Simple Non-Equilibrium Atmospheric Plasma Post-Treatment Strategy for Surface Coating of Digital Light Processed 3D-Printed Vanillin-Based Schiff-Base Thermosets.

A simple non-equilibrium atmospheric plasma post-treatment strategy was developed for the surface coating of three-dimensional (3D) structures produced by digital light processing 3D printing. The influence of non-equilibrium atmospheric plasma on the chemical and physical properties of vanillin-derived Schiff-base thermosets and the dip-coating process was investigated and compared to the influence of traditional post-treatment with UV-light. As a comparison, thermosets without post-treatment were also subjected to the coating procedure. The results document that UV post-treatment can induce the completion of the curing of the printed thermosets if complete curing is not reached during printing. Conversely, the plasma post-treatment does not contribute to the curing of the thermoset but causes some opening of the imine bonds and the regeneration of aldehyde functions. As a consequence, no great differences are observed between the not post-treated and plasma post-treated samples in terms of mechanical, thermal, and solvent-resistant properties. In contrast to the UV post-treatment, the plasma post-treatment of the thermosets induces a noticeable increase of the thermoset hydrophilicity ascribed to the reformation of amines on the thermoset surface. The successful coating process and the greatest uniformity of the lignosulfonate coating on the surface of plasma post-treated samples are considered to be due to the presence of these amines and aldehydes. The investigation of the UV shielding properties and antioxidant activities documents the increase of both properties with the increasing amount and uniformity of the formed coating. Interestingly, evident antioxidant properties are also shown by the noncoated thermosets, which are deduced to their chemical structures.

Role of silk nanocrystal (SNC)-ZnO as an antibacterial nucleating nanohybrid for a patterned mimic poly(lactic acid) based nanofabric.

This new investigation deals with the synthesis of an organic-inorganic nanohybrid using SNC with magnificent flower bud-shaped ZnO, termed SNC-ZnO by precipitation method. The nanohybrid (with concentrations 1 wt%, 3 wt%, and 5 wt%) was in situ incorporated into the PLA matrix to prepare the electrospun solution. The functionalized PLA composite nanofibres produced by electrospinning with SNC-ZnO nanohybrid were systematically studied using different structural and morphological analyses to meet the challenging processing requirements. The FESEM analysis gives an average diameter of nanofibres 246 ± 10.2 nm where nanohybrid tends to adhere on the surface of the PLA nanofabric increasing hydrophobicity up to water contact angle 135.3 ± 0.25 °C with 5 wt% nanohybrid incorporation. The nanofabric has significant antibacterial activity against E.Coli and S.Aureus bacteria. Further, an extensive study has been made on thermally stipulated processes using DSC on non-isothermal crystallization kinetics using different models: Avrami, Ozawa, Mo, and Tobin. The results revealed sites for heterogeneous nucleation and improvement in crystallinity, t1/2, and nucleation effects due to the incorporation of crystalline nanohybrid in PLA nanofibres. Further, the Avrami plot has confirmed both primary and secondary crystallization processes thereby considering its potential to utilize functionalized PLA nanofabric for applications in protective textile.

Structural evolution of in situ polymerized poly(L-lactic acid) nanocomposite for smart textile application.

This present study demonstrated the preparation of a highly crystalline anatase (ana) form of titanium oxide (TiO2) doped silk nanocrystal (SNC) nanohybrid (ana-TCS) of diameter (7.5 ± 1.4 nm) by the sol-gel method using titanium (IV) butoxide as the hydrolysis material. This prepared nanohybrid with surface hydroxyl groups acted as a co-initiator for the synthesis of poly(L-lactic acid) (PLLA)-g-ana-TSC nanocomposite with grafted PLLA chains via the in situ polymerization technique, using tin-octoate as a catalyst. The fabricated nanocomposite had a high number average molecular weight of 83 kDa with good processibility. This prepared nanocomposite was hydrophobic in nature, with a contact angle of 105°, which was further enhanced to 122 ± 1° when processed via electrospinning technique into a non-woven fabric. The prepared nanocomposite could degrade up to 43% methylene blue dye in 15 days. This nanocomposite showed no significant molecular weight reduction after 1 h of aqeous treatment, which could be attributed to its hydrophobic nature, inhibiting its degradation. However, 50% degradation was observed for the nanocomoposite whereas, PLLA demonstrated 25% degradation in 15 days, after its end-of-life. Thus, this study revealed that the in situ synthesized PLA-ana-TCS nanocomposite could be targeted for use as a hydrophobic, self-cleaning, dye-degradable fabric.

