent operation, the wound healed well without complications. Operative time ranged from 0.5 to 1.2 h with an average of (0.8±0.4) h. Nineteen patients were performed partial meniscectomy, 16 patients were performed repair suture. Convex of meniscus before operation was (1.5±0.7) mm, and (1.7±0.4) mm after operation;had no statistical difference(For patients with medial meniscus tear of posterior horn combined with tight medial compartment, percutaneous pie-crusting deep medial collateralligament release could improve medial compartment space, and Knee valgus instability and meniscus extrusion are not affected.

High-performance and multifunctional epoxy resins (EPs) are of great use in the booming electric & electronic and 5G fields, however their fabrication shows huge challenges. Herein, through a facile strategy by simply incorporating a functional molecule DPI (phosphaphenanthrene polyethylenimine), which possessed a unique structure with hyperbranched polyethyleneimine as flexible inner core and phosphaphenanthrene groups as rigid outer shell, a high-performance and multifunctional epoxy resin was successfully fabricated. The hyperbranched rigid-flexible structure of DPI endowed the resultant thermoset EP-DPI with superb mechanical performance and high glass transition temperature, for which, at a low DPI content (≤4 wt%), EP-DPI exhibited 160%, 40%, and 31% improvement in impact toughness, tensile strength, and flexural strength compared with neat EP. At the same time, the good compatibility between DPI and the EP matrix enabled EP-DPI to be highly transparent, and the aromatic phosphorus structure endowed EP-DPI with excellent UV-shielding effect in the UV-A band. The dielectric performance of EP-DPI was enhanced due to the unique structure of DPI and its interaction with the EP matrix. Furthermore, the phosphaphenanthrene groups endowed EP-DPI with excellent anti-ignition, self-extinguishing, and low heat release during combustion. This work opens up a new strategy for developing novel high-performance and multifunctional EPs with potential versatile applications.

To obtain a latent curing epoxy system with satisfactory thermal stability, flame retardance and dielectric properties, imidazolium dibenzo[c,e][1,2]oxaphosphate (IDOP) was synthesized by a facile way and utilized as a latent flame-retardant curing agent for epoxy resins (EP). It was confirmed that IDOP/EP one-pack system kept reactive inert near room temperature and cured efficiently under heating with a moderate heat release. The curing procedure was explored by X-ray photoelectron spectroscopy (XPS), confirming that the flame-retardant group was incorporated into epoxy chains by covalent and/or ionic bonds, hence the intrinsic flame retardance and excellent thermal stability were given to the cured resins finally. With only 15 wt% IDOP additions, the limiting oxygen index (LOI) increased to 37.0% from 20.5% of the reference sample, and UL-94 V-0 rating was achieved. The results of cone calorimetry test further certified that IDOP/EP showed satisfactory flame retardance dominating in gaseous phase, which was confirmed by the results of thermogravimetric analysis/infrared spectrometry (TG-IR). The thermal mechanical behavior of IDOP/EP was also evaluated by dynamic mechanical analysis (DMA). Especially, the incorporation of the flame-retardant group didn’t deteriorate the dielectric properties of the cured resin. Benefiting from the advances, the latent curing epoxy system with excellent comprehensive performance exhibited potential for versatile applications.

Bonding aryl groups with carbon-nitrogen double bond is a critical structural factor for the self-crosslinking of Schiff bases at high temperature. In this study, a novel aromatic Schiff base “5-(benzylidene-amino)-isophthalic acid dimethyl ester (BA)” has been designed as a self-crosslinking monomer for poly(ethylene terephthalate) (PET) based copolyesters (BAnPETs). The cross-linking behaviors, flame retardancy and non-dripping performance of BAnPETs have been investigated by simultaneous thermal analysis (TG-DSC), dynamic rheology, limiting oxygen index (LOI), UL-94 vertical burning and cone calorimetry tests. It is found that BA units can cross-link during combustion resulting in high melting viscosity and enhance char forming for BAnPETs, which endows the copolyesters with excellent flame retardancy and non-dripping behavior. Incorporating of BA with a low content (only 7.7 mol%), the LOI value of copolyester increases from 22.0% to 31.0%, and at the same time it achieves V-0 rating in the UL-94 vertical burning test. The mode action of Schiff bases on flame retardation and anti-dripping of copolyesters also has been investigated, and the results show that the aromatic Schiff base groups can lead copolyesters to form nitrogen-containing cross-linkable networks and further transform into compact char layer during combustion. The char layer which acts as an effective barrier, cuts off oxygen, hinders the volatilization of combustible gas and isolates unburned polymer from fire resource. This work suggests that using Schiff base as a self-crosslinkable monomer is a new and effective way for fire-safe polymeric materials.

