Layer-by-Layer Deposition: A Promising Environmentally Benign Flame-Retardant Treatment for Cotton, Polyester, Polyamide and Blended Textiles.

A detailed review of recent developments of layer-by-layer (LbL) deposition as a promising approach to reduce flammability of the most widely used fibers (cotton, polyester, polyamide and their blends) is presented. LbL deposition is an emerging green technology, showing numerous advantages over current commercially available finishing processes due to the use of water as a solvent for a variety of active substances. For flame-retardant (FR) purposes, different ingredients are able to build oppositely charged layers at very low concentrations in water (e.g., small organic molecules and macromolecules from renewable sources, inorganic compounds, metallic or oxide colloids, etc.). Since the layers on a textile substrate are bonded with pH and ion-sensitive electrostatic forces, the greatest technological drawback of LbL deposition for FR finishing is its non-resistance to washing cycles. Several possibilities of laundering durability improvements by different pre-treatments, as well as post-treatments to form covalent bonds between the layers, are presented in this review.

The development of a novel smart material based on colloidal microgels and cotton.

Colloidal microgels are often described as "smart" due to their ability to undergo quite dramatic conformational changes in response to a change in their environmental conditions (e.g. temperature, pH). A range of novel smart materials were developed by the incorporation of colloidal microgels into cotton fabric. A series of microgels have been prepared by a surfactant free emulsion polymerization based on N-isopropylacrylamide (NIPAM) monomer. Poly(NIPAM) is a thermosensitive polymer which undergoes a conformational transition close to the human skin temperature. Poly(NIPAM) was co-polymerized acrylic acid (AA), to prepare pH/temperature-sensitive microgels. Microgel particles were characterized by scanning electron microscopy (SEM), attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy, and dynamic light scattering (DLS). This research aims at coupling microgel particles onto cotton fibers and comparing between different attachment techniques. The coupling reactions between microgels and cotton cellulose are only feasible if they both have appropriate functionalities. For microgels, this was achieved by using different initiators which introduce different functional groups on the particle surface and different surface charges. Cotton samples were successfully modified by carboxymethylation, periodate oxidation, grafting of 1,2,3,4-butanetetracarboxylic acid, and chloroacetylation in order to target possible reactions with the terminal functional groups of the microgel particles. Microgels were attached to the cotton fabrics using different methods and the bonds formed were determined by ATR-FTIR spectroscopy and SEM. The reaction yields were quantified gravimetrically and the maximum weight increase of cotton samples due to the attached microgels was around 24% (w/w).

Synergistic chemo-enzymatic hydrolysis of poly(ethylene terephthalate) from textile waste.

Due to the rising global environment protection awareness, recycling strategies that comply with the circular economy principles are needed. Polyesters are among the most used materials in the textile industry; therefore, achieving a complete poly(ethylene terephthalate) (PET) hydrolysis in an environmentally friendly way is a current challenge. In this work, a chemo-enzymatic treatment was developed to recover the PET building blocks, namely terephthalic acid (TA) and ethylene glycol. To monitor the monomer and oligomer content in solid samples, a Fourier-transformed Raman method was successfully developed. A shift of the free carboxylic groups (1632 cm-1 ) of TA into the deprotonated state (1604 and 1398 cm-1 ) was observed and bands at 1728 and 1398 cm-1 were used to assess purity of TA after the chemo-enzymatic PET hydrolysis. The chemical treatment, performed under neutral conditions (T = 250 °C, P = 40 bar), led to conversion of PET into 85% TA and small oligomers. The latter were hydrolysed in a second step using the Humicola insolens cutinase (HiC) yielding 97% pure TA, therefore comparable with the commercial synthesis-grade TA (98%).

The study of release of chlorhexidine from preparations with modified thermosensitive poly-N-isopropylacrylamide microspheres.

The aim of this study was to investigate and compare the release rates of chlorhexidine (CX) base entrapped in the polymeric beads of modified poly-N-isopropylacrylamides (pNIPAMs) at temperatures below and over the volume phase transition temperature (VPTT) of synthesized polymers: pNIPAM-A with terminal anionic groups resulting from potassium persulfate initiator, pNIPAM-B with cationic amidine terminal groups, and pNIPAM-C comprising anionic terminals, but with increased hydrophobicity maintained by the N-tert-butyl functional groups. The preparations, assessed in vitro below the VPTT, release an initial burst of CX at different time periods between 120 and 240 min, followed by a period of 24 h, when the rate of release remains approximately constant, approaching the zero-order kinetics; the release rates for the polymers beads are as follows: pNIPAM-C>pNIPAM-B>pNIPAM-A. The pattern of release rates at temperature over the VPTT is as follows: pNIPAM-C>pNIPAM-A>pNIPAM-B. In the presence of pNIPAM-C, the duration between the start of the release and the attained minimal inhibitory concentration (MIC) for most of the microbes, in conditions over the VPTT, increased from 60 to 90 min. The release prolongation could be ascribed to some interactions between the practically insoluble CX particle and the hydrophobic functional groups of the polymer.

