Prediction of clogging time during electrospinning of zein solution: Scaling analysis and experimental verification

Clogging is a critical but common problem experienced during electrospinning, especially when a high-volatility solvent is used to prepare a polymer solution. An ability to mathematically predict the time at which clogging starts to occur is thus of great importance. However, existing mathematical models could not predict the clogging time well since solvent evaporation is almost always neglected in those models. In this study, onset of clogging of a model biopolymer, i.e., zein in ethanol, was predicted through the use of a model developed based on scaling analysis; the effect of solvent evaporation is also included in the model. Experiments were also conducted to verify the predictability of the developed model. It was found that the predicted clogging time agreed well with the experimental results.     

Effect of glycerol on solution properties governing morphology,glass transition temperature,and tensile properties of electrospun zein film

An attempt was made to improve the tensile strength and elongation of electrospun zein film by addition of a plasticizer, namely, glycerol to the film forming solution. A surfactant viz. Tween®40 and NaCl were also added into the film solution to facilitate the electrospinning process. The effect of glycerol content on selected zein solution properties, i.e., surface tension, electrical conductivity, and viscosity, which in turn affect the mechanical property, morphology, and glass transition temperature (T_g) of the film were investigated. Morphology of the electrospun film was examined via scanning electron microscopy (SEM), whereas the film component was characterized by Fourier transform infrared (FTIR) spectroscopy. It was observed that as the glycerol content increased, the diameter of the electrospun fiber increased as a result of decreasing electrical conductivity with increasing surface tension of the solution. The flow‐behavior index of the solution indicated that glycerol had a significant impact on the solution flow property, hence improved fiber diameter uniformity. Besides, the tensile strength and elongation of the film were improved as glycerol content increased, but the reverse was noted at 10 wt %. T_g of the zein film decreased as the glycerol content increased. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fabrication,Gastromucoadhesivity, Swelling,and Degradation of Zein–Chitosan Composite Ultrafine Fibers

Fabrication, via electrospinning, and characterization of an ultrafine structure architected from a blend of hydrophobic zein and hydrophilic chitosan (CS) were conducted. Poly(ethylene oxide) (PEO) and nonionic surfactant, namely, Tween^® 40, were employed to improve the electrospinnability of the blend, while ethanol was used as a solvent for zein. The effects of ethanol (EtOH) concentration (85% and 90%) and ratio of zein/PEO/CS (95/2.5/2.5 and 87.5/10/2.5) on the fiber morphology as well as gastromucoadhesivity against porcine stomach mucosa were then investigated; polymer‐mucosa adhesion was also investigated via Fourier‐transform infrared spectroscopy. Swelling and degradation of the composite ultrafine fibers were investigated under 2 simulated gastric conditions, namely, at pH 2 without pepsin and at pH 1.2 with pepsin. Using 85% EtOH as a solvent for zein resulted in a spider‐web‐like morphology; the maximum detachment force (MDF), which is an indirect indicator of the gastromucoadhesivity was nevertheless higher. Zein‐based ultrafine fibers exhibited higher MDF than the zein‐PEO‐CS composite; however, the cohesiveness of the composite fibers was higher. FTIR spectroscopic results indicated molecular interactions between the composite fibers and mucin functional groups. Swelling of the composite ultrafine fibers in simulated gastric fluid (SGF) at pH 2 without pepsin was not different from that in SGF at pH 1.2 with pepsin. Nevertheless, degradation of the composite fibers in SGF at pH 2 without pepsin was much less than that in SGF at pH 1.2 with pepsin; only 20% degradation was noted in the former case.     

Electrospinning of food-grade nanofibers from cellulose acetate and egg albumen blends

Edible nanofibrous thin films were fabricated for the first time from blend solutions of cellulose acetate (CA) in 85% acetic acid and egg albumen (EA) in 50% formic acid by electrospinning. The mass percentage ratios of CA–EA in the mixed solvents varied from 100:0 to 91:9, 77:23, 66:34 and 0:100. Effects of the blend ratios on the solution properties and morphology of the resulting electrospun products were studied. The results showed that EA lacked sufficient entanglement and also possessed very high surface tension, thereby being unable to form nanofibers. The addition of CA and surfactant (Tween40®) decreased both the electrical conductivity and the surface tension of the blends (p < 0.05), which facilitated the formation of CA–EA blend nanofibers. Scanning electron microscopic images showed that the continuity of the blend fibers was improved with an increase in the EA ratio. Fourier-transformed infrared spectroscopy and thermo-gravimetric analysis results indicated that the obtained fibers were composed of both CA and EA constituents. This study demonstrated a potential to fabricate edible nanofibers from natural food biopolymers using the electrospinning technique. Due to the properties of EA, these nanofibers could provide new functionalities with respect to in vivo-controlled release of nutraceuticals and drugs.     