The use of conventional flame-retardant elements such as Cl, Br, P for carbon-based polymers usually leads to the deterioration of smoke and toxic gas release, and possesses serious environmental and ecological issues. Herein, we proposed a facile strategy to largely improve the flame-retardant efficiency of an eco-friendly flame-retardant method. By simply tailoring the substitution position of the functional polymerization monomer, the corresponding copolymer exhibited extremely high flame retardancy, including a 59% lower peak heat release rate (pHRR), a 48% lower smoke density, a high limiting oxygen index (LOI) of 30%, and passed the UL-94 V-0 rating without dripping. More importantly, the para-substitution copolymer showed a much higher flame-retardant efficiency than the meta-substitution copolymer, for which the monomer content needed for UL-94 V-0 rating, high LOI value, and low smoke and toxic gas release largely decreased by 25%. The detailed mechanism and the different performance between the two copolymers were comprehensively investigated. The results first confirmed the “end-group-capturing” mechanism, then revealed that the different flame-retardant efficiency was owing to the different thermal rearrangement capability of the two functional monomers. The molecular-level mechanism revealed here provided a novel thinking for designing flame-retardant polymers.

Conventional methods of improving the flame retardancy of PA 6 usually involve the sacrifice of mechanical properties, which is unfavorable for the practical application. Herein, two Schiff-base containing phosphonate oligomers PSA and POSC, were designed and used as novel flame retardants for PA 6. The PA 6-PSA20 composite involving P-Ph structure achieved a LOI value of 27% and UL-94 V-0 rating, while the PA 6-POSC20 composite involving P-O-Ph structure achieved a higher LOI value of 32% but a UL-94 V-2 rating. The PA 6-POSC composites also exhibited better heat-suppression effect than the PA 6-PSA composites. The different flame-retardant mechanism of these two flame retardants were comprehensively studied via Raman spectra, XPS, FTIR, TG-IR and Py-GC/MS. Additionally, the PA 6 composites all exhibited great processability and largely retained mechanical properties. This work proposed an efficient route for preparing flame-retardant polyamide composite with excellent overall performance.

Despite the excellent overall performance, the application of polyesters is severely restricted by their inherently high flammability. Although many gratifying results have been achieved through different fire-safety methods, customization is still needed for every specific polymer, thus a generally applicable method is highly desired. Herein, we developed an eco-friendly and general fire-safety method for semi-aromatic polyesters based on the “end-group-capturing” concept. The functional monomer was chemically incorporated into the main chains of a series of semi-aromatic polyesters with similar structures (i.e., polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT)), and the specific contribution of the fire-safety method was investigated comprehensively. The results showed that the fire safety of all the copolyesters were efficiently improved, while interestingly, the fire safety gradually declined with the increase of the methylene group numbers in their molecular chains. The reason behind this phenomenon was comprehensively studied by both theoretical calculation and experiments. The increasing cyclization tendency of the copolyesters derived from the increase of the methylene group numbers was proved to be responsible for the decrease of the fire safety. The successful application and in-depth mechanism revealed here provide theoretical supports for the development of novel fire-safety polymeric materials.

