PurposeThe present research investigates tailoring the physical properties of stereolithography (SL) epoxy‐based resins by dispersing controlled small amounts of multi‐walled carbon nanotubes (MWCNTs) directly in SL resins prior to layered manufacturing.Design/methodology/approachA modified 3D Systems 250/50 SL multi‐material machine was used where the machine was equipped with a solid‐state (355 nm) laser, unique ∼ 500 ml vat, overfill drain vat design that continuously flowed resin into the vat via a peristaltic pump, and 8.89 by 8.89 cm2 platform. The vat did not include a recoating system. Pumping the composite resin assisted in maintaining the MWCNTs dispersed over long periods of time (with MWCNT settling times on the order of one week). The research approach required developing a method for dispersing the MWCNTs in SL resin, determining new SL build parameters for the modified resin and SL machine, and building and testing tensile specimens.FindingsMechanical mixing and ultrasonic dispersion provided simple means for dispersing MWCNTs in the SL resin. However, MWCNT agglomerates were observed in all the parts fabricated using the filled resins. Each concentration of MWCNTs resulted in a “new” resin requiring modifications to the SL build parameters, EC and DP. Once characterized, the modified resins performed similar to traditional resins in the SL process. Small dispersions of MWCNTs resulted in improvements in the tensile strength (TS) (or ultimate tensile stress) and fracture stress (FS) of tensile specimens as 0.025 percent (w/v) MWCNTs in DSM Somos® WaterShed™ 11120 resin resulted in increases in TS and FS of 5.7 percent and 26 percent, respectively, when compared to unfilled resin. Increasing the concentration of MWCNTs to 0.10 percent (w/v) resulted in increases in TS and FS of 7.5 percent and 33 percent, respectively, over the unfilled resin. Transmission and scanning electron microscopy showed strong affinity between the epoxy resin and the MWCNTs.Research limitations/implicationsAdditional MWCNT type and concentrations in various SL resins should be investigated along with additional means for dispersion to provide sufficient information on developing new SL resins for unique functional applications.Practical implicationsIt is anticipated that the methods described here will provide a basis for further development of advanced nanocomposite SL resins for end‐use applications.Originality/valueThis research successfully illustrated the dispersion and use of MWCNTs as a reinforcement material in a commercially available SL resin.
Aspergillus niger lipase immobilization by covalent binding on chitosan-coated magnetic nanoparticles (CMNP), obtained by one-step co-precipitation, was studied. Hydroxyl and amino groups of support were activated using glycidol and glutaraldehyde, respectively. Fourier transform infrared spectrometry, high-resolution transmission electron microscopy and thermogravimetric analysis confirmed reaction of these coupling agents with the enzyme and achievement of a successful immobilization. The derivatives showed activities of 309.5 ± 2.0 and 266.2 ± 2.8 U (g support)(-1) for the CMNP treated with glutaraldehyde and with glycidol, respectively. Immobilization enhanced the enzyme stability against changes of pH and temperature, compared to free lipase. Furthermore, the kinetic parameters K m and V max were determined for the free and immobilized enzyme. K m value quantified for enzyme immobilized by means of glutaraldehyde was 1.7 times lowers than for free lipase. High storage stability during 50 days was observed in the immobilized derivatives. Finally, immobilized derivatives retained above 80% of their initial activity after 15 hydrolytic cycles. The immobilized enzyme can be applied in various biotechnological processes involving magnetic separation.
Mango peels is a by-product obtained during mango processing, which is currently discarded causing environmental pollution. In the present study, mango peels were used as source of polyphenols and pectin. Additionally, antioxidant and antifungal activities were measured. The extraction condition to recover pectin and polyphenols at the same time was using water, 121 °C/10 min at 1:40 w/v ratio (9.38 g/100 g dry peels and 72.61 mg/g dry peels, respectively). With this treatment, higher antioxidant capacity was obtained (72.18, 37.73 and 39.23 ppm of total polyphenols from mango peels to inhibit 2,2-diphenyl-1-picrylhydrazyl and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) free radical; also the lipid oxidation inhibition reaction in 50%, respectively). Furthermore, this extract inhibited the radial growth of Colletotrichum gloeosporioides, Sclerotinia sclerotiorum and Mucor sp. in 50% and Fusarium oxysporum in 33.33%. Thus, the results suggest that total polyphenols from mango peels is as attractive alternative source for bioactive compounds, like antioxidants and antifungal molecules.
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