Eloisa B. Mano

Study of the effect of gamma irradiation on polyolefins—low-density polyethylene

Many of the physical, chemical and utility properties of polymer materials can be altered by means of high energy radiation such as gamma-rays, neutrons and electron beams. In the present work the exposure to gamma radiation of a bulk virgin low density polyethylene (LDPE) was carried out at various doses up to 2000 kGy. The study of the irradiation effects on the material properties has been make by different methods in an integrated way. The experimental data indicate that the gel content, the hardness and the yellowing increase with gamma radiation dose and that the LDPE gamma irradiation process involves crosslinking at lower doses and chain scission at higher doses. The final results show the reliability of gamma radiation as a practical method for the control of long-term properties.

Thermal behavior of gamma-irradiated recycled polyethylene blends

The interest on recycled materials from post-consumer polymers present in discarded commercial packaging has gained increasing attention. The development of new engineering materials based on degraded polymers is an interesting possibility. Blends of low cost plastics such as polyolefins, polystyrene, poly(vinyl chloride), discarded in urban waste are of particular interest. The Instituto de Macromoleculas had developed a two-step process for recovering plastic residues which allows to obtain materials with good properties. One of these materials may be used as plastic lumber and consists of a recycled 75/25 LDPE/HDPE partially degraded blend. The exposure of this blend to low doses of 60Co gamma radiation improves its mechanical properties due to partial crosslinking. Differential scanning calorimetry, gel permeation chromatography, infrared spectroscopy and X-ray diffraction have been used to investigate the effects of gamma irradiation on the thermal behavior of polymer material. The melting and crystallization temperatures were found to decrease as the radiation dose increases, showing a tendency to stabilization at higher values. The correlation of the degradation process, melting heat and molecular weight distribution is discussed.

Characterization of degradation on gamma-irradiated recycled polyethylene blends by scanning electron microscopy

The recycling of polymer blends has gained increasing attention in the world due to economic and environmental considerations. The exposure of recycled polyethylene blends to low doses of 60Co gamma radiation improves their mechanical properties due to crosslinking. It is agreed that gamma irradiation in air may cause degradation with oxidation occurring near the surfaces. Usually degradation means worsened properties. Then, it is important to estimate the extent of oxidation depth under those conditions. Samples of recycled polyethylene blends after exposure to gamma rays were examined by scanning electron microscopy (SEM). Permanganic reagent, developed for revealing semicrystaline morphologies in polyolefins under the electron microscope, has been used to monitor the superficial degradation. A detailed characterization of the material behavior has been made by mechanical and physico-chemical testing. The data presented in this article for recycled polyethylene blend after exposure to gamma rays in the air provide evidence of that the increase of radiation dose promotes a higher surface degradation. The effect of gamma radiation is clearly seen in the specimens irradiated with different doses and may be related to the changes in the mechanical properties.

Gel fraction measurements in gamma-irradiated ultra high molecular weight polyethylene

Abstract Ultra high molecular weight polyethylene (UHMWPE) was irradiated at room temperature in air using an industrial 60Co γ-source. Samples were exposed to integrated doses of 50, 250, 500, 750, 1000, 1500 and 1750 kGy and the soluble part of each irradiated specimen was extracted by exposure to refluxing boiling xylene solvent for 10 h using the Soxhlet method. From such extractions, the swelling ratio and the gel fractions were determined. It was found out that an increase in radiation dose leads to an increase in the gel fraction and a simultaneous decrease in the swelling ratio. These tendencies are attributed to the formation of a crosslinked network.

Tensile behavior of irradiated recycled polyolefin plastics

Solid wastes represent a potential source for raw materials in the world. In Brazil, municipal solid waste (MSW; 2-%) is expected to grow at a rate per year higher than the worldwide rate (1%). On the other hand, the consumption of polymer blends increases at a rate more than twice that of all plastics. Therefore, the recycling of polymeric blends has gained increasing attention in the world due to economic and environmental considerations. A two-step process, developed at the Institute (IMA/ UFRJ), allows one to recover plastic residues and permits the production of materials with controllable composition and homogeneous characteristics. The compression behavior of polyblends, composed of typical polymers that appear in domestic wastes-low and high polyethylenes-can be improved by gamma irradiation. In the present work, the tensile behavior of recycled 75/25 blends of low-density polyethylene (LDPE) and high-density polyethylene (HDPE), after exposure to gamma rays in the air, was investigated. Tensile testing, scanning electron microscopy, infrared and solid-state 13 C-nuclear magnetic resonance spectroscopy, as well as gel content were used to study the effect of gamma irradiation on the polymer blends. The tensile strength was found to increase with radiation dose while the elongation at break decreased. Our experimental results indicate that the gamma irradiation degradation process involves crosslinking at lower doses and chain scission at higher doses.

