The incorporation and release of ungeremine,an antifungal Amaryllidaceae alkaloid,in poly(lactic acid)/poly(ethylene glycol) nanofibers

Ungeremine (UNG) is an alkaloid typically isolated from Pancratium maritimum or synthesized by the oxidation of lycorine. This antifungal alkaloid was incorporated into electrospun nanofibers based on blends of poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG). The effect of the UNG on the structure, morphology, and thermal properties of the fibers was evaluated, and the release of the alkaloid from the fibers was quantified. Studies on the release of the UNG for the nanofibers show that the release rate is related to the amount and distribution of the PEG in the nanofiber matrix. Initial burst release of the antifungal alkaloid is related to the PEG in the nanofibers, where after a sustained release occurs indicating that the UNG is present in both the PLA and PEG domains in the nanofibers.     

Intercalated clay structures and amorphous behavior of solution cast and melt pressed poly(ethylene oxide)–clay nanocomposites

The polymer nanocomposite (PNC) films consisted of poly(ethylene oxide) (PEO) and sodium cations montmorillonite (MMT) clay were prepared by aqueous solution casting and direct melt press compounding techniques, whereas the films of PEO with trimethyl octadecyl ammonium cations organo‐modified montmorillonite (OMMT) clay were formed by melt pressed technique. The clay concentrations in the nanocomposites used are 1, 2, 3, 5, 10, and 20 wt % of the PEO weight. The X‐ray diffraction patterns of these nanocomposites were measured in the angular range (2θ) of 3.8–30°. The values of basal spacing d₀₀₁ of MMT/OMMT, clay gallery width W_cg, d‐spacings of PEO crystal reflections d₁₂₀ and d₁₁₂, and their corresponding crystallite size L, and the peaks intensity I (counts) were determined for these nanocomposites. Results reveal that the nanocomposites have intercalated clay structures and the amount of intercalation increases with the increase of clay concentration. As compared to melt pressed PEO–MMT nanocomposites, the amount of clay intercalation is higher in aqueous solution cast nanocomposites. At 20 wt % MMT dispersion in PEO matrix, the solution cast PEO–MMT nanocomposite almost changes into amorphous phase. The melt press compounded PEO–OMMT films show more intercalation as compared to the PEO–MMT nanocomposites prepared by same technique. In melt pressed nanocomposites, the PEO crystalline phase significantly reduces when clay concentration exceeds 3 wt %, which is evidenced by the decrease in relative intensity of PEO principal crystalline peaks. The effect of interactions between the functional group (ethylene oxide) of PEO and layered sheets of clay on both the main crystalline peaks of PEO was separately analyzed using their XRD parameters in relation to structural conformations of these nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39898.     

Isothermal crystallization kinetics of poly(lactic acid)/synthetic mica nanocomposites

The isothermal crystallization kinetics of PLA/fluoromica nanocomposites was studied. Three types of synthetic mica at three concentrations (2.5, 5.0, and 7.5 wt % mica) were used and the effect of these micas on the crystallization and thermal properties of PLA was investigated by differential scanning calorimetry (DSC). The Avrami and Hoffman‐Weeks equations were used to describe the isothermal crystallization kinetics and melting behavior. Addition of these micas to the PLA matrix increased the crystallization rate, and this effect depended on the mica type and concentration. While the nonmodified Somasif ME‐100 exerted the smallest effect, the effect observed for the organically modified Somasif MPE was the most pronounced. The lower half‐time of crystallization t_1/2 was around 3 min for the PLA/Somasif MPE nanocomposites containing 7.5 wt % of filler at 90°C, which is about 16 min below that found for neat PLA. The equilibrium melting temperature ( ) of PLA were estimated for these systems, showing an increase in the composites and an increase with increasing loading, except for PLA/Somasif MPE, in which the increase of the mica content decreased about 5°C. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40322.     

