Rheology and Tack Properties of Biodegradable Isodimorphic Poly(butylene succinate)-Ran-Poly(ε-caprolactone) Random Copolyesters and Their Potential Use as Adhesives.

The sole effect of the microstructure of biodegradable isodimorphic poly(butylene succinate)-ran-poly(ε-caprolactone) random copolyesters on their rheological properties is investigated. To avoid the effect of molecular weight and temperature, two rheological procedures are considered: the activation energy of flow, Ea, and the phase angle versus complex modulus plots. An unexpected variation of both parameters with copolyester composition is observed, with respective maximum and minimum values for the 50/50 composition. This might be due to the peculiar chain configurations of the copolymers that vary as a function of comonomer distribution within the chains. The same chain configuration variations are responsible for the isodimorphic character of the copolymers in the crystalline state. Tack tests, performed to study the viability of the copolyesters as environmentally friendly hot melt adhesives (HMA), reveal a correlation with rheological results. Tackiness parameters, particularly the energy of adhesion obtained from stress-strain curves during debonding experiments, are enhanced as melt elasticity increases. Based on the carried-out analysis, the link microstructure-rheology-tackiness is established, allowing selecting the best performing HMA sample considering the polymer chemistry of the system.

Rheology of Polymer Processing in Spain (1995-2020).

The contribution of Spanish scientists to the rheology involved in polymer processing during the last 25 years is investigated. It is shown that the performed research covers, at different levels, all industrial polymeric materials: thermoplastics, thermosets, adhesives, biopolymers, composites and nanocomposites, and polymer modified bitumen. Therefore, the rheological behaviour of these materials in processing methods such as extrusion, injection moulding, additive manufacturing, and others is discussed, based on the literature results. A detailed view of the most outstanding achievements, based on the rheological criteria of the authors, is offered.

Matching Rheology, Conductivity and Joule Effect in PU/CNT Nanocomposites.

We investigated polyurethane (PU)-carbon nanotube (CNT) nanocomposites (PU/CNT) in a range of concentrations from 1 to 8 wt% CNT as hot melt adhesives. We studied the thermal properties of the nanocomposites, which is relevant from an applied point of view. The phase angle plots versus complex modulus results revealed the existence of a maximum above a given CNT concentration. The intensity of the peak and associated relaxation time was analyzed with percolation theory, leading to a new method to determine the rheological percolation threshold. A lower threshold value was obtained from the electrical conductivity data, which was justified recalling that the hopping/tunnelling effect takes place in the nanocomposite, as stated by previous studies in the literature. Joule effect studies indicated that the heating effect was very significant, reaching temperature increases, ΔT, of 60 °C for low voltages. For the first time, the percolation equation was applied to the ΔT to obtain the corresponding threshold. Stimulus-responsive systems were conceived considering the correlation between the ΔT and the conductivity. The case of PU/CNT nanocomposites acting as hot melt adhesives that are welded/unglued by applying/removing an electrical voltage is presented.

How Is Rheology Involved in 3D Printing of Phase-Separated PVC-Acrylate Copolymers Obtained by Free Radical Polymerization.

New auto-plasticised copolymers of poly(vinyl chloride)-r-(acrylate) and polyvinylchloride, obtained by radical polymerization, are investigated to analyse their capacity to be processed by 3D printing. The specific microstructure of the copolymers gives rise to a phase-separated morphology constituted by poly(vinyl chloride) (PVC) domains dispersed in a continuous phase of acrylate-vinyl chloride copolymer. The analysis of the rheological results allows the suitability of these copolymers to be assessed for use in a screw-driven 3D printer, but not by the fused filament fabrication method. This is due to the high melt elasticity of the copolymers, caused by interfacial tension between phases. A relationship between the relaxation modulus of the copolymers and the interlayer adhesion is established. Under adequate 3D-printing conditions, flexible and ductile samples with good dimensional stability and cohesion are obtained, as is proven by scanning electron microscopy (SEM) and tensile stress-strain tests.

Elaboration and Characterization of Conductive Polymer Nanocomposites with Potential Use as Electrically Driven Membranes.