Comportamento térmico, mecânico e morfológico de compósitos de polietileno de alta densidade reciclado com fibra de piaçava

The use of natural fibers as reinforcement for thermoplastics, especially for recycled thermoplastics, has generated much interest due to their low cost, possibility of environmental protection and use of locally available renewable resources. In this work we evaluate the thermal, mechanical and morphological properties of composites of recycled high-density polyethylene (HDPE-r) with treated and untreated piassaba fibers (Leopoldinia piassaba) in different proportions (5, 10 and 15% w/w). The objective of this work is to obtain composites of HDPE-r / piassaba fiber in order to fulfill the needs of the consumer market, aiming at preparing low-cost plates for light duty jobs. Fibers were submitted to superficial treatment with silane in two different ways: direct incorporation and treatment with methanolic solution of the coupling agent. The results show that composites of HDPE with silane-treated-only fiber had better mechanical performance than methanolic solutions of silane; the increase on fiber - polymer matrix interface adhesion, as revealed from morphological analysis, can explain this higher performance. Thermal stability of the composites is not greatly affected with the addition of treated fiber.

Compatibility of iPP/HOCP binary blends by OM, DSC, DMTA and 13C nuclear magnetic resonance

Abstract The study of miscibility of the isotactic polypropylene (iPP)/hydrogenated oligo(cyclopentadiene) (HOCP) blends was performed by using OM, DSC, DMTA and 13C NMR techniques. The proton spin-lattice relaxation time in the rotating frame by using 13C spectra cross-polarization/magic-angle spinning (CP/MAS) of iPP, HOCP and their blends were determined. These blends showed phase separation. Two amorphous phases were observed: one rich in the high molecular weight component (iPP) and another one rich in the low molecular weight component (HOCP). This behaviour was similar to one observed for HDPE/HOCP blends. The results indicated that compression moulded samples of iPP/HOCP blends formed a partially miscible system, while in literature it was found that extruded isotropic films of this blend displayed as a miscible system. The iPP-HOCP interaction is influenced by the composition, the crystallization process, the solidification time and the specimen preparation.

Caracterização do Sistema Éter Diglicidílico do Bisfenol A/Poliaminas Alifáticas

Diglycidyl ether of the bisphenol A (DGEBA), product DER 331 and hardener 24 system marketed by Chemical Dow of Brazil were characterized by spectroscopic, calorimetric and determination of functional groups methods. The hardener 24 is constituted by triethylenetetramine (60 % molar) and a mixture of ethylene polyfunctional amines with linear, ramified and cyclic structures. The epoxy equivalent of the resin corresponds to 187 g eq -1 . The functionality average, equivalent amine, and the concentration of the hardener that satisfy the stoichiometry corresponds to 5.54, 27.5 g eq -1 , and 14.7 phr, respectively. The epoxy system displayed an enthalpy of reaction of 486 J g -1 (106.6 kJ eq -1 ), and a glass transition temperature (Tg ¥ ) of 124 °C. Also presented in this work is a cure program in two stages where the maximum conversion was reached.

Brittle–ductile transition of gamma-irradiated recycled polyethylenes blend

Abstract During the last few years interest in the development of new engineering materials from post-consumer polyolefins present in discarded commercial packaging has increased. These materials can be used as potential substitutes for products made from non-renewable, synthetic polymers. Our Institute has developed several such materials with good properties using plastic residues found in urban waste. One of these materials is a recycled 75/25 blend of outdoors, partially degraded low density polyethylene (LDPE) and high density polyethylene (HDPE). The exposure of this blend to low doses of 60 Co gamma -radiation improves its compression strength as a result of partial crosslinking. In this work the brittle–ductile transition temperature (BDTT) of this recycled blend was evaluated after exposure to gamma -radiation (100 and 500 kGy) in the presence of air. The experimental results show that the BDTT changes with the irradiation doses. The higher doses cause an increase in the Charpy impact values and a decrease in the BDTT. Gel permeation chromatography, mechanical tests and scanning electron microscopy were used to investigate these effects in the polymer material.

Morphological, Structural, Thermal and Mechanical Characterization of Piassava Fibers

Abstract For the purpose of evaluating the suitability of piassava fiber as reinforcement of polymer matrix (recycled polyethylene), we carried out extensive characterization of morphological, structural, thermal, and mechanical properties of two species of piassava fibers, namely Leopoldinia piassaba (Amazon, Brazil) and Attalea funifera (Bahia, Brazil). Scanning electron microscopy images revealed that each fiber is essentially a composite in which rigid cellulose microfibrils are embedded in a soft lignin and hemicellulose matrix. In addition, the tubular microfibrils are helically wound along the fiber axis forming ultimate hollow cells. An irregularly dimensioned mass, composed mainly of silica, appears on the surface of each fiber. The crystallinity of L. piassaba is found to be inferior to that of A. funifera. On the other hand, thermal analysis shows that both species start to decompose at approximately similar temperature (∼265°C), and that the moisture content in each is approximately 4 to 5%. The mechanical properties correlate well with the fiber diameter. Finally, the L. piassaba, as compared with A. funifera, is softer and more ductile.