Photo‐induced protonation and conductivity of polyaniline/poly(ethylene glycol) and polyaniline/[poly(ethylene glycol)‐grafted polyaniline] composites

Composites of polyaniline in its emeraldine base form (PANI‐EB) and photo‐acid generators (PAG) show an increase in conductivity upon photo‐irradiation due to the protonation of PANI‐EB. Such materials may be utilized to fabricate conducting patterns by photo‐irradiation. However, the conductivity obtained by direct irradiation of PANI‐EB/PAG composites was normally quite low (<10^?3 S/cm) due to aggregation of highly loaded PAG. In this work, poly(ethylene glycol) (PEG), which is a proton transfer polymer, was added to PANI‐EB/PAG. Results showed that addition of low M_w (550) PEG significantly enhance the photo‐induced conductivity. Conductivities as high as 10^?1–10⁰ S/cm were observed after photo‐irradiation. This conductivity is comparable to that of PANI‐salt synthesized by oxidizing aniline in the presence of an acid. High M_w (8000) PEG is much less effective than PEG 550, which is attributed to its lower compatibility with PANI. PEG‐grafted PANI (N‐PEG‐PANI) was also studied as an additive. Composites of PANI‐EB and N‐PEG‐PANI showed conductivity as high as 10² S/cm after treatment with HCl vapor. The photo‐induced conductivity of the N‐PEG‐PANI/PANI‐EB/PAG composite reached 10^?2–10^?1 S/cm. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Study on the properties of polyethylene/montmorillonite nanocomposites prepared by a novel vane mixer

A novel mixer‐vane mixer which is based on elongation flow was used to prepare high‐density polyethylene (HDPE)/montmorillonite (MMT) nanocomposites without any additives. The effect of elongation flow on MMT intercalating in HDPE matrix was studied in terms of rotor speed and mixing time. X‐ray diffraction and transmission electron microscope analyses showed that exfoliated and intercalated nanostructures were obtained when the rotor speed was 40 and 50 rpm, and mixing time was 6 minutes. For all samples prepared by vane mixer, MMT layers showed fine intercalation in the nanocomposites. Differential scanning calorimetry and thermogravimetric analysis were used to study the thermal properties of the nanocomposites. The results showed that the addition of MMT can improve the crystallization of the HDPE. Tensile test revealed the relationships between the mechanical properties and process parameters. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42600.     

The effect of poly(ethylene glycol) as plasticizer in blends of poly(lactic acid) and poly(butylene succinate)

The effect of polyethylene glycol (PEG) on the mechanical and thermal properties of poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) blends was examined. Overall, it was found that PEG acted as an effective plasticizer for the PLA phase in these microphase‐separated blends, increasing the elongation at break in all blends and decreasing the T_g of the PLA phase. Significant effects on other properties were also observed. The tensile strength and Young's modulus both decreased with increasing PEG content in the blends. In contrast, the elongation at break increased with the addition of PEG, suggesting that PEG acted as a plasticizer in the polymer blends. Scanning electron microscope images showed that the fracture mode of PLA changed from brittle to ductile with the addition of PEG in the polymer blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43044.     

Shape‐memory behaviors of electrospun chitosan/poly(ethylene oxide) composite nanofibrous membranes

With aim of constructing a class of functional environmentally friendly materials, we electrospun chitosan (CS) blends with various contents of poly(ethylene oxide) (PEO) into a series of composite nanofibrous membranes exhibiting shape‐memory behaviors. In the present composite system, CS and PEO served as hard and soft domains, respectively. The CS, presenting no thermal transition, and the PEO, with apparent melting–crystallization, were demonstrated by differential scanning calorimetry testing. Characterizations also revealed that the morphologies of the CS/PEO membranes were controlled by the mass ratios of CS/PEO. The composite fibrous membranes showed great mechanical performances and thermal stabilities as well. Moreover, CS/PEO possessed excellent shape‐memory behaviors. Such fibrous membranes could complete their shape‐recovery processes within 20 s at the temperature of 20°C above the melting transition temperature (T_m). Both the shape fixity and shape‐recovery ratios were higher than 90%, even after five cycles. The CS/PEO fibrous membranes present significant potential applications in the field of biotechnology and tissue engineering, such as in scaffolds and smart tubes. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42532.     

