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In this work, electrospun fibers of poly(butylene adipate-co-terephthalate)/poly(N-isopropylacrylamide), PBAT /PNIPAAm, and ecovio®/PNIPAAm blends were obtained. These blends presented a thermoresponsive behavior including a sudden response to temperature variation between 32 and 35 ºC. The addition of PNIPAAm to PBAT and ecovio® solutions significantly improved the electrospinability of both solutions as blends, allowing them to form rounded fibers without defects and with diameters varying between 1000 and 1700 nm. The analysis of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectra for PBAT/PNIPAAm and ecovio®/PNIPAAm electrospun fibers revealed that the electrospinning process does not lead to the formation of strong intermolecular interactions, such as hydrogen bonds, between the constituents of the studied blends’ electrospun fibers. Significant drop water contact angle variation as a function of temperature was observed for both PBAT/PNIPAAm and ecovio®/PNIPAAm electrospun fibers; both presented PNIPAAm’s hydrophilic-hydrophobic transition in the range between 32 and 35 ºC. Comparing PBAT/PNIPAAm and ecovio®/PNIPAAm electrospun fibers, the former was revealed to be more temperature-sensitive than the latter, regarding changes in wettability as the former presented larger gaps in drop water contact angle values compared to the latter. With these results, these blends in the form of electrospun fibers may have a potential application in the field of cell adhesion/detachment.

In this work, electrospun fibers of poly(butylene adipate-co-terephthalate) (PBAT) and poly(N-isopropylacrylamide) (PNIPAAm) blends, PBAT/PNIPAAm, with different mass ratios, were obtained. For characterization of their morphological, structural, thermal and wettability properties, scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetry (TG), differential scanning calorimetry (DSC) and drop water contact angle (DWCA) measurements were carried out. The optimum conditions determined for electrospinning were: voltage of 25 kV, flow rate of 1.3 mL·h−1 and working distance of 15 cm. The most important result was achieving PBAT/PNIPAAm electrospun fibers with a thermoresponsive behavior and a sudden response to temperature at PNIPAAm’s LCST (lower critical solution temperature). From SEM analysis, the higher the content of PNIPAAm in the blend, the higher the average diameter of the electrospun fibers was; also, the higher content of PNIPAAm in the blend allowed the fibers to be rounded with no presence of beads. From ATR-FTIR analysis, no formation of strong intermolecular interactions, such as hydrogen bonding, between the PBAT and PNIPAAm chains was observed. From TG and DSC analyses, the thermal stability of the PBAT/PNIPAAm fibers remained unchanged in respect to the electrospinning. DWCA measurements for PBAT/PNIPAAm 70/30 and 50/50 fibers, in response to temperature, indicated a gap of 50° to 60° at PNIPAAm’s LCST, evidencing their high thermosensitivity. With these results, PBAT/PNIPAAm electrospun fibers with 30% or more in mass ratio of PNIPAAm might find a potential application for the cell adhesion/detachment field.

Nesse trabalho os parâmetros de miscibilidade foram determinados a partir de medidas viscosimetricas de solucoes diluidas para as blendas de poli(butileno adipato co-tereftalato)/poli(N-isopropilacrilamida) (PBAT/PNIPAAm) e de Ecovio®/PNIPAAm em diferentes proporcoes massicas. Foi verificado que as solucoes das blendas de PBAT/PNIPAAm ate a proporcao massica 70/30 apresentaram tendencia a imiscibilidade, devido aos valores dos parâmetros de solubilidade serem negativos, enquanto as solucoes das blendas de PBAT/PNIPAAm nas proporcoes massicas a partir de 50/50 apresentaram maior tendencia a miscibilidade, pois os valores determinados para os parâmetros foram positivos. Por outro lado, nas condicoes experimentais analisadas, os valores dos parâmetros de miscibilidade obtidos para as blendas de solucoes diluidas de Ecovio®/PNIPAAm foram negativos em todo o intervalo de concentracao avaliado, indicando que essas blendas nao apresentaram tendencia a miscibilidade. Sendo assim, foi possivel inferir que a tendencia a miscibilidade das blendas de PBAT/PNIPAAm ocorreu provavelmente devido as interacoes intermoleculares formadas entre o atomo de nitrogenio do grupo amida do PNIPAAm e o atomo de oxigenio do grupo carbonila da carboxila do PBAT.

