Search results for "polypropylene"
showing 10 items of 177 documents
Kinetics of ascorbic acid degradation in fruit-based infant foods during storage
2013
The kinetics of ascorbic acid (AA) degradation in a fruit-based beikost product added with AA were determined after storage at 4, 25, 37 and 50 °C during 4, 8, 12, 16 and 32 weeks in plastic polypropylene/ethylenevinyl alcohol vacuum packaging. It was confirmed that AA degradation followed an Arrhenius first-order kinetics, with an activation energy of 20.11 ± 0.33 kcal mol−1. No AA losses at 4 °C were recorded during the entire storage period. In contrast, a time - and temperature - dependent decrease (p the degradation rate decreasing from 50 °C to 25 °C, as expected. AA percentage retention at the end of storage ranged between 6.4% (50 °C/16 weeks) and 100.9% (4 °C/32 weeks).
Modeling elastic properties of short flax fiber-reinforced composites by orientation averaging
2010
Abstract Natural fibers of plant origin, used as reinforcement in polymer matrix composite materials, exhibit highly anisotropic elastic properties due to their complex internal structure. Mechanical properties can be evaluated not only by tests but also by mechanical models reflecting the principal morphological features of fibers. Such a FEM model is applied to estimate the elastic properties of a unit cell of a short-fiber-reinforced composite, an elementary flax fiber embedded in a polymer matrix. Orientation averaging approach is used for prediction of the stiffness of short flax fiber reinforced polymer matrix composite. The numerical estimates of Young’s modulus are compared to the t…
A New Calibration Method for the Accurate Determination of Ethylene Content in Ethylene-Propylene Copolymers by CRYSTEX-IR
2012
Summary: CRYSTEX is a fully automated instrument for the determination of Xylene Solubles in polypropylene and ethylene-propylene copolymers, providing an excellent correlation with gravimetric methods. The instrument can be equipped with a dual band infrared (IR) detector to quantify the ethylene weight percentage (C2%) in the amorphous fraction, and in the whole polymer sample. In this work, a new approach based on multiple linear regression (MLR) models is presented, which makes use of two independent IR absorbance signals acquired simultaneously by the detector. A compromise model to predict directly C2% is proposed, which balances good accuracy and reduced experimental effort. MLR mode…
Calculation of small-angle neutron scattering by macromolecules in the semicrystalline state
1980
The conformation of macromolecules in the semicrystalline state has been studied by various authors with respect to the validity of the adjacent re-entry — or switchboard model by application of small-angle neutron scattering. Analytical as well as Monte-Carlo calculations show that the experimental results for melt crystallized polyethylene and isotactic polypropylene can be interpreted on the basis of the solidification model. In this model it is assumed that crystallization occurs by straightening of coil sequences without a long range diffusion process.
Stiffness and strength of flax fiber/polymer matrix composites
2006
Flax fiber composites with thermoset and thermoplastic polymer matrices have been manufactured and tested for stiffness and strength under uniaxial tension. Flax/polypropylene and flax/maleic anhydride grafted polypropylene composites are produced from compound obtained by coextrusion of granulated polypropylene and flax fibers, while flax fiber mat/vinylester and modified acrylic resin composites are manufactured by resin transfer molding. The applicability of rule-of-mixtures and orientational averaging based models, developed for short fiber composites, to flax reinforced polymers is considered. POLYM. COMPOS. 27:221–229, 2006. © 2006 Society of Plastics Engineers
“Effect of Filler Type and Processing Apparatus on the Properties of the Recycled “Light Fraction” from Municipal Post-Consumer Plastics”
2001
Plastic waste or scraps are generated from two main sources: industrial wastes and post-consumer wastes. By using the flotation method, generally two fractions are obtained from municipal post-consumer wastes: a light fraction, floating on water, and a heavy fraction. The former is essentially made of low and high density polyethylene—LDPE, HDPE—and polypropylene—PP; the heavy fraction is formed by poly(vinyl chloride)—PVC—and poly(ethylene terephthalate)—PET. In this work, the recycling of a light fraction from municipal post-consumer plastics has been studied, considering also the effect of filler type—glass fibres, calcium carbonate and wood fibres—and processing apparatus—discountinous …
Antimicrobial thermoplastic materials for biomedical applications prepared by melt processing
2014
In this work thermoplastic polymers with antimicrobial properties were prepared by incorporating an antibiotic, i.e., ciprofloxacin (CFX), by melt processing. Two different polymers were used as matrices, i.e., polypropylene (PP) and poly(lactid acid) (PLA) and different concentrations of CFX have been incorporated. The antimicrobial properties, the release kinetic and the mechanical performances of the prepared materials were evaluated.
Use of PP-g-OXA in the Compatibilization of PP/LCP Blends
1999
Abstract Adding small amounts of liquid crystalline polymers (LCP) to flexible thermoplastic matrices (FTP) allows to enhance the mechanical and thermomechanical properties. Therefore it is possible to obtain materials with new properties only by simple mixing. A strong shortcoming is the incompatibility between LCP and FTP that leads to materials with very poor properties unusable for commercial pourposes. The presence of a compatibilizer is therefore required. Oxazoline functionality is known to be highly reactive toward many other functional groups and then oxazoline functionalized polymers can be efficiently used as compatibilizer precursors. In this work the compatibilizazion of polypr…
Effect of the processing on the properties of biopolymer based composites filled with wood flour
2008
Wood-polymer composites (WPCs) are well known today in the field of industrial applications, because of several advantages they can grant if compared with mineral filler-polymer composites. These advantages regard the low cost of wood based fillers, the reduced specific weight, the lower hazards for production workers in case of inhalation, the special aesthetic features, environmental issues. The scientific literature reports studies regarding polymer matrices like, for instance, polyethylene and polypropylene, in combination with several natural-organic fillers. However, a limit of these composites is represented by the fact that there is not a full biodegradability: this, in fact, regard…
Effectiveness of organoclays as compatibilizers for multiphase polymer blends - A sustainable route for the mechanical recycling of co-mingled plasti…
2014
We prepare and characterize multiphase systems in which small amounts of recycled polymer, namely polyethylene terephtalate (PET) ground from waste bottles, are dispersed in a co-continuous blend of high-density polyethylene (HDPE) and polypropylene (PP). Some of such ternary systems are also filled with plate-like clay nanoparticles with different polarities, in order to assess their influence on the morphology and mechanical behaviour of the blends. On the basis of preliminary wettability considerations and inspections by means of scanning electron microscopy (SEM), the PET is found to preferentially locate within the PP phase. Such a positioning is desirable in order to minimize the pres…