Sibele Piedade Cestari

Effect of Weathering and Accelerated Photoaging on PET/PC (80/20 wt/wt%) Melt Extruded Blend

In this study we investigated the natural weathering of a catalyzed blend of poly(ethylene terephthalate)/polycarbonate PET/PC (80/20wt/wt%). The results were compared to the accelerated photoaging tests. The specimens were characterized by wide angle X-ray diffraction (WAXD), optical microscopy (OM), thermogravimetry (TG/DTG), medium infrared spectroscopy (FT-IR) and stress-strain analysis. The OM analysis revealed the coexistence of at least three phases – one rich in PET (matrix), the other rich in PC (dispersed droplet) and an interfacial region between them, made of PET/PC copolymer (compatibilizing agent) produced in situ. The TG/DTG curves showed that UV radiation acted mainly on the PET-rich phase and the PET/PC copolymer. The OM and TG/DTG results indicated that the degradation of the compatibilizing agent has had a critical effect on the mechanical properties. For both types of aging (natural and accelerated), the PET’s carbonyl index decreased with the exposure time. The FT-IR results corroborated what was seen in the OM images, showing that the PET phase acts as a shield against the PC degradation. Under accelerated aging, the mechanical properties decreased abruptly - mainly the stress-strain at yield and break - due to the degradation of the in situ compatibilizing agent.

Solid State Polymerization of PET/PC Extruded Blend: Effect of Reaction Temperature on Thermal, Morphological and Viscosity Properties

A systematic study of solid state polymerization (SSP), concerning the melt extruded blend of poly(ethylene terephthalate)/polycarbonate (catalyzed PET/PC, 80/20 wt %), as a function of temperature range (180-190°C) for a fixed time (6 h) is presented. The materials obtained were evaluated by differential scanning calorimetry (DSC), thermogravimetry/derivative thermogravimetry (TG/DTG), optical microscopy (OM) and intrinsic viscosity (IV) analysis. After SSP, at all reaction temperatures, PET glass transition and heating crystallization temperatures slightly decreased, melting temperature slightly increased, while degree of crystallinity was practically invariable. The DTG curves indicated that, at least, three phases remained. The OM images revealed that the morphology is constituted of a PET matrix and a PC dispersed phase. In the interfacial region we noticed the appearance of structures like bridges linking the matrix and the dispersed domains. These bridges were correlated to the PET/PC block copolymer obtained during blending in the molten state. IV increased for all polymerization temperatures, due to the occurrence of PET chain extension reactions - esterification and transesterification. The IV range for bottle grade PET was achieved.

Crystallization Kinetics of Recycled High Density Polyethylene and Coffee Dregs Composites

High density polyethylene (HDPE) – coffee dregs (COFD) composites were studied over a range of seven different temperatures, under isothermal crystallization conditions, using differential scanning calorimetric (DSC) analysis. The aim was to observe the influence of filler content in the crystallization kinetics of HDPE. Seven blends were prepared, the polymer-filler ratio ranging from 100-0 to 40-60%. The results were evaluated using the Johnson-Mehl-Avrami-Kolmogorov equation. The equilibrium melting temperature was determined by applying the Hoffman-Weeks method. The materials were also evaluated through scanning electron microscopy, differential scanning calorimetry and thermogravimetry/derivative thermogravimetry.

Advanced properties of composites of recycled high-density polyethylene and microfibers of sugarcane bagasse

Aiming to systematically convert post-consumer plastics in building materials, we compounded recycled high-density polyethylene and sugarcane bagasse. We ranged the polymer/filler ratio from 100/0 to 60/40, and assessed the properties using optical microscopy, water absorption test, adhesion by tape test, low-field nuclear magnetic resonance, dynamic-mechanical analysis, and wide-angle X-ray diffractometry. The optical microscopy of the triturated bagasse showed the reduced and heterogeneous fiber sizes. The absorption and adhesion test showed that the polymer more heavily filled with bagasse can better absorb and anchor paint with organic solvent base. The dynamic-mechanical analysis and wide-angle X-ray diffractometry led us to believe that the bagasse fibers somehow structured the amorphous region amongst the crystallized lamellae of the polymeric matrix. We concluded that these composites have interesting properties to produce building materials.

Polymer blends of polyamide-6/Spandex fabric scraps and recycled poly(ethylene terephthalate)

In the textile industry, scraps of natural and synthetic polymers in the shape of fibres and yarns are commonly discarded as trash. In order to follow the trends of environmental preservation, we prepared melt-extrusion blends of underwear fabric scraps—made of polyamide-6 and Spandex—and recycled poly(ethylene terephthalate) at five different proportions. The hydrogen low-field nuclear magnetic resonance analysis revealed that there was variation in the molecular mobility of the blends, indicating the interaction of the precursor polymers. The differential scanning calorimetry showed that the crystallization and melting temperatures, and the degree of crystallinity of the recycled polymers, depended on the composition of the blend. The thermogravimetric analysis showed the variation on the initial and maximum degradation temperatures according to the composition of the materials. Through the dynamic mechanical analysis, we observed two intermediate glass transition temperatures, resulting in blends with at least two phases. After selective corrosion, the SEM images revealed voids in the interfacial region of poly(ethylene terephthalate) and polyamide-6 phases. The highest elastic modulus was found for the polyamide-6/Spandex-recycled poly(ethylene terephthalate) (20/80 mass/mass%) blend. In this context, the results suggested the contribution of interchange reactions between ester–amide groups and possibly additional ones (acidolysis, alcoholysis and aminolysis) during the molten processing. The detection of two glass and melting temperatures led to deduce that polyamide-6/Spandex-recycled poly(ethylene terephthalate) formed a partially miscible blend. Thus, this work is line with the sustainability concept, and the material can be reuse for other textile applications.

Sustainable hybrid composites of recycled polypropylene and construction debris

We prepared composites of recycled polypropylene and construction debris aiming to obtain a sustainable hybrid material, with prospective application in the construction industry. We varied the amount of debris in 0, 1, 2, 3 and 7 m/m/% and the compounded materials were analysed by scanning electron microscopy, thermogravimetry/derivative thermogravimetry, differential scanning calorimetry, Fourier-transform infrared spectroscopy, melt flow rate, wide angle X-ray diffractometry, nuclear magnetic resonance relaxation time and dynamic mechanical analysis. The melt flow rate varied non-linearly according to the debris content. The thermal stability of recycled polypropylene was slightly improved due to the presence of debris particles. The degree of crystallinity of the recycled polypropylene also showed a non-linear change, and we noticed some transcrystallization phenomenon in the polymeric matrix. The glass transition temperature decreased for all composites, denoting an increase in the segmental mobility of the polymeric chains. Considering the domains curves of the nuclear magnetic resonance, there was some interaction between polymer and debris particles, mainly ascribed to the nanometric portion of the hybrid debris particles. We concluded that this hybrid composite may become of great interest to the construction industry, used as replacement for closing boards.

Natural and synthetic fillers for reaching high performance and sustainable hybrid polymer composites

According to International Union of Pure Applied Chemistry (IUPAC) a hybrid material is defined as being an intimate mixture of organic components, inorganic components, or both type components. Hybrid polymer composites have embedded a series of natural and synthetic fillers. Each one has intrinsic characteristics that, when combined to a polymer matrix, achieve a high performance and/or sustainable material. The fillers have been recognized to have a large application in the field of polymer composites. Thus, nowadays they have attracted considerable interest among researchers in industry and academia.