Poly(vinyl chloride), a historical polymer still evolving

Poly(vinyl chloride) (PVC) is one of the commodity polymers of the highest worldwide consumption still in continuous evolution. The recent demonstration of the adaptability of this material for extrusion-based 3D printing techniques opens the possibility of manufacturing a large-scale of tailored flexible and ductile PVC objects, apart from those already registered in the market. The most important characteristics of this polymer from a scientific and technological point of view are described here; i.e., some figures and facts concerning the production and applications and, the two main drawbacks of the polymer: thermal degradation and plasticizer exudation. The most recent efforts and advances to overcome polymer limitations and develop new fields of applications based on modification reactions, in solution, at the surface and in the melt state, as well as the use of PVC formulations in the emerging processing technology of additive manufacturing are addressed.The continuous collaboration of ERCROS with academia on the subject of PVC along last decades and the supply of samples is acknowledged. CM acknowledges the Spanish Ministry of Science, Innovation and Universities, grant number MAT 2020 -83014-C2-2-P

Searching for Rheological Conditions for FFF 3D Printing with PVC Based Flexible Compounds

Rheology is proposed as a tool to explore plasticized poly(vinyl chloride) (PVC) formulations to be used in the fused filament fabrication (FFF) 3D printing process and so manufactures flexible and ductile objects by this technique. The viscoelastic origin of success/failure in FFF of these materials is investigated. The analysis of buckling of the filament is based on the ratio between compression modulus and viscosity, but for a correct approach the viscosity should be obtained under the conditions established in the nozzle. As demonstrated by small amplitude oscillatory shear (SAOS) measurements, PVC formulations have a crystallites network that provokes clogging in the nozzle. This network restricts printing conditions, because only vanishes at high temperatures, at which thermal degradation is triggered. It is observed that the analysis of the relaxation modulus G(t) is more performing than the G″/G′ ratio to get conclusions on the quality of layers welding. Models printed according to the established conditions show an excellent appearance and flexibility, marking a milestone in the route to obtain flexible objects by FFF

Shedding light on the viscoelastic behavior of artificial and human tears: A microrheological approach

12 pags., 9 figs., 3 tabs.This study conducts research on the viscoelastic properties of biological fluids, including both hyaluronic acid-containing lubricating eye drops and human tears, by means of passive microrheology. By tracking the Brownian motion of tracer particles of various sizes in the fluids, we were able to probe their viscoelastic properties. The results showed that the viscoelastic properties of artificial tears, such as Newtonian viscosity and relaxation time, scale to the concentration and macromolecular size of hyaluronic acid, resembling unentangled semidiluted solutions. Moreover, human tears were found to have a viscosity that is 50% greater than that of pure water, comparable to artificial tears containing 0.1% hyaluronic acid, but with a relaxation time one order of magnitude longer than ophthalmic solutions. This behavior was attributed to their intricate composition. The distinctive aspect of this study lies in demonstrating the feasibility of measuring the rheological properties of human tears, a biofluid of great interest, using extremely small sample volumes and microrheology, providing comprehensive information across a wide range of frequencies approaching those corresponding to blinking upon the application of the Cox–Merz rule. These findings are of significant value as they pave the way for future research on small volumes of tears from ophthalmic patientsThis research was supported by the CSIC, Spain—Project No. PIE202250E035, by the Basque Government—Project G.V. SAN 22/11–2022333039, and by the MICINN (Ministerio de Ciencia e Innovacion), Spain—Project No. FISS-21-RD21/0002/0041.Peer reviewe

PET- ran-PLA Partially Degradable Random Copolymers Prepared by Organocatalysis: Effect of Poly(l -lactic acid) Incorporation on Crystallization and Morphology