Inherent flame-retardant semi-aromatic polyesters, containing special aryl ether and/or ketone structures (“Ar–CO–Ar”, “Ar–O–Ar”, “Ar–O–Ar–O–Ar” or “Ar–O–Ar–CO–Ar–O–Ar”) were synthesized successfully. Interestingly, these polyesters show different flame retardancy beyond our traditional knowledge that more benzene rings are beneficial to flame retardancy. The polyester containing “Ar–O–Ar–O–Ar” shows excellent flame retardancy, whose LOI value reaches 34.1% and the UL-94 rating is V-0. Meanwhile, the polyester with the “Ar–O–Ar–CO–Ar–O–Ar” structure does not perform expectedly well (31.6% and V-2 rating respectively). In order to make clear the effect of aryl ether and/or ketone structure units on the flame retardancy, the pyrolysis behaviours and the char residue are investigated by Py-GC/MS, TGA, and SEM. In the TGA test, the char residues of polyesters containing “Ar–CO–Ar”, “Ar–O–Ar” “Ar–O–Ar–O–Ar” or “Ar–O–Ar–CO–Ar–O–Ar” are 31.6%, 22.5%, 30.6% or 38.7%, respectively. These values do not match with the calculated results, which indicate that some special reactions occur during combustion. Furthermore, these polyesters show a common initial pyrolysis pathway and subsequent unique processes in the Py-GC/MS test. Their pyrolysis intermediate products can bind small-molecule free radicals, and eventually form different conjugated aromatic structures. In this way, inherent flame-retardant polyesters are obtained even without any traditional flame-retardant elements. And their flame retardant performance has great relationship with the amount of char formation, the microstructure of char, and the chemical structure of pyrolysis products.

The flame-retardant waterborne polyurethane (WPU) has attracted more and more attentions from academia and industry. However, the addition of conventional flame retardants into WPU will damage the emulsion stability and introduce the potential further risk to demulsification and preparation failure. In this work, a novel flame-retardant approach is proposed, demonstrating outstanding efficiency, excellent compatibility and minimized side effect. A water-soluble ionic liquid 1-methyl-3-((6-oxidodibenzo[c,e] (Akindoyo et al., 2016; Chattopadhyay and Raju, 2007) [1,2]oxaphosphinin-6-yl)methyl)-1-H-imidazol-3-ium-4-methylbenzenesulfonate ([Dmim]Tos) is applied as the additive flame retardant for the WPU dispersions. The resulting WPUs (WPU/[Dmim]Toses) display excellent flame retardancy via a low loading content (max 6.0 wt%) and potential adhesion applicable to industries, while maintaining the major comprehensive performance, including storage stability, mechanical property, thermal stability, transparency, hydrophobicity, etc. Effort from this work, besides of overcoming the explicit drawback, also serves as reference of novel methodologies to solve the compatibility issue between additive agents and WPU.

Previous approaches to suppressing fire hazards are concentrated on brominated flame retardants (BFRs) or phosphorus flame retardants (PFRs). However, their chemical hazards to health and environment have not been able to be ignored currently. It is quite urgent to propose a durable and environmentally-friendly fire-safe strategy, which can eliminate migration, release, and environmental hazards of traditional flame retardants during their use, disposal, and recycling. Herein, we design a fire-responsive molecule (FRM) only containing C, H, and O elements based on full-life-cycle consideration and achieve fire safety via the synergy of specifically binding aliphatic fragments and aromatized charring in combustion. The resulting polymer shows low fire hazard with excellent self-extinguish, low organic volatiles/heat/smoke release, and good comprehensive performance. This polymer can be fabricated to fibres with potential applications for textiles, and electronics, etc. Therefore, we achieve a durable fire-safe strategy without flame-retardant chemicals hazard. This approach can fundamentally eliminate the potential chemical hazards associated with the introduction of halogen or phosphorus flame retardants and give a new vision about solving the "flame retardant chemical hazard issues" that are debated, tracked, and evaluated for several decades.