Nanocomposites of poly(3‐hydroxybutyrate)/organomodified montmorillonite: Effect of the nanofiller on the polymer's biodegradation

Poly(3‐hydroxybutyrate) (PHB) is a biopolymer that can be degraded by extracellular PHB depolymerase. This enzyme is secreted by various microorganisms, but bacterial PHB depolymerases are the most widely studied. The biodegradability rate depends on various factors. By controlling them, the biodegradability rate can change and be customized, and thus, the applications of the polymer can increase and become more diverse. In this work, the role of organomodified montmorillonite (OMMT) on PHB biodegradation was investigated. Using the melt‐mixing method, nanocomposites of PHB and OMMT as the nanofiller were prepared. The enzyme was isolated from the fungus Penicillium pinophilum and the enzymatic degradation was studied for both pure polymer and its nanocomposites. It was found that, after 25 days of enzymatic degradation, the mass loss was very low, while the polymer's average molecular weight as measured by gel permeation chromatography was significantly reduced (more than 50%). Additional peaks corresponding to PHB oligomers (from pentamers to nonamers) appeared after biodegradation. This behavior was observed for pure PHB and the hybrid materials. Scanning electron microscopy imaging of the biodegraded surfaces and analysis of these images showed that the higher amount of nanoclay (10 wt %) resulted in larger biodegraded area of the specimens. The results presented here demonstrate that the presence of the nanoclays enhances the biodegradation rate of pure PHB polymer and provide quantitative data for the biodegradation of PHB/organoclay hybrid materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41656.     

Tough hyperbranched epoxy/poly(amido‐amine) modified bentonite thermosetting nanocomposites

A tough and highly flexible hyperbranched epoxy and poly(amido‐amine) modified bentonite based thermosetting nanocomposite was demonstrated. The FTIR, XRD, and TGA analyses confirmed the modification of bentonite. The formation of partially exfoliated structure of the nanocomposite with good physicochemical interactions among the hyperbranched epoxy, poly(amido‐amine) hardener and modified clay was investigated by the FTIR, XRD, SEM, and TEM analyses. Significant improvements of 750% toughness, 300% elongation at break, 50% tensile strength, 300% modulus, and 250% adhesive strength of the pristine epoxy were achieved by the formation of nanocomposites with 3 wt % of modified clay. The experimental modulus values of the nanocomposites were compared with three theoretical models to account the interactions between filler and matrix. Thus, the studied epoxy nanocomposite has great potential to be used as an advanced epoxy thermoset. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40327.     

Crystalline structure and mechanical properties of poly(ethylene terephthalate) filament embedded with nanosize clay particles

The properties of poly(ethylene terephthalate) (PET) filaments embedded with nanosize clay powder were evaluated. The moisture management function and thermal properties of the textile were found to be improved; however, the strength of the filament was lowered with a little increase in elongation. In situ analysis of the crystalline structure with small‐angle X‐ray scattering and wide‐angle X‐ray diffraction during the tensile testing showed an unstable change in intensities during the elongation. This phenomenon is related to the earlier rearrangement and breaks down the microstructure in local regions with an increase in strain. This is expected to be due to the low adhesion strength between the matrix and the embedded nanosize clay particles. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46321.     

