The Effects of Reprocessing and Fiber Treatments on the Properties of Polypropylene-Sugarcane Bagasse Biocomposites.

This study explores the reprocessing behavior of polypropylene-sugarcane bagasse biocomposites using neat and chemically treated bagasse fibers (20 wt.%). Biocomposites were reprocessed 5 times using the extrusion process followed by injection molding. The mechanical properties indicate that microfibers bagasse fibers addition and chemical treatments generate improvements in the mechanical properties, reaching the highest performance in the third cycle where the flexural modulus and flexural strength increase 57 and 12% in comparison with neat PP. differential scanning calorimetry (DSC) and TGA characterization show that bagasse fibers addition increases the crystallization temperature and thermal stability of the biocomposites 7 and 39 °C respectively, without disturbing the melting process of the PP phase for all extrusion cycles. The rheological test shows that viscosity values of PP and biocomposites decrease progressively with extrusion cycles; however, Cole-Cole plots, dynamic mechanical analysis (DMA), width at half maximum of tan delta peaks and SEM micrographs show that chemical treatments and reprocessing could improve fiber dispersion and fiber-matrix interaction. Based on these results, it can be concluded that recycling potential of polypropylene-sugarcane bagasse biocomposites is huge due to their mechanical, thermal and rheological performance resulting in advantages in terms of sustainability and life cycle impact of these materials.

Real time detection of lysozyme by pulsed streaming potentials using polyclonal antibodies immobilized on a renewable nonfouling surface inside plastic microfluidic channels.

A composite surface was prepared on cyclic olefin copolymer (COC) microchannels by UV-photografting of polyethylene glycol acrylate (PEGA) and poly(acrylic acid) (PAA) films. A PEGA layer of globular particles with average thickness of 60 nm was formed after 15 min of polymerization. Real time monitoring by pulsed streaming potentials demonstrated the ability of the PEGA layer to inhibit the adhesion of five different nonspecific adsorbing proteins when compared with pristine COC. Roughness determined by atomic force microscopy (AFM) after PAA grafting on COC-PEGA at different UV illumination times suggests that PAA formation is initiated at the free space in between the PEGA particles. Carboxylic groups activated with N-hydroxysuccinimide and N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide were used to bind anti-lysozyme polyclonal antibodies. The composite COC-PEGA-PAA-anti-lysozyme surface demonstrated its ability to detect lysozyme with a dynamic range between 140 and 860 nM. Linearity was maintained even when samples were spiked with 250 nM of cytochrome as interfering species. The equilibrium constant K(eq) for the adsorption of Ly on COC-PEGA-PAA-anti-Ly was estimated to be 2.7 × 10(6) M(-1), and it shows that this kinetic approach of monitoring the surface charge is also useful to estimate affinity interactions for proteins in label free fashion. The regeneration of the surface exhibited an average percentage of recovery of ∼97% for each of six adsorption-regeneration cycles. This feature enables curve calibration on a single microfluidic chip because each point of the curve has a reproducible and renewable surface.

Quantifying surface-accessible quaternary charge for surface modified coatings via streaming potential measurements.

Prior research established that P[AB]-copolyoxetane polyurethanes with soft blocks having A = trifluoroethoxy (CF(3)CH(2)-O-CH(2)-, 3FOx) and B = dodecylammonium-butoxy (C12) are highly effective as polymer surface modifiers (PSMs). These PSMs displayed high contact antimicrobial efficiency against spray challenge that was attributed to surface concentration of quaternary charge. Herein, using a novel cell design and polymer coating process, streaming potential (SP) measurements are reported for estimating accessible surface charge density. Fused-silica capillaries were embedded in flat polypropylene sheets, and the inner capillary walls were coated with neat HMDI-BD(30)-P[(3FOx)(C12)-87:13-5100] (PU-1) and 1 wt % PU-1 in HMDI-BD(50)-PTMO-1000 (base polyurethane 2). Effects of annealing (60 degrees C) and electrolyte flow cycles on near-surface quaternary charge concentration were determined. Neat PU-1 had a constant SP that was cycle-independent and actually increased on annealing. As-cast 1 wt % PU-1 showed initial SPs about half those for neat PU-1, with substantial attenuation over 16 measurement cycles. SPs for annealed 1 wt % PU-1 displayed lower initial values that attenuated rapidly over multiple cycles. Zeta potentials and surface charge densities were calculated from SPs and discussed relative to contact antimicrobial properties. Tapping mode atomic force microscopy (TM-AFM) imaging was employed for investigation of 1 wt % PU-1 surface morphology. Microscale phase separation occurs on annealing 1 wt % PU-1 for 24 h at 60 degrees C. Surprisingly, phase separation was also observed after short immersion of 1 wt % PU-1 coatings in water. The morphological changes are correlated with instability of near-surface charge found by SP measurements. A model is proposed for near-surface spinodal decomposition of metastable as-cast 1 wt % PU-1. The formation of a fluorous modifier rich phase apparently sequesters near-surface quaternary charge and accounts for temporal instability of antimicrobial properties. The results are important in providing a facile method for screening polycation-based, contact antimicrobial coatings for accessible charge density and in assessing durability.

Adsorption kinetics of proteins in plastic microfluidic channels: real-time monitoring of lysozyme adsorption by pulsed streaming potentials.

A proof-of-concept study is presented illustrating the real-time monitoring of lysozyme (Ly) adsorption on the surface of microchannels made with cyclic olefin copolymer (COC). The signal arises from changes in the surface charge upon adsorption of Ly which is monitored by pulsed streaming potentials. Because streaming potentials are electrochemical potentials resulting from the pressure-driven flow of the liquid and the surface charge of the microchannel, this approach is ideal for microfluidics. Initial adsorption rates showed a linear correlation with the bulk concentration of [Ly] in the range between 7.0 and 350 nM. Fitting of the adsorption isotherms allowed the estimation of equilibrium and rate constants of adsorption. The influence of phosphate ions on the adsorption kinetics of Ly was also investigated. Unlike the steady flow used in conventional streaming potential measurements, the present approach incorporates pulsed flow and the ability to inject finite samples into the microfluidic stream. The pulsed flow allows the use of non-reference electrodes which removes the need for special electrolytes to stabilize the electrode potentials. Likewise, the injection permits monitoring of adsorption and desorption events in real time. The label-free monitoring of these events and the high sensitivity of the adsorption kinetics of Ly to solution species found in this work indicates that this method could be applicable to study protein-protein interactions.