Polyhydroxybutyrate (PHB) is a sustainable polymer that is a promising candidate for replacing petroleum-based plastics in food packaging. Fillers are used to improve the mechanical properties of PHB composites, simultaneously changing the crystallinity of the polymer matrix. However, it is not well understood how fillers affect crystallisation and microstructure, and thus the resulting mechanical properties of the composite. This review summarises simulation work on polymer nucleation and crystallisation and how nucleation is influenced by different types of polymer-filler interfaces. Experimental studies of PHB composites with a wide variety of fillers are reviewed to find trends between the filler type, crystallinity and mechanical properties. It is clear that fillers act as nucleants that increase the number of spherulites while reducing spherulite size. This behaviour is apparent for almost all fillers regardless of filler chemistry or topology. However, the data obtained from the literature do not seem to produce strong conclusions about the effect of the degree of crystallinity on the tensile properties of PHB-filler composites, although there are some weak trends that indicate the importance of microstructure. In order to enable prediction and control of PHB composite properties, further systematic studies are required to elucidate the effect of specific filler types and the connection between crystallinity, microstructure and mechanical properties. (c) 2022 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Amine absorption (or amine scrubbing) is currently the most established method for CO2 capture; however, it has environmental shortcomings and is energy-intensive. Deep eutectic solvents (DESs) are an interesting alternative to conventional amines. Due to their biodegradability, lower toxicity and lower prices, DESs are considered to be “more benign” absorbents for CO2 capture than ionic liquids. In this work, the CO2 absorption capacity of choline-chloride/levulinic-acid-based (ChCl:LvAc) DESs was measured at different temperatures, pressures and stirring speeds using a vapour–liquid equilibrium rig. DES regeneration was performed using a heat treatment method. The DES compositions studied had ChCl:LvAc molar ratios of 1:2 and 1:3 and water contents of 0, 2.5 and 5 mol%. The experimental results showed that the CO2 absorption capacity of the ChCl:LvAc DESs is strongly affected by the operating pressure and stirring speed, moderately affected by the temperature and minimally affected by the hydrogen bond acceptor (HBA):hydrogen bond donator (HBD) molar ratio as well as water content. Thermodynamic properties for CO2 absorption were calculated from the experimental data. The regeneration of the DESs was performed at different temperatures, with the optimal regeneration temperature estimated to be 80 °C. The DESs exhibited good recyclability and moderate CO2/N2 selectivity.

This work involves the preparation, tensile testing and gas separation characterization of polysulfone mixed matrix hollow fibres filled with polymeric sol based, and subsequently carbonised, xerogels. The pore characteristics of the xerogels were determined using a surface area and porosity analyser. The xerogel materials were reduced to submicron particles by grinding and wet milling, and the resultant particle size was determined using dynamic light scattering. Using dry/wet forced convection spinning, mixed matrix hollow fibre membranes (MMMs) were spun from solutions of polysulfone loaded with the submicron xerogel particles. At 5% loading, all MMMs exhibited higher strain at break and higher strength than unfilled membranes. Compared to unfilled fibres, MMMs were stiffer when filled with hard xerogel inclusions but became more pliable when filled with soft xerogel particles. Knudsen diffusion becomes an important gas transport mechanism in the membranes filled with mesoporous xerogels. When compared to the unfilled hollow fibres, these membranes showed a strong increase in the permeation of low molecular weight, high kinetic diameter gases, leading to a decline in fast/slow gas selectivities. All types of MMM gave higher CO2/O2 (fast/fast) and CH4/N2 (slow/slow) selectivities than unfilled hollow fibres. The MMMs filled with a microporous xerogel gave a higher CO2 pressure normalized flux when compared to the unfilled fibres without sacrificing the CO2/CH4 selectivity. Future work should focus on the tailoring of the pore size of the xerogels and on the wet milling procedure to obtain smaller filler particles.