RESUMO Neste trabalho foram obtidas fibras eletrofiadas de blendas de Ecovio® e de poli(N-isopropilacrilamida) de alta massa molar (Ecovio®/PNIPAAm AMM) e de baixa massa molar (Ecovio®/PNIPAAm BMM). As fibras de blendas de Ecovio®/PNIPAAm AMM foram obtidas a partir de soluções com concentração de 10% e nas proporções mássicas de 100/0, 85/15, 70/30, 50/50 e 0/100. As fibras de Ecovio®/PNIPAAm BMM foram obtidas a partir de soluções de Ecovio® a 20% com adição 1%, 2%, 3% ou 10% de PNIPAAM BMM. As fibras eletrofiadas foram caracterizadas pelas técnicas de microscopia eletrônica de varredura (MEV), espectroscopia de infravermelho com transformada de Fourier usando acessório de reflectância atenuada (FTIR-ATR) e de medidas de molhabilidade das superfícies das fibras em função da temperatura. Verificou-se que a adição de PNIPAAm AMM às soluções das blendas de Ecovio®/PNIPAAm favoreceu a eletrofiabilidade das soluções, pois as fibras obtidas apresentaram morfologia esférica e ausência de contas, principalmente a partir da proporção mássica de PNIPAAm AMM de 30%. Além disso, a presença de PNIPAAm AMM tornou as fibras de Ecovio®/PNIPAAm termossensíveis. Esse resultado foi observado a partir das medidas de ângulo de contato da gota de água em função da temperatura, que mostraram que a molhabilidade dessas fibras aumentou em temperaturas abaixo de 32 oC e, em temperaturas acima de 32 oC, a molhabilidade diminuiu. Isso ocorreu devido à transição hidrofílica-hidrofóbica, característica do PNIPAAm na faixa de 32-35 °C. Por outro lado, não foi verificado o mesmo comportamento para as fibras de Ecovio®/PNIPAAm BMM, as quais tiveram uma melhora na molhabilidade com a adição de PNIPAAm BMM, mas não apresentaram o comportamento de termosssensiblidade, provavelmente devido ao menor tamanho das cadeias do PNIPAAm BMM, que não favoreceu a transição hidrofílica-hidrofóbica. Assim, provavelmente apenas as fibras eletrofiadas de Ecovio®/PNIPAAm AMM poderiam vir a apresentar potencial aplicação na área de crescimento/descolamento celular. ABSTRACT In this work were obtained electrospun fibers from Ecovio® and poly (N-isopropylacrylamide) high molar mass (Ecovio®/PNIPAAm AMM) and low molar mass (Ecovio®/PNIPAAm BMM) blends. Ecovio®/PNIPAAm AMM blend fibers were obtained from solutions with a concentration of 10% and in the mass ratios of 100/0, 85/15, 70/30, 50/50 and 0/100. Ecovio®/PNIPAAm BMM fibers were obtained from 20% Ecovio® solutions with 1%, 2%, 3% or 10% addition of PNIPAAM BMM. The electrospun fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy using attenuated reflectance enhancement (FTIR-ATR) and fiber surface wettability measurements. The addition of PNIPAAm AMM to the solutions of Ecovio®/PNIPAAm blends favored the electrospinning of the solutions, since the fibers obtained showed spherical morphology and absence of beads, mainly from the 30% mass ratio of PNIPAAm AMM. In addition, the presence of PNIPAAm AMM made Ecovio®/PNIPAAm fibers thermosensitive. This result was observed from water drop contact angle measurements as a function of temperature, which showed that the wettability of these fibers increased at temperatures below 32 ºC and at temperatures above 32 ºC decreased. This was due to the hydrophilic-hydrophobic transition characteristic of PNIPAAm in the 32-35 °C range. On the other hand, the same behavior was not observed for the Ecovio®/PNIPAAm BMM fibers, which had an improvement in wettability with the addition of PNIPAAm BMM, but did not exhibit the thermosensitivity behavior, probably due to the smaller size of the PNIPAAm BMM chains, which did not favor the hydrophilic-hydrophobic transition. Thus, it is likely that only the electrospun Ecovio®/PNIPAAm AMM fibers could have potential application in the area of cell growth/detachment.

The synthesis of new polymeric materials from the monomers is an arduous task, which does not always achieve the desired success. A very promising alternative that grows each year is the chemical modification of existing polymers. In this case, the polymer is one of the reagents of well-known properties and, through conventional chemical reactions, new functional groups can be inserted into the polymer chain, leading to a wide diversity of properties and applications for the new materials obtained. However, for the chemical modification reaction to succeed, it is critical that the polymer has reactive functional groups that can be used in chemical reactions. Polysaccharides are renewable, biodegradable and abundant natural polymers throughout the planet Earth, which have, on average, three hydroxyls in each repeating unit. With these characteristics, they have been extensively used in reactions of chemical modification, to reach biodegradable products, renewable sources and with important physicochemical properties for the industries. In this chapter, we will present different methodologies used in the synthesis of new materials from polysaccharides, as well as the study of their properties and technical feasibility of application in important sectors of the industry.