One-pack flame-retardant epoxy resins (EP) with long pot life before using, high curing activity during operating and satisfactory fire safety after curing are extremely needed in electrical & electronics and composite industries. Here, imidazolium diphenylphosphinate (IDPP) was designed and synthesized by a facile way, thereafter used as a hardener for diglycidyl ether of bisphenol A type EP (DGEBA). IDPP/DGEBA possessed long-term stability in liquid state at ambient temperature while cured rapidly under heating, presenting controllable latent curing behavior relying on temperature. Specific phosphorus-containing groups were finally attached to epoxy chains mainly by ionic bonds, thus slightly affected the network structures of the resins. Consequently, the cured EP simultaneously achieved high glass transition temperature (Tg), good thermal stability, excellent flame retardancy and expected dielectric performance. Especially, with only 15 wt% IDPP incorporated, the cured DGEBA exhibited a high Tg (172.7 °C), low dielectric constant (4.00) and loss (0.004) at 10 MHz respectively, and easily achieved UL-94 V-0 rating with a high limiting oxygen index (37.0%). The data obtained from cone calorimetry indicated the flammability of the resins was significantly suppressed when cured with IDPP. It was verified by thermogravimetric analysis/infrared spectrometry that IDPP showed dominating vapor-phase flame-retardant effect in DGEBA systems. Additionally, IDPP was also qualified as a latent hardener for tetraglycidyl diaminodiphenylmethane (TGDDM) with excellent thermal stability and flame retardancy.

Aiming to develop high performance flame-retardant epoxy resin (EP), a novel phosphorus-containing semi-aromatic polyester named poly[4,4′-bis(6-hydroxyhexyloxy)biphenyl 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-phosphaphenanthrene-10-oxide] (PBHDDP) was synthesized and employed as a multi-functional additive for EP with simultaneously flame retardation and mechanical enhancement. Appropriate thermodynamic compatibility between PBHDDP and the EP network made no phase separation occurred in the process of curing reaction. Compared with neat EP, the resultant EP thermoset containing barely 2.5 phr (2.44 wt%) of PBHDDP exhibited superior mechanical properties with 20.3% and 149% increase in tensile and impact strengths, respectively. Simultaneously, as increasing the content of PBHDDP, flame retardancy of the thermosets enhanced obviously as evidenced by the elevated anti-ignition and self-extinguishing performance, along with the reduced combustion rate and heat release. Whereas, obvious sacrifice of either transparency, glass transition temperature or thermal stability was absent. The exploration of this novel state-of-art that simultaneously improved the mechanical properties and flame retardancy of EP thermosets at a relatively low content of a single-component multi-functional additive provided a powerful basis for the technologies and potential industrial applications.

In order to avoid potential environmental and safety problems caused by conventional flame retardants, we synthesized the flame-retardant-element-free copolyesters via chemically incorporating the structural units of bisphenol A and bisphenol F into the PET main chain via melt polymerization, respectively. The chemical structures of resulting copolyesters were confirmed by 1H NMR and 13C NMR spectroscopy. Interestingly, though there exists only a small structural difference between bisphenol A and bisphenol F, those two kinds of copolyesters show different thermal stabilities, pyrolysis behaviours and flame retardant performances. Pyrolysis-GC/MS tests were performed to investigate the pyrolysis mechanism of the copolyesters, and the results showed that the “Ar–CH2–Ar” structure units (bisphenol F) would lead to rearrangement reactions at high temperature, ultimately forming the phenanthrene ring structures; whereas “Ar–C(CH3)2−Ar” structure units (bisphenol A) could not. The corresponding specific pyrolysis processes are proposed. Thermogravimetric analysis (TGA) results indicated that these rearrangement reactions would most likely occur in the solid state of the copolyesters and made them have high residues. Cone calorimeter measurements, LOI and vertical UL-94 tests were used to characterize the flame-retardant properties of the copolyesters, and the results proved that the copolyesters containing bisphenol F had better flame retardancy, more char formation and less melt drippings than those containing bisphenol A due to the rearrangement reactions.