In this work, a general, facile, and relatively low-cost method to produce electrically driven non-porous membranes by revalorization of recycled polyolefins is proposed. The polymer matrices are poly(propylene) (PP) and poly(ethylene) (PE) and their corresponding recycled samples, which are respectively mixed with carbon nanotubes (CNT). The performances of the elaborated nanocomposites are studied by morphological, rheological, and electrical conductivity tests. The Joule heating effect is evaluated by applying an electric field and recording the corresponding temperature rise. An increase of 90 °C is obtained in certain cases, which represents the highest temperature enhancement reached so far by the Joule effect in thermoplastics, to our knowledge. The work shows a route to develop stimulus (voltage)-response (temperature) materials with low cost and with potential applications in many fields. As an example, the increase of the permeability with temperature of membranes made of the indicated nanocomposites, is analyzed.

Ionic supramolecular networks fully based on chemicals coming from renewable sources.

New supramolecular ionic networks are synthesized by proton transfer reaction between a bio-based fatty diamine molecule (Priamine 1074) and a series of naturally occurring carboxylic acids such as malonic acid, citric acid, tartaric acid, and 2,5-furandicarboxylic acid. The resulting solid soft material exhibits a thermoreversible transition becoming a viscoelastic liquid at high temperatures. All the networks show an elastic behavior at low temperatures/high frequencies, with elastic modulus values ranging from 4.5 × 10(6) to 4.5 × 10(7) Pa and soft network to liquid transitions T(nl) between -10 and 60 °C. The supramolecular ionic network based on cationic Priamine 1074 and anionic citrate shows promising self-healing properties at room temperature as well as relatively high ionic conductivity values close to 10(-6) S cm(-1).

Liquid-State and Solid-State Properties of Nanotube/Polypropylene Nanocomposites Elaborated via a Simple Procedure.

Non-modified Multiwalled Carbon Nanotubes (MWCNT) and polypropylene (PP) in absence of compatibilizer have been chosen to elaborate MWCNT/PP nanocomposites using a simple melt-mixing dispersing method. Calorimetry results indicate little effect of MWCNTs on crystallinity of PP, revealing not much interaction between nanotubes and PP chains, which is compatible with the employed manufacturing procedure. In any case, a hindering of polymer chains motion by MWCNTs is observed in the molten state, using oscillatory flow experiments, and a rheological percolation threshold is determined. The percolation limit is not noticed by Pressure-Volume-Temperature (PVT) measurements in the melt, because this technique rather detects local motions. Keeping the nanocomposites in the molten state provokes an electrical conductivity increase of several orders of magnitude, but on ulterior crystallization, the conductivity decreases, probably due to a reduction of the ionic conductivity. For a concentration of 2% MWCNTs, in the limit of percolation, the conductivity decreases considerably more, because percolation network constituted in the molten state is unstable and is destroyed during crystallization.

Facile synthesis of supramolecular ionic polymers that combine unique rheological, ionic conductivity, and self-healing properties.

A new family of supramolecular ionic polymers is synthesized by a simple method using (di-/tri-)carboxylic acids and (di-/tri-)alkyl amines. These polymers are formed by carboxylate and ammonium molecules that are weakly bonded together by a combination of ionic and hydrogen bonds, becoming solid at room temperature. The supramolecular ionic polymers show a sharp rheological transition from a viscoelastic gel to a viscous liquid between 30 and 80 °C. This sharp viscosity decrease is responsible for an unprecedented jump in ionic conductivity of four orders of magnitude in that temperature range. As a potential application, this chemistry can be used to develop polymeric materials with self-healing properties, since it combines properties from supramolecular polymers and ionomers into the same material.

Chemical and rheological properties of the beta-glucan produced by Pediococcus parvulus 2.6.

Some physicochemical and rheological properties of the exopolysaccharide (EPS) produced by Pediococcus parvulus 2.6 were examined. Structural characterization by NMR ((1)H and 2D-COSY) showed that the same EPS, a 2-substituted (1,3)-beta-D-glucan, was synthesized irrespective of sugar source used for growth (glucose, fructose, or maltose). The molecular masses of these beta-glucans were always very high (>10(6) Da) and influenced by the culture medium or sugar source. The steady shear rheological experiments showed that all concentrations of the beta-glucan aqueous solutions exhibited a pseudoplastic behavior at high shear rates. Viscoelastic behavior of beta-glucan solutions was determined by dynamic oscillatory analysis. A critical concentration of 0.35% associated with the appearance of entanglements was calculated. The beta-glucan adopts an ordered hydrogen bond dependent helical conformation in neutral and slightly alkaline aqueous solutions, which was partly denatured under more alkaline conditions.