Glória Maria Vinhas

Degradation studies on plasticized PVC films submited to gamma radiation

Poly (vinyl chloride), PVC, is a rigid polymer and for several of its applications must be compounded with plasticizing agents. The plasticizers minimize the dipolar interactions, which exist between the polymers chains, promoting their mobility. In this work we studied the properties of PVC/plasticizer systems submitted to different doses of gamma radiation. We have used four commercial plasticizers amongt them di(2-ethylhexyl) phthalate, DEHP, which is present in a great number of commercial applications. The PVC/plasticizer systems have been studied as films made by the solvent evaporation technique. Irradiated and non-irradiated films have been characterized by viscosimetric analysis, mechanical essays and infrared spectroscopy. The results have shown that the rigid, non plasticized, PVC film presented the greatest degradation index, while among the plasticized films the one which presented the larger degradation index due to chain scission was the DEHP plasticized PVC.

A biodegradabilidade da blenda de poli(β-Hidroxibutirato-co-Valerato)/amido anfótero na presença de microrganismos

The increasing consumption of plastics has generated environmental problems because it takes more than a hundred years for a discarded polymer to degrade. The ideal plastic should present desirable industrial properties and be degradable within a satisfactory time period. Researches is conducted to plastics with good properties for packaging, but that are biodegradable when discarded to the environment. In this work we evaluated the biodegradation of the blend of the copolymer poly(hydroxybutyrate-hydroxyvalerate, PHB-HV, which is a natural, biodegradable and biocompatible thermoplastic, and of the starch amphiprotic, in the proportion of 75 and 25% m/m, respectively. The results were obtained through the Sturm test, a methodology for the evaluation of biodegradation in the presence of a mixed culture of Phanerochaete chrysosporium and Talaromyces wortmannii fungi. The results pointed to biodegradation of the blend as a function of the time, with the appearance of terminal carboxylic groups. In addition, a new crystalline symmetry was observed in the polymeric structure.

Evaluation of the types of starch for preparation of LDPE/starch blends

Nesse trabalho foi realizado um estudo sobre diferentes tipos de amido quanto ao crescimento, e a atividade amilolitica de culturas mistas e isoladas dos fungos Phanerochaete chrysosporium e Talaromyces wortmannii. Avaliaram-se tambem as propriedades termicas e mecânicas das blendas de polietileno/amido anfotero (na proporcao 80/20 (m/m)) antes e apos a inoculacao das culturas mistas desses fungos.O amido regular Amidex 3 e o amido modificado Fox5901 foram os que se destacaram quanto ao crescimento celular e producao da enzima amilase. Apesar do pouco tempo de exposicao dos filmes com os fungos, pode-se concluir que os microrganismos promovem mudancas fisicas e quimicas na estrutura da blenda, modificando suas propriedades termicas e mecânicas. A alteracao do grau de cristalinidade e das propriedades mecânicas das blendas podem ser indicios da modificacao provocada pelo processo de biodegradacao.

Estudo de propriedades de PVC modificado com grupos alquila e benzila

Poly(vinyl chloride) (PVC) ranks second among the most consumed thermoplastics in the world, and is considered the most versatile plastic. This versatility arises from its properties and suitability to a variety of transformation processes. The resin is non toxic and inert, therefore the choice of additives having these properties allows for the fabrication of films for food packaging and medical products. On the other hand, the PVC properties can be altered by sterilization processes, in particular through gamma radiation. In this paper we present a study of the flexibility and stability to gamma radiation of chemically-modified PVC. PVC was modified through substitution of chlorine by alkyl and benzyl groups using Grignard reagents. Modified PVC samples were characterized by proton nuclear magnetic resonance (1H NMR) spectroscopy, infrared spectroscopy and differential scanning calorimetric analyses. Degradation of the polymers when submitted to gamma irradiation was evaluated by their viscometric parameters. The modified PVCs generally presented higher stability to gamma radiation than the original polymer. The benzyl substituted polymer exhibited the highest stability when submitted to the sterilization dosage of 25 kGy. The modified PVCs presented glass transition temperatures slightly lower than the original polymer pointing to an increase in flexibility due to the presence of alkyl and benzyl groups as substituents in the main chain.

Effect of the radiolitic sterilization in polyethylene/starch blends

Samples of LDPE/modified starch blends 80/20 m/m before and after exposure to gamma rays were examined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. The effect of gamma radiation is clearly seen in the samples irradiated at a dose of 25 kGy. The main alteration in the polymeric material after exposure at the radiation range was a decrease in the mechanical properties, alterations in the chemical structure of the blend with an increase in the carbonyl and vinyl indices and the appearance of new crystalline symmetry generating a crystalline domain not existing before in the blend.

Evaluation of photodegradation in LDPE/modified starch blends

Photodegradation of LDPE/modified starch blends 80/20 m/m has been examined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X ray diffraction (DRX) before and after exposure to ultraviolet radiation (UV). Samples were exposed to UV in the laboratory for periods of 6, 24, 48 and 60 hours. The main alteration in the polymeric material after exposure to the radiation was a decrease in the mechanical properties, tensile strength and elongation. There were also changes in the chemical structure of the blend with an increase in the carbonyl and vinyl indices, 65.58 and 53.29%, respectively. The analysis of the blend crystallinity pointed to the formation of a new crystalline symmetry that did not exist before the irradiation.