Zein is a biodegradable and biocompatible material extracted from renewable resources; it comprises almost 80% of the whole protein content in corn. This review highlights and describes some zein and zein-based materials, focusing on biomedical applications. It was demonstrated in this review that the biodegradation and biocompatibility of zein are key parameters for its uses in the food-packing, biomedical and pharmaceutical fields. Furthermore, it was pointed out that the presence of hydrophilic-hydrophobic groups in zein chains is a very important aspect for obtaining material with different hydrophobicities by mixing with other moieties (polymeric or not), but also for obtaining derivatives with different properties. The physical and chemical characteristics and special structure (at the molecular, nano and micro scales) make zein molecules inherently superior to many other polymers from natural sources and synthetic ones. The film-forming property of zein and zein-based materials is important for several applications. The good electrospinnability of zein is important for producing zein and zein-based nanofibers for applications in tissue engineering and drug delivery. The use of zein’s hydrolysate peptides for reducing blood pressure is another important issue related to the application of derivatives of zein in the biomedical field. It is pointed out that the biodegradability and biocompatibility of zein and other inherent properties associated with zein’s structure allow a myriad of applications of such materials with great potential in the near future.

Although the electrospinning (ES) is known for almost 80 years, only in the last two decades this technique has been widely used for obtaining micro- and/or nanofibers. Several aspects contributed for spreading the electrospinning, for instance, the easy operational aspects, affordable equipment, and highly versatile design setup, among others. So, in view of materials chemistry, the electrospinning is one of paramount techniques for processability of polymers and product development at submicrometric scales. This chapter presents the basic concepts of electrospinning of polymeric solutions as well as experimental arrangements commonly employed for different materials. Recent results toward the development of polymer mats published in the literature are discussed as well as the structure/properties relationship. Different applications of electrospun mats are discussed in this chapter. A very large window of opportunities remains opened for developing mats as absorbents for industrial effluent treatments. Solid-phase microextraction analysis is another field in which electrospun mats find the enormous potential of application. The high surface area to volume ratio allows electrospun mats to work as an efficient drug-releasing device even as scaffolds for cell growth and tissue engineering. This chapter is divided in the following sections: The Introduction (in Sect. 1) deals with the basic aspects of electrospinning such as the experimental devices used and the parameters that may influence the morphology and properties of mats; chemical and physical characterization of electrospun mats are discussed in Sect. 2; Sect. 3 shows the most relevant technological applications of electrospun fibers. More than 260 references are provided.

This study describes the stability and rheological behavior of suspensions of poly(N-isopropylacrylamide) (PNIPAM), poly(N-isopropylacrylamide)-chitosan (PNIPAM-CS), and poly(N-isopropylacrylamide)-chitosan-poly(acrylic acid) (PNIPAM-CS-PAA) crosslinked particles sensitive to pH and temperature. These dual-sensitive materials were simply obtained by one-pot method, via free-radical precipitation copolymerization with potassium persulfate, using N,N′-methylenebisacrylamide as a crosslinking agent. Incorporation of the precursor materials into the chemical networks was confirmed by elementary analysis and infrared spectroscopy. The influence of external stimuli such as pH and temperature, or both, on particle behavior was investigated through rheological measurements, visual stability tests, and analytical centrifugation. The PNIPAM-CS particles showed higher stability in acid and neutral media, whereas PNIPAM-CS-PAA particles were more stable in neutral and alkaline media, both below and above the lower critical solution temperature of PNIPAM (stability data). This is due to different interparticle interactions as well as those between the particles and the medium (also evidenced by rheological data), which were also influenced by the pH and temperature of the medium. Based on the results obtained, we found that the introduction of pH-sensitive polymers to crosslinked PNIPAM particles not only produced dual-sensitive materials but also allowed particle stability to be adjusted, making phase separation faster or slower, depending on the desired application. Thus, it is possible to adapt the material to different media. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Recycled PET from bottles was processed from flakes, which containing different amounts of water uptake. After this process, they are subjected to characterization by differential scanning calorimetry (DSC), thermogravimetry (TG), and Fourier-transform infrared spectroscopy with an attenuated total reflectance accessory (FTIR-ATR). From the DSC and TG results it can be postulate an increase in the proportion of short-molecular-weight distribution in the PET chains, due to the hydrolytic degradation of recycled PET during the thermopressing in presence of water. This hydrolytic degradation probably formed more polar groups on the surface of the processed and recycled PET, like carboxyl groups, as observed by FTIR-ATR.