In order to avoid the serious melt-dripping problems caused by conventional phosphorus flame retardants, a new arylene-ether containing monomer named 2,2′-(4,4′-(1,4-phenylenebis(oxy))bis(4,1-phenylene))bis(oxy) diethanol (PBPBD) was synthesized and introduced into the PET main-chain via condensation polymerization. With the incorporation of arylene-ether units, the thermal stability and the char residue from combustion of flame-retardant-element-free copolyesters containing PBPBD (BDxPETs) increased dramatically. However, the crystallinity and melting temperature of these copolymers were lower than the same quantities for PET. Thermal degradation kinetic was investigated using the Ozawa-Flynn-Wall method, which illustrated that the apparent activation energy for decomposition of the copolyesters was enhanced with increasing the conversion and the content of PBPBD. Py-GC/MS results showed that the PBBPD structural units undergo rearrangement reactions at high temperature, and ultimately form conjugated heteroaromatic structures, which lead to the formation of stable char residues with unique “stick-shaped” micro-morphology. Due to these rearrangement reactions, BDxPETs showed an expected flame retardant performance and a reduction in smoke generation during combustion. For example, the LOI value for BD10PET was 28.4, and the total smoke production (TSP) was 10.4 m2, much smaller than that for PET, 18.8 m2. Moreover, melt-dripping was restricted.

Rationale: Medial collateral ligament (MCL) injury is a common sports injury. The damage mainly occurs in ligament fibers, but MCL avulsion fracture is extremely rare and only a few reports have been published. Patient concerns: Herein, we present a healthy 21-year-old man with an avulsion fracture of the MCL of the right knee sustained during snowboarding. Diagnosis: Clinical and radiographic findings confirmed the presence of an avulsion fracture at the proximal attachment of the MCL, combined with complete anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) rupture. Interventions: The patient underwent single-stage ACL, PCL reconstruction, and MCL repair. Outcomes: Two weeks after the surgery, the patient developed heterotopic ossification (HO) at the medial side of the knee, HO tended to be stable and mature at the 3-month follow-up examination. One year after the operation, the patient's knee was fully functional, stable, and pain free. Lessons: Femoral attachment avulsion fracture of the MCL is in contrast to common isolated MCL injuries. Early surgical repair is advocated for the greatest benefit. Orthopedic surgeons should keep the potential complication HO in mind and develop rational strategies for HO prevention and treatment.

Phosphorus-containing poly(ethylene terephthalate-co-diethylene terephthalate) (PEDT) with a low melting temperature was synthesized through esterification and copolycondensation of terephthalic acid, ethylene glycol, diethylene glycol (DEG), and 3-(hydroxyphenylphosphinyl)propionic acid (HPPPA). DSC results showed that PEDTs still were crystallizable and that the lowest melting temperature of the PEDTs was reduced to 118.0 °C although the chain regularity was destroyed by the incorporation of comonomers. It was found that the addition of HPPPA can improve the thermal oxidative stability of copolyesters. The results of the limiting oxygen index (LOI) test, the UL-94 vertical test, and the cone calorimeter test indicated that HPPPA endowed PEDT with good flame-retardant properties. The LOI values of the PEDTs were increased to 30.5–34.8, the UL-94 ratings of vertical burning were improved to V-0, and both the peak heat release rate (pHRR) and the total heat release (THR) obviously decreased.

This manuscript reports a new method to solve the conflict between the flame retardance and anti-dripping of poly(ethylene terephthalate) by introducing azobenzene groups into the main-chain. This novel polyester containing azobenzene units in the main chain (PEAT) was synthesized via esterification and copolycondensation of terephthalic acid, ethylene glycol and azobenzene-4,4′-dicarboxylic acid. TG-DSC, rheological and UV-Vis results proved the occurrence of the thermal and chemical crosslinking reaction by adjacent azobenzene groups. In the TG test, the residue and thermooxidative stability were obviously increased by the high-temperature crosslinking of the azobenzene groups. The cone calorimetric analysis and LOI tests further confirmed the self-extinguishing properties and inhibition of melt-dripping. Elemental analysis results indicated that besides partial decomposition of azobenzene groups into N2, most nitrogen was retained in the residue after high-temperature crosslinking. Besides, the char became more compact with an increase of azobenzene-4,4′-dicarboxylic acid. All the results demonstrated that through the high-temperature crosslinking of the azobenzene group, PEAT exhibited a good balance between flame retardance and anti-dripping properties.