13 pags., 16 figs., 2 tabs.Polyethylene terephthalate (PET) is a nonbiodegradable polymer whose hydrolytic degradation can take decades. Intensive research has been performed to accelerate its hydrolytic degradation without significantly affecting its properties. In this work, PET was combined with poly(lactic acid) (PLA), a well-known biodegradable polymer, and the effect of PLA content in the crystallization of the PET component has been investigated in detail. To make the process sustainable, PET was polymerized using monomers that can be derived from PET chemical recycling (dimethyl terephthalate) and using organocatalysis (metal-free catalysts). First, low-molecular-weight telechelic PLA was prepared from the organocatalyzed ring-opening polymerization (ROP) of l-lactide followed by step-growth copolymerization with PET oligomers. The random copolymerization was confirmed by Fourier transform infrared (FTIR) and H NMR. We found that PET-ran-PLA copolymers are able to crystallize up to 24 mol % of PLA. Wide-angle and small-angle X-ray scattering (WAXS and SAXS) demonstrated that PLA units interrupt the average crystallizable PET sequences, decreasing its lamellar thickness, melting point, and crystallinity. The temperature dependence of the crystallization rate remarkably switches from nucleation control to diffusion control, as the mol % of PLA approaches the maximum tolerable limit for crystallization. The copolymers exhibited a microspherulitic PET morphology that changed to axialitic at relatively high contents of PLA. Preliminary hydrolytic degradation experiments demonstrate the potential degradation character of the prepared copolymers. If we consider the degradability of the copolymers obtained together with the green synthetic route employed (using dimethyl terephthalate, a monomer that can be obtained from the chemical route for recycling PET), the copolymers produced represent a step toward revalorization of PET recycled monomers for the production of sustainable materials.A.J.M. and H.S. acknowledge European funding by the RISE BIODEST project (H2020-MSCA-RISE-2017-778092). A.J.M. and I.F. acknowledge funding and beam time from ALBA Synchrotron facility through the project: 2017092338 (2018). I.F. acknowledges CONACYT (Mexico) for the Ph.D. grant awarded. A.J.M. acknowledges funding from MINECO, project: MAT2017-83014-C2-1-P

Development of a VR application for binge eating treatment: Identification of contexts and cues related to bingeing behavior in Spanish and Italian patients

The objective of this study was to identify frequent situations and specific cues that produce the craving to binge in Spanish and Italian samples of patients with eating disorders (ED). There were two main aims: to assess transcultural differences in the contexts and cues that elicit food craving; and to develop valid, reliable VR environments for effective cue-exposure therapy (CET) for patients from both countries. Department of Psychiatry, Hospital Germans Tries i Pujol Twenty-six Spanish Keywords: Virtual reality, food craving, binge eating, cue-exposure therapy, clinical sample and 75 Italian ED patients completed an ad hoc questionnaire to assess contexts and cues that trigger the craving to binge. No differences between groups were found. All patients reported experiencing higher levels of craving in the afternoon/early evening and in the late evening/night, between meals, when alone, and more frequently at the end of the week. Being in the dining room, the kitchen, the bedroom, the bakery and the supermarket were the specific situations that produced the highest levels of craving to binge. We used the questionnaire results to develop a virtual reality application for CE

Development of a VR application for binge eating treatment: Identification of contexts and cues related to bingeing behavior in Spanish Italian patients

The objective of this study was to identify frequent situations and specific cues that produce the craving to binge in Spanish and Italian samples of patients with eating disorders (ED). There were two main aims: to assess transcultural differences in the contexts and cues that elicit food craving; and to develop valid, reliable VR environments for effective cue-exposure therapy (CET) for patients from both countries. Twenty-six Spanish and 75 Italian ED patients completed an ad hoc questionnaire to assess contexts and cues that trigger the craving to binge. No differences between groups were found. All patients reported experiencing higher levels of craving in the afternoon/early evening and in the late evening/night, between meals, when alone, and more frequently at the end of the week. Being in the dining room, the kitchen, the bedroom, the bakery and the supermarket were the specific situations that produced the highest levels of craving to binge. We used the questionnaire results to develop a virtual reality application for CET