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Second cheese whey (SCW) is a by-product of cheese and curd cheese production that is usually not recovered and therefore substantially contributes to the negative environmental impact of the cheese manufacture plants. Membrane technology, namely nanofiltration (NF), is used in this work for the recovery of SCW organic nutrients, resulting from "Serpa" cheese and curd production. The SCW is processed by NF to recover a rich lactose fraction in the concentrate and a process water with a high salt content in the permeate. The permeation experiments were carried out in a plate & frame NF unit, where two NF membranes (NFT50 and HR-95-PP) were characterized and tested. The NF permeation experiments were performed accordingly with two different operation modes: total recirculation and concentration. In order to select the best membrane and operating pressure for the SCW fractionation, total recirculation experiments were carried out. The NF modeling was also performed, in terms of permeate fluxes and rejection coefficients using the resistances-in-series model and the solution-diffusion model, respectively. After the membrane selection, the concentration experiments showed that the selected membrane (NFT50) at 3.0MPa allows a water recovery of approximately 80%, concentrating the SCW nutrients approximately 5 times. Therefore, the NF operation can successfully reduce the wastewater organic load and simultaneously contributes to the valorization of the cheese and curd cheese manufacture by-products.

It is experimentally studied herein the effect on pressure drop of scaling down the characteristic length of laminar flows in impermeable rectangular minichannels, its height, to values ranging from 700 to 1200μm with the bottom wall possessing different roughness values. Results are compared to the analytical solution of the Hagen–Poiseuille flow confirming the presence of surface phenomena unobserved in macroscale flows. A fictitious viscosity, μrough, dependent on the surface roughness may be used to model such surface phenomena. This viscosity is obtained from μrough=μapp-μ, μapp being the apparent viscosity used in the theory that matches the experimental data. From the experiments and theory values of μrough ranging from 0.516μ to 0.915μ are obtained. Additionally, effects of suction on pressure drop in the same minichannel, but with permeation through membranes with different roughness values, are also experimentally characterized and analyzed viewing the identification of its attenuating or amplifying trends. Results clearly show that suction reduces the effects of surface phenomena on the pressure drop approaching more closely the Hagen–Poiseuille flow solution. Also, the assumption of fully developed flow is assessed through the numerical calculation of the entrance lengths of the studied minichannel flows and the results elucidated that such hypothesis constitutes a fair approximation: for the most adverse operating conditions, the maximum entrance length is only 17.7% of the channel length.

A model based on steric hindrance mechanisms [1] is used to determine the pore sizes of two ultrafiltration (UF) membranes. The lysozyme rejection coefficients of those membranes are predicted through the same model after modification of the pore size and solute radius by taking into account the development of electric double layers. Two asymmetric cellulose acetate membranes M1 and M2 were prepared and characterized. Membrane M1 has an hydraulic permeability of 2.1 x 10(-6) m/s/bar, a molecular weight cut-off (MWCO) of 30,000 Da and an average pore radius of 2.6 nm. Membrane M2 has an hydraulic permeability of 5.9 x 10(-6) m/s/bar, a molecular weight cut-off (MWCO) of 60,000 Da and an average pore radius of 5.3 nm. Aqueous solutions of lysozyme containing a NaCl concentration of 0.1M were ultrafiltrated through membranes M1 and M2. The predicted lysozyme rejections considering the development of electric double layers on the protein and membrane pore surfaces, are in good agreement with the experimental results.

Diffusion cannot be a major water transport mechanism in osmotic membranes because of the lack of true water concentration gradient within the membrane. Due to the semipermeable property of osmotic membranes, water concentration in the membrane is virtually constant because of the absence of salts. The recently confirmed porous structure of the skin layer of osmotic membranes cannot support the basis to exclude bulk water flow in the membrane as assumed in the classic solution-diffusion model. Herein we demonstrate that the concentration difference of water at the membrane-solution interface manifests itself as a negative hydraulic pressure in the membrane. Hence, the only possible driving force for water movement in osmotic membranes is hydraulic pressure gradient. Osmotically driven membrane processes are characterized with negative pressure within the membrane below the water vapor pressure, inevitably leading to the formation of vapor or small bubbles within the membrane matrix. This phenomenon is expected to markedly reduce the effectiveness of osmotic pressure as a driving force for water transport. Delineation of the breakdown and possible restoration of water continuity under negative pressure is essential for proper understanding of the principles governing water transport in osmotic membranes.