Existe grande preocupação ambiental e econômica quanto à reutilização dos materiais poliméricos pós-consumo, devido ao grande volume de descarte destes nos lixos urbanos e ao valor agregado que esses materiais apresentam. Por isso existem vários estudos relacionados à pesquisa para o desenvolvimento de métodos de reciclagem mecânica e química dessa categoria de materiais, principalmente o PET. Neste trabalho o PET pós-consumo, obtido a partir de garrafas, foi submetido à reciclagem química usando solução de hidróxido de sódio em etilenoglicol. Foi verificado que o rendimento da reação e a cinética de despolimerização foram influenciadas pela velocidade de agitação do meio reacional. A 1360 rpm a resistência ao processo de transferência de massa do produto sólido a partir da superfície das amostras de PET não reagidas para a solução foi eliminada e a reação passou a ser controlada pela etapa química. A equação cinética deduzida a partir do modelo considerando o meio heterogêneo apresentou boa concordância com os resultados experimentais e os valores das constantes de velocidade aparentes foram altos, comparados com valores de outros trabalhos da literatura. Estes resultados sugerem que o meio alcalino usado é bastante eficiente, pois a 1360 rpm e a 170 °C apenas 6 min foram suficientes para obter 100% de tereftalato de dissódio.

The depolymerization of waste poly(ethylene terephthalate) (PETW) flakes from bottles was investigated using a nonaqueous NaOH in ethylene glycol solution and was carried out at patm from 150 to 185 °C, using a NaOH:PET molar ratio of 4:1. The increasing amount of water taken up by the flakes and after submitting them to thermopressing at 260 °C increased the reactivity of the rectangular specimens thermopressed during the depolymerization. At a stirring rate value of 1360 rpm, the product was removed from the unreacted PET surface and the chemical reaction was rate-determining. Using the kinetic model of shrinking core of heterogeneous chemical reaction control, considering the formation and growth of cracks and pores on the polymer surface, the Ea value was 172.7 kJ·mol-1, which was relatively high. However, in the thermodynamic analysis it was shown that the compensation effect of the ΔS⧧ over the ΔH⧧ is sufficiently high to compensate for the high Ea.

The degradation of natural rubber (NR) induced by chloranil and FeCl3, in solution, was investigated by efflux time measurements and by FTIR and 1H NMR spectroscopies. GC–MS was used to investigate the influence of chloranil on residues generated during thermal degradation of NR. 2-Methyl-2-butene (MB) was used as a model compound for the reactions. The results show that the reaction occurs by the scission of the double bond. The reactions were characterised by second-order kinetics, independent of the catalyst. The rate constants determined from efflux time data show a strong contribution of the physical entanglements: if the reactants are diluted 10-fold the value of the rate constant decreases significantly. Thus, the rate constants were more realistically calculated from the changes in the CC concentration measured by 1H NMR. The rate constants for the reaction of MB and chloranil (or FeCl3) are lower than for the corresponding NR degradation. The presence of chloranil does not alter the chromatogram profile obtained by GC–MS for the thermal degradation of NR. It is concluded that chloranil decreases the activation parameters for the degradation because the degradation products are the same as those obtained thermally in absence of chloranil. Activation parameters such as energy, enthalpy, entropy and Gibbs energy were determined. Activation energies (in kJ mol−1) for the degradation of NR are 60.1 for NR/chloranil and 41.9 for NR/FeCl3. From the values of activation parameters, it was suggested that the activation step of the reaction induced by chloranil is more thermally dependent than the reaction induced by FeCl3 that, otherwise, is more entropically dependent.

In this work, poly(N-isopropylacrylamide) (PNIPAAm) was incorporated into previously oxidized PS and PET surfaces by grafting using two photo-initiation pathways. The incorporation of PNIPAAm was observed by drop water contact angle measurements, dyeing with Methylene Blue and AFM images analysis of the virgin and modified polymers. It was verified that the grafting process depends on the chemical surface environment. The grafted surfaces are hydrophilic below 32 °C and hydrophobic above this temperature. The transition is due to the incorporated PNIPAAm. This characteristic gives to the grafted materials potential to be applied as biomaterials.

The present study aimed to study the reaction conditions of grafting of acrylamide on xanthan gum. It was analyzed the influence of reaction conditions, mainly type of initiator activation, initiator concentration and initiator/acrylamide ratio, on graft parameters and copolymer properties. Potassium persulfate was employed as an initiator and heating or N , N , N ′, N ′-tetramethylethylenediamine was used to activate the initiator. Reaction time and initiator concentration were varied and final values for grafting percentage and grafting efficiency were the same for both methods, whereas speed in reaching these values differs from one technique to another. We found that reaction time was inversely proportional to intrinsic viscosity, likely due to main chain degradation promoted by potassium persulfate (KPS); furthermore, the increasing in the KPS concentration lowers grafting percentage, acrylamide conversion and chain degradation, possibly as a result of O 2 formation at high KPS concentrations.