Crystalline titanium-dioxide nanofinish impregnated on electrospun stereocomplex poly (lactic acid) as non-woven nanotextile with superhydrophilic, anti-shrinkage, dark dyeing and waste dye removal ability for sustainable application.

An environmentally friendly non-woven nanotextile has been prepared using enantiomeric pairs of poly (lactic acid) PLA by electrospinning technique. Solution blending of synthesized high molecular weight (⁓105 Da) poly (L-lactic acid) PLLA and poly (D-lactic acid), PDLA for prolonged time stirring produce solely stereocrystallites (sc). The high crosslinking effect of sc-PLA has played an important role, with multifunctional behaviour on the addition of anatase-TiO2 (a-TiO2) in three different ways (Case-I-III). The high crystallinity of a-TiO2 (~7.14 nm), has been confirmed from XRD and TEM studies as 98 %. The nanofinish as studied in (Case -III) by dipping and drying has decreased the water contact angle for the electrospun sc-PLA nanotextile from highly hydrophobic (132°) to superhydrophilicity after 8 min. An easy demonstration of high temperature treated nanofabric (at 100 °C) has proven to obtain an anti-shrinkage sc-PLA nanofabric. Even, the presence of a-TiO2 has improved the colour strength ability of sc-PLA as a dark dyed nanofabric. The loading of as-synthesized a-TiO2 nanoparticle has enhanced adsorbent dosages for 5TdipscPLA up to 1.44 mg/g of MB dosage, at contact time (8 h), and 68 % methylene blue (MB) removal efficiency under UV irradiation. Thereby, this a-TiO2 impregnated sc-PLA nanofabric tends to dye removal.

Functionalized poly(lactic acid) based nano-fabric for anti-viral applications.

This study endeavoured to explore and fabricate antiviral and antibacterial facemasks using zinc (oligo-lactate) (ZL), developed through a microwave synthesis technique. The prepared nano-fabric layer has excellent antiviral and antibacterial properties against Newcastle Disease Virus (NDV) and E. coli and S. aureus, respectively. Thermogravimetric analysis (TGA) of ZL shows a two-step thermal degradation, which confirms the formation of low molecular weight end group lactyl units with zinc ions. Another investigation using varying ZL concentration and silk nanocrystal (SNC) with poly(lactic acid) (PLA) and electrospinning them into nanofibres led to the fabrication of a facile and sustainable nanofabric that can be utilized as a protective layer for facemasks. Morphological analysis revealed the successful preparation of the nanofabric with proper distribution and uniformity in fibre diameter. Hydrophobicity of the prepared nanofabric confirmed excellent protection from water droplets that may transpire during coughing or sneezing by an infected individual. Breathability and reusability tests confirmed that the prepared facemask could be reused by ethanol washing without compromising its surface properties till 4 cycles. The PLA/ZL nanofabric layer demonstrated 97% antiviral efficacy against NDV in 10 minutes. In conclusion, the electrospun nanofabric layer can be used as a facemask having high hydrophobicity, good breathability, antibacterial, and antiviral properties to control the spread of contagious diseases.

Tailor-made ultra-crystalline, high molecular weight poly(ε-caprolactone) films with improved oxygen gas barrier and optical properties: a facile and scalable approach.

The work presents a facile and scalable approach for fabricating tailor-made ultra-crystalline, high molecular weight biodegradable polymer poly(ε-caprolactone) [PCL] through ring-opening polymerization. Linear homopolymer of PCL were fabricated by tuning the molar ratio of monomer: initiator: catalyst in associated with organometallic catalyst (tin octoate) and a non-toxic and structurally symmetric initiator ethylene glycol (EG). High molecular weight PCL homopolymer formation with molecular weight higher than 90,000 Da was examined by FTIR, NMR and GPC. The ultra-crystalline characteristics (percent crystallinity, %Xc >70%) and unique crystal morphology of PCL were thoroughly scrutinized using DSC, XRD, HRTEM, SAED patterns and POM analysis. The developed protocol for the solvent-free technology allows high conversion ~99% at lowest possible reaction time of 1 h suggesting it a cost effective process, which is scalable to larger volume (5000 mL) without compromising the final product properties. The fabricated ultra-crystalline, high molecular weight PCL films showed good oxygen barrier property (~197 cm3 mm-1 day-1), surface free energy (133.7 mN/m) and optical transparency, recommending its niche in envisioned applications like low temperature flexible packaging and biomedical field.