Production of Bacterial Cellulose by Gluconacetobacter hansenii Using Corn Steep Liquor As Nutrient Sources

Cellulose is mainly produced by plants, although many bacteria, especially those belonging to the genus Gluconacetobacter, produce a very peculiar form of cellulose with mechanical and structural properties that can be exploited in numerous applications. However, the production cost of bacterial cellulose (BC) is very high to the use of expensive culture media, poor yields, downstream processing, and operating costs. Thus, the purpose of this work was to evaluate the use of industrial residues as nutrients for the production of BC by Gluconacetobacter hansenii UCP1619. BC pellicles were synthesized using the Hestrin–Schramm (HS) medium and alternative media formulated with different carbon (sugarcane molasses and acetylated glucose) and nitrogen sources [yeast extract, peptone, and corn steep liquor (CSL)]. A jeans laundry was also tested. None of the tested sources (beside CSL) worked as carbon and nutrient substitute. The alternative medium formulated with 1.5% glucose and 2.5% CSL led to the highest yield in terms of dry and hydrated mass. The BC mass produced in the alternative culture medium corresponded to 73% of that achieved with the HS culture medium. The BC pellicles demonstrated a high concentration of microfibrils and nanofibrils forming a homogenous, compact, and three-dimensional structure. The biopolymer produced in the alternative medium had greater thermal stability, as degradation began at 240°C, while degradation of the biopolymer produced in the HS medium began at 195°C. Both biopolymers exhibited high crystallinity. The mechanical tensile test revealed the maximum breaking strength and the elongation of the break of hydrated and dry pellicles. The dry BC film supported up to 48 MPa of the breaking strength and exhibited greater than 96.98% stiffness in comparison with the hydrated film. The dry film supported up to 48 MPa of the breaking strength and exhibited greater than 96.98% stiffness in comparison with the hydrated film. The values obtained for the Young’s modulus in the mechanical tests in the hydrated samples indicated low values for the variable rigidity. The presence of water in the interior and between the nanofibers of the hydrated BC only favored the results for the elasticity, which was 56.37% higher when compared to the dry biomaterial.

Reciclagem química do PET pós-consumo: caracterização estrutural do ácido tereftálico e efeito da hidrólise alcalina em baixa temperatura

Due to the environmental impact caused by PET packaging disposal, this material recycling has been thoroughly discussed and evaluated. In particular, chemical recycling enables achievement of the monomers that are used in PET resin manufacture: ethylene glycol (EG) and terephthalic acid (PTA). Therefore, studies for this process optimization are important from environmental and economic points of view. The present study investigated certain parameters that influence the depolymerization reaction of PET post-consumer via alkaline hydrolysis in order to obtain PTA. Assays were performed at 70 °C by varying the concentration of sodium hydroxide and the reaction time. The best results were obtained at 10.82 mol L-1 NaOH and 9 h reaction time. Consequently, it was possible to prove this process viability, once analyses by infrared and nuclear magnetic resonance confirmed that PTA was obtained in all reactions performed.

Efeito da adição de PHB na cristalização a frio do PET

The present work is concerned with the effect of low concentrations (0.5 e 1.0%) of poly(3-hydroxybutirate) (PHB) on the isothermal cold crystallization of poly(ethylene terephthalate) (PET). Energy curves were obtained by differential scanning calorimetry (DSC) and the kinetics of the crystallization was analyzed using Avramis method. Two crystallization stages were observed. Results showed that the presence of PHB affects the crystallization rate of PET, as verified by changes in the time needed to reach 1, 10, 30, 50 and 99% of crystallinity. Activation energies for the two crystallization stages were computed using Arrhenius plots; PET/PHB mixtures showed slightly smaller values. The equilibrium melting temperatures were estimated according to the procedure of Hoffman and Weeks; the higher values obtained for the PET/PHB mixtures suggest that PHB affects the crystalline structure of PET.

Dyeing of bacterial cellulose films using plant-based natural dyes

The aim of this work was to test the use of plant-based natural dyes on bacterial cellulose (BC) to add aesthetic value to dyed pellicles while maintaining the mechanical properties. Natural pigments from Clitoria ternatea L. and Hibiscus rosa-sinensis were tested. The commercial ARAQCEL RL 500 was also used for comparison purposes. The behavior of biocellulose regarding dye fixation, rehydration, tensile strength, and elasticity was evaluated in comparison to the dried biomaterial, showing that dyeing is a process that can be performed on hydrated BC. Dyeing the BC films through an innovative process maintained the crystallinity, thermal stability and mechanical strength of the BC and confirmed the compatibility of the membrane with the dyes tested, from the observed Scanning Electron Microscopy (SEM) morphology of nanofibers. Dyed biomaterial can be applied to various products, as confirmed by the results of the mechanical tests. As environmental awareness and public concern regarding pollution increase, the combination of natural dyes and BC pellicles can produce an attractive new material for the textile industry.