Structural characterization of hydrophilic polymer blends/montmorillonite clay nanocomposites

The nanocomposite films comprising polymer blends of poly(vinyl alcohol) (PVA), poly(vinyl pyrrolidone) (PVP), poly(ethylene oxide) (PEO), and poly(ethylene glycol) (PEG) with montmorillonite (MMT) clay as nanofiller were prepared by aqueous solution casting method. The X‐ray diffraction studies of the PVA–x wt % MMT, (PVA–PVP)–x wt % MMT, (PVA–PEO)–x wt % MMT and (PVA–PEG)–x wt % MMT nanocomposites containing MMT concentrations x = 1, 2, 3, 5 and 10 wt % of the polymer weight were carried out in the angular range (2θ) of 3.8–30°. The values of MMT basal spacing d₀₀₁, expansion of clay gallery width W_cg, d‐spacing of polymer spherulite, crystallite size L and diffraction peak intensity I were determined for these nanocomposites. The values of structural parameters reveal that the linear chain PEO and PEG in the PVA blend based nanocomposites promote the amount of MMT intercalated structures, and these structures are found relatively higher for the (PVA–PEO)–x wt % MMT nanocomposites. It is observed that the presence of bulky ester‐side group in PVP backbone restricts its intercalation, whereas the adsorption behavior of PVP on the MMT nanosheets mainly results the MMT exfoliated structures in the (PVA–PVP)–x wt % MMT nanocomposites. The crystallinities of the PEO and PEG were found low due to their blending with PVA, which further decreased anomalously with the increase of MMT concentration in the nanocomposites. The decrease of polymer crystalline phase of these materials confirmed their suitability in preparation of novel solid polymer nanocomposite electrolytes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40617.     

Properties of poly(ethylene glycol)‐based bioelastomers

In this article, a series of poly(ether ester) bioelastomers, poly(PEG‐co‐CA)s (PECs), were synthesized by the melt polycondensation of citric acid (CA) and poly(ethylene glycol) (PEG) with molecular weights of 150, 200, 300, and 400. The measurements of the mechanical properties of the PEC series testified that these polymers were elastomers with a low hardness and high elongation, and the hydrolytic degradation of polymer films in a buffer of pH 7.4 at 37°C showed that the PECs had excellent degradability. The molecular weight of PEG had a strong influence on the degradation rates, water absorption rates, and mechanical performance of the PECs. The materials are expected to be useful for pressure hemostasis implementation in lacuna and other biomedical applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Soundproofing properties of polypropylene/clay/carbon nanotube nanocomposites

In this article, polypropylene (PP)/clay/carbon nanotube (CNT) composites were prepared via a solution blending method. Sound transmission loss (STL), determined with an impedance tube, was used to characterize their soundproofing properties. The STL for the PP/4.8 wt % clay/0.5 wt % CNT composite was about 15–21 dB higher than that for pure PP at high frequencies (3200–6400 Hz) and about 8–14 dB higher at low frequencies (580–620 Hz). X‐ray diffraction (XRD) and transmission electron microscopy (TEM) were used to study the crystallinity and the microstructure. A synergistic effect on the STL was established between the structure of the homogeneous dispersion and strong interfacial adhesion. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of interfacial pretreatment on the properties of montmorillonite/poly(vinyl alcohol) nanocomposites

This work explores the factors that control the dispersion of exfoliated montmorillonite (MMT) in poly(vinyl alcohol) (PVOH) during solution blending and solvent evaporation. Nanocomposite films were prepared by solution blending of aqueous PVOH solutions with dilute suspensions of fully exfoliated MMT platelets (as confirmed by AFM). Dynamic light scattering (DLS) indicates that addition of MMT suspensions to PVOH solutions results in undesired particle aggregation and thus poor MMT dispersion in cast films (as evidenced by transmission electron microscopic images and gas permeation measurements). We believe that PVOH bridging induces MMT platelet aggregation. To counteract bridging aggregation, we explore the novel idea of pretreating the MMT surface with a small amount of compatible polymer prior to solution blending with PVOH. We hypothesize that “pretreating” the MMT platelet surfaces with adsorbed polymer in dilute suspensions will protect the platelets from bridging aggregation during solution blending and solvent evaporation. MMT/PVOH composite films have been prepared using low‐molecular‐weight PVOH as the pretreatment polymer; and low‐, medium‐, and high‐molecular‐weight PVOH as the matrix polymer. A PEO‐PPO‐PEO triblock copolymer (F108 from the Pluronics^® family) was also evaluated as the pretreatment polymer. DLS shows that pretreated MMT platelets are less susceptible to aggregation during blending with PVOH solutions. Results compare the crystalline structure, thermal properties, dynamic mechanical properties, gas permeability, and dissolution behavior of MMT/PVOH films incorporating untreated versus pretreated MMT. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41867.     

