pH-sensitive gels: By using a cyclohexane-based scaffold to which various amino acid based substituents can be connected, low-molecular-weight compounds were obtained that can gelate water at very low concentrations. Their modular design (see picture: AA = amino acid(s), X = hydrophilic substituent, dark purple = hydrophobic region, light purple = hydrophilic region), allows tuning of the thermally and pH-induced reversible gel-to-sol transition of their gels.
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For the recycling of carpet and artificial turf the latex backing is often a real stumble block. Many strategies have been developed like freezing the carpet, followed by grinding and subsequent separation of the milled particles. Once it has been separated from its backing materials, PA 6 is relatively easy to depolymerise. This produces fresh caprolactam that can be used to manufacture PA 6 with no loss in quality, and is suitable for further recycling [1]. The comparable process for PA 6,6 is not as easy, but DuPont and Polyamid 2000 have developed and patented a process that depolymerises any mixture of PA 6 and 6,6 using ammonia. The result is fresh caprolactam and 1,6 diaminohexane for manufacture of PA 6 and 6,6 respectively [2]. Obviously a lot of research has been devoted to avoiding latex as a backing like e.g. polyurethane carpet backing systems based on natural oil polyols and polymer polyols [4]. Still carboxylated styrene butadiene is the leading synthetic latex polymer used in EU-27 for carpet backing, followed by styrene-acrylics and pure acrylics. This contrasts with Eastern Europe, Russia, and Turkey where styrene-acrylics dominate, followed by PVAc and redispersible powders [3]. In addition there has been a lot of research into developing alternative backing systems where the backing can easily be removed. Examples are the use of gecko technology [5] or using click chemistry (reversible Diels Alder reactions) [6]. But the best option for recycling is of course to develop carpets based completely on monomaterials. Paper for the 14th Autex World Textile Conference May 26th-28th 2014, Bursa, Turkey.
MULTIFILE
The concurrent self-assembly of new 1,3,5-trisamide-cyclohexane-based low molecular weight hydrogelators and various surfactants in water leads to the formation of self-assembled fibrillar networks with encapsulated micelles. This prototype system presents an example of orthogonal self-assembly, that is, the independent formation of two different supramolecular structures, each with their own characteristics that coexist within a single system.
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Seven new 1,3,5-cyclohexyltricarboxamide-phenylalanine derivatives were synthesized in order to investigate the effect of the amino acid chirality on the gelating properties of these small molecules in water. Gelation tests have shown that enantiomerically pure homochiral 1,3,5-cyclohexyltricarboxamide-L-phenylalanine is a non-hydrogelator as it crystallizes from water, whereas the heterochiral derivatives with either two L-phenylalanine moieties and one D-phenylalanine (LLD), or vice versa (DDL), are very good hydrogelators. Concentration-dependent gel-to-sol transition-temperature (T(gs)) curves for LLD or DDL gels show a sigmoidal behaviour, which is in contrast to the logarithmic curves generally observed for gels derived from low molecular weight gelators (LMWGs). Such sigmoidal behaviour can be related to interactions between fibre bundles, which give rise to intertwined bundles of fibres. Transmission electron microscopy (TEM) images of LLD and DDL gels show a network of thin, unbranched, fibre bundles with diameters of 20 nm. Right-handed twisted fibre bundles are present in the LLD gel, whereas left-handed structures can be found in the DDL gel. Each bundle of fibres consists of a finite number of primary fibres. Gels consisting of mixtures of gelators, LLD and DDL, and nongelators (LLL or DDD) were investigated by means of T(gs) measurements, CD spectroscopy and TEM. Results show that the incorporation of nongelator molecules into gel fibres occurs; this leads to higher T(gs) values and to changes in the helicity of the fibre bundles. Furthermore, it was found that peripheral functionalization of the homochiral derivatives LLL or DDD by means of a second amino acid or a hydrophilic moiety can overcome the effect of chirality; this process in turn leads to good hydrogelators.
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For almost fifteen years, the availability and regulatory acceptance of new approach methodologies (NAMs) to assess the absorption, distribution, metabolism and excretion (ADME/biokinetics) in chemical risk evaluations are a bottleneck. To enhance the field, a team of 24 experts from science, industry, and regulatory bodies, including new generation toxicologists, met at the Lorentz Centre in Leiden, The Netherlands. A range of possibilities for the use of NAMs for biokinetics in risk evaluations were formulated (for example to define species differences and human variation or to perform quantitative in vitro-in vivo extrapolations). To increase the regulatory use and acceptance of NAMs for biokinetics for these ADME considerations within risk evaluations, the development of test guidelines (protocols) and of overarching guidance documents is considered a critical step. To this end, a need for an expert group on biokinetics within the Organisation of Economic Cooperation and Development (OECD) to supervise this process was formulated. The workshop discussions revealed that method development is still required, particularly to adequately capture transporter mediated processes as well as to obtain cell models that reflect the physiology and kinetic characteristics of relevant organs. Developments in the fields of stem cells, organoids and organ-on-a-chip models provide promising tools to meet these research needs in the future.
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