Evaluation of thermosensitive microspheres as potential components for sun-protectors.

In this study thermosensitive polymeric microspheres obtained in former research were evaluated in vitro for their photoprotective activity. The UVA/UVB ratio was assessed at so called shelf temperature, i.e., at 25 degrees C, and at elevated temperature of 45 degrees C. The evaluated polymers absorb higher levels of UV radiation, when heated from 25 degrees C to 45 degrees C. The MS1 polymer may be defined as polymer with high efficiency in the terms of gaining protection against UVA radiation, when heated. The MS2 absorbs both UVA and UVB radiation, and may be considered, as most protective, when heated to 45 degrees C. The equalized and less strong activity has the polymer MS3 when heated, with lipophilic radical implemented during synthesis.

The influence of increased cross-linker chain length in thermosensitive microspheres on potential sun-protection activity.

The sun protection should involve substances with protecting activity against both UVB and UVA radiation. In this research the evaluation of thermosensitive microspheres as potential molecules for sunscreen formulations was approached, using modified Boots star rating system. The microspheres, thermosensitive N-isopropylacrylamide derivatives, have potential protecting activity against UV radiation. The MX and DX microspheres, with ethylene glycol dimethacrylate and diethylene glycol dimethacrylate crosslinker respectively, due to theirs thermosensitivity exhibit increase in protecting activity against UV radiation when heated to 45 degrees C. The MX microspheres have higher increase in terms of UV absorbance, comparing to DX microspheres, when heated in the 25 degrees C to 45 degrees C range. Studied microspheres have high potential for application as components of sun-screens used in elevated temperatures.

The influence of anionic and non-ionic polymer on adjustment of pH of chlorhexidine preparation including respective solubility aspect.

The solubility of chlorhexidine is highly dependent on the salt present in solution. The aim of present research was evaluation of the effect of two polymers: polyacrylic acid and methylcellulose on the pH of resulting preparation, containing chlorhexidine. Also the solubility aspect was considered in the discussion, as an helpful issue in development in drug form technology. Preparations of chlorhexidine with methylcellulose are characterized by high pH in the range between 9,70-9,98 depending on the temperature of measurements. For preparations of chlorhexidine and polyacrylic acid pH of 5,31-5,72 was evaluated, which was near the physiological values of skin pH. The polyacrylic acid acts as a buffer and enables maintaining of pH near to physiological values. As the connection between polyacrylic acid and chlorhexidine seems to be strong, respective assessments of antimicrobial activity should be performed, to evaluate the applicative value of the preparations.

Effect of ionic and non-ionic polymer on the pH of lidocaine hydrochloride preparation assessed below and over human skin surface temperature.

Lidocaine is widely accepted local anesthetic, which is applied in the form of freely soluble hydrochloride salt. In this study we evaluated the pH of respective solutions of lidocaine hydrochloride with ionic polymer--polyacrylic acid or non-ionic polymer--methylcellulose, and compared to physiological skin conditions in the range between 22 degrees C and 41 degrees C. In microscopic observation of lidocaine hydrochloride preparations with polyacrylic acid the micro-sedimentation was revealed, however obtained mixture was opalescent, and homogenously dispersed in aqueous environment. The pH was maintained on the level not higher then 4,0 in the period of 12 hours for polyacrylic acid formulation, whereas in the case of preparation with methylcellulose, the pH increased from acceptable pH of ca. 4,5 to the level of above 6,0. The polyacrylic acid derivatives should be further studied as vehicles forming preparations with stable pH value during application on the skin, with more specific methods including pH microelectrodes, sufficient for assessments in small quantities of liquids of skin surface.

The influence of lidocaine hydrochloride on environmental pH changes of diluted dispersions of poly(N-isopropylacrylamide) below and over the LCST.

In this study we assessed the influence of lidocaine hydrochloride on the pH of diluted aqueous dispersions of modified poly(N-isopropylacrylamide), at temperature assigned as normalized skin surface temperature, and below and over the lower critical solution temperature value. Three different N-isopropylacrylamide polymer derivatives were synthesized by surfactant free emulsion polymerization, and assessed in the terms of pH in the aqueous dispersions in the presence and absence oflidocaine hydrochloride. The tendency in observed system was similar at three different temperatures, when lidocaine was applied. The pH value increased from the range between 5,39 - 5,90 up to the range 6,22 - 6,55. However, the step of pH between the temperature of 25 degrees C and 32 degrees C was more radical, comparing to 32 degrees C and 45 degrees C. The lidocaine hydrochloride influences the pH patterns observed at various temperature in polymeric systems: measurements of preparations applied on the skin or mucosa should be evaluated in respective temperature range.

The pH changes of diluted dispersions of poly(N-isopropylacrylamide) below and over the LCST in the presence of chlorhexidine.

