ABSTRACT
Biocomposites suitable for short-life applications such as food packaging were prepared by melt processing and investigated. Biocomposites studied are wheat starch plasticized with two different molecular weight polyols (glycerol and sorbitol) and reinforced with various amounts of microcrystalline cellulose. The effect of the plasticizer type and the filler amount on the processing properties, the crystallization behavior and morphology developed for the materials, and the influence on thermal stability, dynamic mechanical properties and water absorption behavior were investigated. Addition of microcrystalline cellulose led to composites with good filler-matrix adhesion where the stiffness and resistance to humidity absorption were improved. The use of sorbitol as a plasticizer of starch also improved the stiffness and water uptake behavior of the material as well as its thermal stability. Biodegradable starch-based materials with a wide variety of properties can be tailored by varying the polyol plasticizer type and/or by adding microcrystalline cellulose filler.
Subject(s)
Cellulose/chemistry , Plasticizers/chemistry , Polymers/chemistry , Starch/chemistry , Absorption, Physicochemical , Mechanical Phenomena , Temperature , Water/chemistryABSTRACT
Starch isolated from non-edible Aesculus hippocastanum seeds was characterized and used for preparing starch-based materials. The apparent amylose content of the isolated starch was 33.1%. The size of starch granules ranged from 0.7 to 35 µm, and correlated with the shape of granules (spherical, oval and irregular). The chain length distribution profile of amylopectin showed two peaks, at polymerization degree (DP) of 12 and 41-43. Around 53% of branch unit chains had DP in the range of 11-20. A. hippocastanum starch displayed a typical C-type pattern and the maximum decomposition temperature was 317 °C. Thermoplastic starch (TPS) prepared from A. hippocastanum with glycerol and processed by melt blending exhibited adequate mechanical and thermal properties. In contrast, plasticized TPS with glycerol:malic acid (1:1) showed lower thermal stability and a pasty and sticky behavior, indicating that malic acid accelerates degradation of starch during processing.
Subject(s)
Aesculus/chemistry , Biodegradable Plastics/chemistry , Starch/chemistry , Amylopectin/chemistry , Glycerol/chemistry , Malates/chemistry , Microscopy, Electron, Scanning , Rheology/methods , Spectroscopy, Fourier Transform Infrared , Temperature , Tensile Strength , Thermogravimetry , X-Ray DiffractionABSTRACT
Pehuen cellulosic husk was characterized and employed as reinforcement for composite materials. In this research, thermoplastic pehuen starch (TPS) and TPS/poly(lactic acid) (PLA)/polyvinyl alcohol (PVA) composites, reinforced with 5 and 10% of pehuen husk, were prepared by melt-blending. Comparative samples of pehuen TPS and TPS/PLA/PVA blend were also studied. Physical, thermal, structural and mechanical properties of composites were evaluated. Pehuen husk mainly consists of cellulose (50 wt%), hemicellulose (30 wt%) and lignin (14 wt%). In respect to lipids, this husk has only a 0.6 wt%. Its surface is smooth and damage-free and it is decomposed above 325 °C. The incorporation of pehuen husk improved considerably the thermal stability and mechanical properties of the studied composites, mainly in TPS composites. Their thermal stability enhances since biofiber hinders the "out-diffusion" of volatile molecules from the polymer matrix, while mechanical properties could raise due to the natural affinity between husk and starch in the pehuen seed.
Subject(s)
Biocompatible Materials/chemistry , Cellulose/chemistry , Lactic Acid/chemistry , Polymers/chemistry , Polyvinyl Alcohol/chemistry , Starch/chemistry , Materials Testing , Microscopy, Electron, Scanning , Polyesters , Temperature , Tensile Strength , X-Ray DiffractionABSTRACT
BACKGROUND: It has been reported that patients with gestational diabetes have a considerable long term risk of developing diabetes mellitus. METHOD: Glucose tolerance was studied in the 12 months following birth in 155 patients diagnosed by the authors as having gestational diabetes and followed during pregnancy. RESULTS: It was observed that in 48% of the patients alterations persisted (33% glucose intolerance and 15% diabetes mellitus). Glucose tolerance during gestation and the perinatal results were retrospectively analyzed with a relation with the postpartum reclassification being observed. CONCLUSIONS: It was estimated that the percentage of alterations in glucose tolerance persisting postpartum is extremely high, suggesting the need for this test with a double objective: the reclassification of gestational diabetes and the early detection of glucose intolerance and diabetes mellitus.