Porous poly(L‐lactic acid)/poly(ethylene glycol) blend films

Poly(L ‐lactic acid) (PLLA: M_w = 19.4 × 10⁴)/poly(ethylene glycol) (PEG: M_w = 400) blend films were formed by use of a solvent‐cast technique. The properties and structures of these blend films were investigated. The Young's modulus of the PLLA decreased from 1220 to 417 MPa with the addition of PEG 5 wt %, but the elongation at break increased from 19 to 126%. The melting point of PLLA linearly decreased with increases in the PEG content (i.e., pure PLLA: 172.5°C, PLLA/PEG = 60/40 wt %: 159.6°C). The PEG 20 wt % blend film had a porous structure. The pore diameter was 3–5 μm. The alkali hydrolysis rate of this blend film was accelerated due to its porous structure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 965–970, 2004     

Nanofibrous nonwovens based on dendritic‐linear‐dendritic poly(ethylene glycol) hybrids

Dendritic‐linear‐dendritic (DLD) hybrids are highly functional materials combining the properties of linear and dendritic polymers. Attempts to electrospin DLD polymers composed of hyperbranched dendritic blocks of 2,2‐bis(hydroxymethyl) propionic acid on a linear poly(ethylene glycol) core proved unsuccessful. Nevertheless, when these DLD hybrids were blended with an array of different biodegradable polymers as entanglement enhancers, nanofibrous nonwovens were successfully prepared by electrospinning. The pseudogeneration degree of the DLDs, the nature of the co‐electrospun polymer and the solvent systems used for the preparation of the electrospinning solutions exerted a significant effect on the diameter and morphology of the electrospun fibers. It is worth‐noting that aqueous solutions of the DLD polymers and only 1% (w/v) poly(ethylene oxide) resulted in the production of smoother and thinner nanofibers. Such dendritic nanofibrous scaffolds can be promising materials for biomedical applications due to their biocompatibility, biodegradability, multifunctionality, and advanced structural architecture. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45949.     

Polymer electrolytes based on poly(ethylene glycol) and cyanoresin

Polymer electrolytes based on a mixed polymer matrix consisting of poly(ethylene glycol) (PEG) and cyanoresins with lithium salt and plasticizer were prepared with an in situ blending process to improve both the mechanical properties and the ionic conductivity (σ). The PEG/lithium perchlorate (LiClO₄) complexes, including blends of cyanoethyl pullulan (CRS) and cyanoethyl poly(vinyl alcohol) (CRV), exhibited higher σ's than a simple PEG/LiClO₄ complex when the blend compositions of CRS/CRV were 5 : 5 or 3 : 7 or than CRV alone. When the CRS/CRV blend was compared with a copolymer of cyanoethyl pullulan and cyanoethyl poly(vinyl alcohol) (CRM) in the same molar ratio, the σ values of the polymer electrolytes containing the CRM copolymer series were slightly higher than those of the CRS/CRV blends containing PEG/LiClO₄ complexes. Moreover, the addition of cyanoresin to PEG/LiClO₄/(ethylene carbonate–propylene carbonate) polymer electrolytes provided better thermal stability and dynamic mechanical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2402–2408, 2007     

Decomposition of poly(ethylene glycol) in nanocomposites

Poly(ethylene glycol) (PEG) has been widely used in studies of polymer–clay nanocomposites because it readily intercalates in smectite clays. Nanocomposites were formed from PEG with molecular weights (M_w) ranging from 300 to 20,000, as evidenced by expansion of the basal planar spacing of the clay (d₀₀₁) in X‐ray diffraction. However PEG with high molecular weight (≥ 10,000) readily underwent degradation during preparation of composites when heated at low temperature (60°C) due to oxidative attack. Molecular weight distribution determined by gel permeation chromatography showed that this degradation always happened with or without the presence of clay and it became more serious when the molecular weight was higher. The reduction in pH of aqueous PEG solutions after degradation increased with molecular weight. Since d₀₀₁ was independent of molecular weight over a wide range, such degradation cannot be detected by this method. Precautions against oxidative attack are therefore recommended to avoid decomposition when preparing PEG–clay nanocomposites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 548–552, 2004     