The pH of diluted aqueous dispersions of modified poly(N-isopropylacrylamide) with chlorhexidine was evaluated, at normalized skin surface temperature, as well below and over the lower critical solution temperature value. Three different poly-N-isopropylacrylamides were synthesized by surfactant free emulsion polymerization. They were evaluated in the terms of pH in the aqueous dispersions in the presence of chlorhexidine. The tendency was similar in all investigated systems at increasing temperature between 25 degrees C and 45 degrees C. The pH value decreased from the range between 9.87-9.94 down to the range 9.38-9.46. The course of pH decrease between the temperature of 32 degrees C and 45 degrees C was more radical, comparing to 25 degrees C and 32 degrees C, however in general the decrease was monotonic. The systems with chlorhexidine tend to change the pH with temperature increase more radically, in the comparison to the chlorhexidine alone. The formulations applied on the skin surface or in the oral cavity should be evaluated in proper temperature spectrum.

The preliminary assessment of chlorhexidine and lidocaine release from preparations of anionic polymer, evaluated by the conductivity measurements.

The aim of this work was the evaluation of conductivity assessments for the monitoring and controlling the release study process of chlorhexidine and lidocaine hydrochloride from the ionic polyacrylic gel, applying different temperatures. According to performed measurements of release, the chlorhexidine, characterized by very low water solubility, is observed in the acceptor compartment in the amount of 2.0-3.0% and its level depends of the temperature. The amount of well soluble lidocaine hydrochloride released in parallel conditions was between 60 and 70%. Beyond, the assessments confirm the presence of a specific bond between the chlorhexidine imine groups and polyacrylic acid carboxylic groups. Presented method may be applied in the prediction of release rates, before actual release analysis, and may assure better evaluation of the systems.

The application of conductivity measurements for preliminary assessments of chlorhexidine and lidocaine hydrochloride release from methylcellulose gel at various temperatures.

For the evaluation of conductivity measurements in the control and monitoring of release process, high number of conductivity measurements was performed. The measurements were done for the compositions of chlorhexidine with methylcellulose, and lidocaine hydrochloride with methylcellulose. Chlorhexidine, a very slightly soluble substance is released from the methylcellulose bead in the amounts ca. 30%-70%, and it depends of temperature of the release process. The lidocaine hydrochloride at the same time is released from methylcellulose formulation in 70-100%. The conductivity in the donor compartment at the start point, and in the acceptor compartment at the termination point, reflect the released amounts of the drug. This study confirms the possibility of application of conductivity measurements for the preliminary assessments of the kinetics of release of soluble and practically insoluble substances from the nonionic polymeric matrix.

The conductivity measurements applied for the evaluation of controlled release of chlorhexidine from thermosensitive N-isopropylacrylamide derivative microgels.

The aim of the work was the evaluation of the conductivity changes in aqueous environment, consisting of chlorhexidine, and N-isopropylacrylamide derivative microgel, during increasing the temperature between 25 degrees C and 42 degrees C, as a prerequisite to develop the this microgel for controlled release of chlorhexidine, when alterations in temperature are involved. Conductivity of studied systems underwent specific alterations, when temperature increased. For the system with polymer PNM I the values of conductivity were in the range 104,47 microS/cm - 134,70 microS/ cm, for temperature range 25 degrees C and 42 degrees C. In the case of PNM II - CX system, respective values reached 91,75 microS/cm - 135,95 microS/cm. The lowest conductivity values were observed when PNM III - CX mixture was studied: 96,90 microS/cm and 117,37 microS/cm. When a complex of derivatives of N-isopropylacrylamide with chlorhexidine undergoes thermal alteration, there is a potential to obtain controlled release of chlorhexidine from the polymeric bead in the range between 25 degrees C and 42 degrees C. The affinity of chlorhexidine to the polymer may be assessed in this systems applying the conductivity measurements. The solubility of chlorhexidine in the polymeric systems should be in future evaluated, to determine role of this factor in the conductivity alterations.

The use of conductometric assessments for development of pulsed release of lidocaine hydrochloride from thermosensitive N-isopropylacrylamide microgels.

The aim of present work was preliminary assessment of the conductivity changes in aqueous compartment, consisting oflidocaine hydrochloride, and N-isopropylacrylamide derivative microgel, during increasing the temperature between 25 degrees and 42 degrees C, as a prerequisite to demonstrate the possibility of applying this microgel for pulsed release of lidocaine hydrochloride, when increased temperature is applied. Conductivity of respective systems composed of polymer and lidocaine hydrochloride were assigned as PNM I-LD, PNM II-LD, and PNM III-LD: obtained values were in the ranges: 39,91 microS/cm - 53,30 microS/cm in the 25 degrees C temperature, 46,14 microS/cm - 56,16 microS/cm in the temperature of 32 degrees C, and 53,30 microS/cm - 118,42 microS/cm at 42 degrees C. During heating or cooling of the microgels derivatives of N-isopropylacrylamide, there is possibility to obtain pulsed release of lidocaine hydrochloride from the polymeric bead in the range between 25 degrees C and 42 degrees C, according to the conductivity measurements.