Coaxial electrospinning and release characteristics of cellulose acetate–gelatin blend encapsulating a model drug

In order to minimize the degradation of encapsulated compounds in the harsh environment of release medium and to minimize bursting release, a model drug was encapsulated in a kernel of ultrafine cellulose acetate (CA) and gelatin (GL) blend fibers via coaxial electrospinning. The effects of the GL ratio on the properties of the shell solution were investigated, along with the core‐to‐shell ratio. Transmission electron microscopy images showed that core–shell coaxial fibers were fabricated successfully. Scanning electron microscopy images showed that the average diameter of the fibers was 913 ± 180 nm. As the GL ratio was increased, the viscosity of the shell solution decreased. In addition, more pronounced shear thinning occurred, which resulted in coaxial fibers with thinner shells. Release characteristics of the encapsulated amoxicillin in pepsin‐containing simulated gastric fluid (SGF) with a pH of 1.2 were also investigated. It showed that the release of amoxicillin occurs owing to Fickian diffusion mechanism, with the release half‐time being approximately 5 h. Bursting release was not observed, and fibers exposed to the SGF remained intact even after 24 h. These core–shell fibers should be suitable for applications requiring the sustained release of compounds in the gastrointestinal tract. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40166.     

Effect of crosslinking reagents and hydroxypropylation levels on dual-modified sago starch properties

Chemical modification is usually carried out to overcome the unstable properties of native sago starch and improve its physical properties during processing. In this study, dual-modification of sago starch was carried out. The first stage of modification was hydroxypropylation, using propylene oxide at levels ranging from 6 to 12%. This was followed by crosslinking, using three different types of crosslinking agents: a mixture of sodium trimetaphosphate (STMP) and sodium tripolyphosphate (STPP), phosphorus oxychloride and epichlorohydrin. Through hydroxypropylation, it was found that there was a significant increase in molar substitution which in turn induces an increase in crosslinking and this was seen from the marked increase in phosphorus content and degree of substitution. This was accompanied by a significant decrease in paste clarity, swelling power and solubility compared to that of the native starch. Starch that was hydroxypropylated with 10–12% propylene oxide and crosslinked by a mixture of 2% STMP and 5% STPP produced modified starch with the most desirable properties in that it exhibited no viscosity breakdown, high acid resistance, high freeze-thaw stability and improved gel texture.     

Isolation and screening of lactic acid bacteria from Thai traditional fermented fish (Plasom) and production of Plasom from selected strains

Lactic acid bacteria (LAB) were isolated from traditional Thai fermented fish, Plasom at various fermentation periods. It was found that 138 isolates exhibited a clear zone and growth on MRS agar supplemented with CaCO_3; however, only 133 isolates were identified as LAB. Only 14 strains showed excellent inhibition zone diameters on agar when Salmonella sp. was used as an indicator for preliminary detection of antagonistic activity. Staphylococcus aureus was used for secondary screening for antagonistic activity of these 14 strains. It was found that only 7 strains exhibited good inhibition zone diameters on agar, and all of them could inhibit E. coli as the third indicator. The strains which exhibited widest zones of inhibition against Escherichia coli, S. aureus and Salmonella sp. were LPS04, LPS17, and LD219 and LPS18 respectively. Tested pathogenic strains were inhibited by 4 selected LAB. The strain which showed the best lactic acid production and pH reduction ability was LD219. Using 16s rDNA sequence analysis, LD219 was identified as Streptococcus salivarius, LPS04, LPS17 and LPS18 were identified as Enterococcus faecalis. Plasom was produced by using a mixed culture (LD219, LPS04, LPS17 and LPS18) as a starter culture compared with spontaneous and back-slopping processes. Significant differences (p < 0.05) in pH, its titratable acidity as lactic acid and number of total viable counts (TVC), LAB and Enterobacteriaceae were found in these Plasom at 0 and 8 days. However, no significant difference (p > 0.05) was observed in terms of colour, smell, taste, sour, texture and overall acceptance of Plasom produced by non-starter cultured, back-slopping and starter cultured processes.     

Investigation and prevention of clogging during electrospinning of zein solution

Electrospinning is the only known technique for fabrication of long non‐woven ultrafine‐fibers. However, a number of limitations, including low productivity and clogging of a spinneret, substantially paralyses industrial scale up of the process. Clogging is indeed an unavoidable phenomenon during electrospinning of biopolymers and the exact reason for clogging is still unclear. The aim of the present study was thus to investigate the clogging phenomenon via the study of a solution of zein/ethanol, which was used as a model biopolymer system. The gel‐like substance causing clogging at the spinneret was collected and its infrared spectrum and rheological properties were determined via Fourier transform infrared (FTIR) spectrophotometry and rheometry, respectively. The results indicated that clogging was due to solvent evaporation, which led to formation of a highly viscous semi‐solid at the spinneret. Moreover, the results also revealed that the applied voltage and polymer concentration were the key parameters affecting clogging. A means to help avoid clogging and hence an ability to continuously perform electrospinning was also proposed and tested. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010