Syntheses of poly(lactic acid)‐poly(ethylene glycol) serial biodegradable polymer materials via direct melt polycondensation and their characterization

Directly starting from lactic acid (LA) and poly(ethylene glycol) (PEG), biodegradable material polylactic acid‐polyethylene glycol (PLEG) was synthesized via melt copolycondensation. The optimal synthetic conditions, including prepolymerization method, catalyst kinds and quantity, copolymerization temperature and time, LA stereochemical configuration, feed weight ratio m_LA/m_PEG and M_n of PEG, were all discussed in detail. When D ,L ‐LA and PEG (M_n = 1000 Da) prepolymerized together as feed weight ratio m_{D ,l‐LA}/m_PEG = 90/10, 15 h copolycondensation under 165°C and 70 Pa, and 0.5 wt % SnO as catalyst, gave D ,L ‐PLEG1000 with the highest [η] of 0.40 dL/g, and the corresponding MW was 41,700 Da. Using L ‐LA instead of D ,L ‐LA, 10 h polymerization under 165°C and 70 Pa, and 0.5 wt % SnO as catalyst, gave L ‐PLEG1000 with the highest [η] of 0.21 dL/g and MW of 15,600 Da. Serial D ,L ‐PLEG with different feed weight ratio and M_n of PEG were synthesized via the simple and practical direct melt copolycondensation, and characterized with FTIR, ¹H NMR, GPC, DSC, XRD, and contact angle testing. D ,L ‐PELG not only had higher MW than PDLLA, PLLA and L ‐PELG, but also better hydrophilicity than PDLLA. The novel one‐step method could be an alternative route to the synthesis of hydrophilic drug delivery carrier PLEG instead of the traditional two‐step method using lactide as intermediate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 577–587, 2006     

Selective etching of polylactic acid in poly(styrene)‐block‐poly(d,l)lactide diblock copolymer for nanoscale patterning

Self‐assembled thin films of a lamellar forming polystyrene‐block‐poly(d,l )lactide (PS‐b‐PLA) block copolymer (BCP) contain a “reactive” block that can be readily removed to provide a template for substrate pattern formation. Various methods of PLA removal were studied here with a view to develop the system as an on‐chip etch mask for substrate patterning. Solvo‐microwave annealing was used to induce microphase separation in PS‐b‐PLA BCP with a periodicity of 34 nm (L_o) on silicon and silicon on insulator (SOI) substrates. Wet etches based on alkaline and enzymatic solutions were studied in depth. Fourier transform‐infrared (FT‐IR) analysis showed that basic hydrolysis using sodium hydroxide (NaOH) or ammonium hydroxide (NH₄OH) solutions resulted in greater PLA removal in comparison to an enzymatic approach using Proteinase K in a Tris‐HCl buffer solution. However, in the enzymatic approach, the characteristic self‐assembled fingerprint patterns were retained with less damage. Comparison to a dry etch procedure using a reactive ion etch (RIE) technique was made. A detailed study of the etch rate of PS and PLA homopolymer and PS‐b‐PLA shows depending on DC bias, the etch selectivity of PLA and PS can be almost doubled from 1.7 at DC bias 145 V to 3 at DC bias 270 V. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40798. Together with Krebs et al., J. Appl. Polym. Sci. (2014) 131 , 40795, doi: 10.1002/app.40795 , this article is part of a Special Issue on Polymers for Microelectronics. The remaining articles appear in J. Appl. Polym. Sci. (2014) volume 131 , issue 24. This note was added on 1st July 2014.