Second cheese whey (SCW) is a by-product of cheese and curd cheese production that is usually not recovered and therefore contributes substantially to the negative environmental impact of the cheese manufacture plants. Membrane technology, namely nanofiltration (NF), is used in this work for the recovery of SCW organic nutrients, resulting from “Serpa” cheese and curd production. The SCW is processed by NF to recover a rich lactose fraction in the concentrate and a process water with a high salt content in the permeate. The permeation experiments were carried out in a plate and frame NF unit, where two NF membranes (NFT50 and HR-95-PP) were characterized and tested. The NF permeation experiments were performed accordingly with two different operation modes: total recirculation and concentration. In order to select the best membrane and operating pressure for the SCW fractionation, total recirculation experiments were carried out. After the membrane selection, the concentration experiments showed that the selected membrane (NFT50) at 30 bar allows a water recovery of approximately 80%, concentrating the second cheese whey nutrients approximately 5 times. Therefore, the NF operation can successfully reduce the wastewater organic load and simultaneously contribute to the valorisation of the cheese and curd cheese manufacture by-products.

Ultrafiltration of a ternary system lysozyme/sodium chloride/water is modelled through the integration of the surface force-pore flow (SFPF) model with the feed flow transport equations and recurring to computational fluid dynamics (CFD). Permeation experiments are performed using an ultrafiltration laboratory cell with a slit feed channel (h=1.2mm≪l=200mm, w=30mm) and a laboratory-made cellulose acetate membrane characterized by an hydraulic permeability of 5.9×10−11ms−1Pa−1 and a molecular weight cut-off of 60kDa. The operating pressures ranged from 2 to 8bar and the salt concentrations from 6×10−4 to 0.1M. The ultrafiltration performance is simulated at different operating pressures and salt concentrations through multicomponent mass transfer modelling with incorporation of membrane/protein electrostatic interactions. The predictions of the lysozyme apparent rejection coefficients and permeation fluxes are in very good agreement with the experimental results.

This paper addresses protein ultrafiltration (UF) and its dependence on UF operating conditions. Cellulose acetate (CA) asymmetric membranes are laboratory made by the phase-inversion method and characterized in terms of pure water permeability, 8.8×10−12 m/s/Pa, and molecular weight cut-off (10000 Da for 98% of rejection). The important feature of the permeation cell is the slit feed channel of 200 mm×30 mm×1.2 mm that simulates the two-dimensional hydrodynamic flow conditions in a spiral wound membrane module. Permeation experiments were carried out for solutions of reference solutes in order to characterize the membranes and for lysozyme solutions under different operating conditions. The influence of the ionic strength in the permeation flux and protein rejection is studied by performing permeation tests with a solution of lysozyme (0.3 kg/m3) containing different NaCl concentrations. Experimentally was observed a decline in the permeate flux with increasing ionic strength. The membrane is almost completely retentive in relation to lysozyme, since the apparent rejection coefficient, ƒ, for this protein is always higher than 95% (in almost all cases, higher than 98%). Two distinct sets of CFD simulations were performed. One to predict the permeation velocities, νp, and another to predict the lysozyme concentration polarization.

A study has been made of the cathodic deposition of cadmium ions from artificial aqueous and dilute solutions produced by the leaching of spent nickel-cadmium batteries. These solutions contained about 20 g/L Cd, 50 g/L Ni and 1 g/L Co. Two types of electrochemical reactors have been used: a parallel-plate reactor and a packed bed reactor with and without solution recirculation. The deposition processes were carried out galvanostatically and the effect of several electrolysis parameters on the recovery of cadmium was analysed. The concentrations of CdSO4 during and after electrodeposition were determined by atomic absorption spectroscopy. The minimum electrode potentials required for electrodeposition to be achieved were established; in addition the composition of the electrodeposits was also estimated. Extraction efficiencies of 80% Cd were achieved. Electrodeposit compositions were about 70% Cd, 10 % Ni, < 0.5% Co, and ∼20% Na2SO4, Fe, oxides. It has been shown that the parallel-plate reactor is the most suitable for our purpose leading to figures of merit with high efficiency values.