ABSTRACT
Polyamide microcapsules have gathered significant research interest during the past years due to their good barrier properties; however, the potential of their application is limited due to the fragility of the polymeric membrane. Fully aliphatic polyamide microcapsules (PA MCs) were herein prepared from ethylene diamine and sebacoyl chloride via interfacial polymerization, and the effect of key encapsulation parameters, i.e., monomers ratio, core solvent, stirring rate and time during the polymerization step, were examined concerning attainable process yield and microcapsule properties (shell molecular weight and thermal properties, MC size and morphology). The process yield was found to be mainly influenced by the nature of the organic solvent, which was correlated to the diffusion potential of the diamine from the aqueous phase to the organic core through the polyamide membrane. Thus, spherical microcapsules with a size between 14 and 90 µm and a yield of 33% were prepared by using toluene as core solvent. Milder stirring during the polymerization step led to an improved microcapsule morphology; yet, the substantial improvement of mechanical properties remains a challenge.
ABSTRACT
The direct solid state polymerization (DSSP) of hexamethylene diammonium dodecanoate (PA 612 salt) was investigated for two different salt grades, fossil-based and bio-based. Aliphatic polyamide salts (such as PA 612 salt) are highly susceptible to solid melt transition (SMT) phenomena, which restrain the industrial application of DSSP. To that end, emphasis was given on reactor design, being the critical parameter influencing byproduct diffusion, amine loss and inherent DSSP kinetics. Experiments took place both at the microscale and the laboratory scale, in which two different reactors were tested in terms of bypassing SMT phenomena. The new reactor designed here proved quite successful in maintaining the solid state during the reaction. Scouting experiments were conducted in order to assess the effect of critical parameters and determine appropriate reaction conditions. Fossil-based PA 612 products proved to have a better end-group imbalance in comparison to bio-based ones, which is critical in terms of achieving high molecular weight. Finally, a real DSSP process was demonstrated, starting from PA 612 salt crystals and ending with PA 612 particles.
ABSTRACT
The nature-identical engineered polysaccharide α-(1,3) glucan, produced by the enzymatic polymerization of sucrose, was chemically modified by acylation with succinic anhydride. This modification reaction was initially performed at the micro scale in a TGA reactor to access a range of reaction conditions and to study the mechanism of the reaction. Subsequently, the best performing conditions were reproduced at the larger laboratory scale. The reaction products were characterized via coupled TGA/DSC analysis, FT-IR spectroscopy, solution viscosity and pH determination. The acylation path resulted in partially modifying the polysaccharide by altering its behavior in terms of thermal properties and solubility. The acylation in a solvent-free approach was found promising for the development of novel, potentially melt-processable and fully bio-based and biodegradable ester compounds.
Subject(s)
Glucans/chemical synthesis , Acylation , Hydrogen-Ion Concentration , Polymerization , Succinic Anhydrides/chemistry , Sucrose/chemistry , ViscosityABSTRACT
Food safety authorities have already allowed the use of mathematical models to predict diffusion from plastic food contact materials. These models use the molecular weight of the migrant as a cornerstone parameter that describes the contribution of the migrant to the diffusion process. In this work, the dependence of the diffusion coefficient on the migrant size was examined through fluorescence recovery after photobleaching (FRAP). A model migrant series of fluorescent probes was used, covering a wide molecular weight range. The advantage and originality of the tested migrant series are associated with the fact that the same shape and chemical functionality are maintained regardless of the molecular weight of the migrants. In this way the dependence of the acquired data on parameters other than size is excluded. The same experiments were carried out in dry and hydrated polyamide 6 to evaluate the effect of polymer matrix mobility in the "diffusion-migrant size" relationship. The experimental data were compared to well-known mathematical or semiempirical approaches, verifying that there is a relationship between the diffusion coefficient and the size of the migrant. However, it is demonstrated that this relationship is also affected by the mobility of the polymer matrix, becoming more pronounced as the mobility of the matrix decreases.
