Mechanical recycling of polylactide, upgrading trends and combination of valorization techniques

The upcoming introduction of polylactides in the fractions of polymer waste encourages technologists to ascertain its valorization at the best quality conditions. Mechanical recycling of PLA represents one of the most cost-effective methodologies, but the recycled materials are usually directed to downgraded applications, due to the inherent thermomechanical degradation affecting its mechanical, thermal and rheological performance. In this review, the current state of mechanical recycling of PLA is reported, with special emphasis on a multi-scale comparison among different studies. Additionally, the applications of physical and chemical upgrading strategies, as well as the chances to blend and/ or composite recycled PLA are considered. Moreover, the different valorization techniques that can be combined to optimize the value of PLA goods along its life cycle are discussed. Finally, a list of different opportunities to nurture the background of the mechanical recycling of PLA is proposed, in order to contribute to the correct waste management of PLA wastes

Influence of Polyolefin Contamination on the Thermal Characteristics of Bottle Grade Recycled Polyethylene Terephthalate

During the mechanical recycling, especially during the sorting and separation process of bottle grade PET, cross contamination with polyolefin is inevitable. Very small number of polyolefin bottles, caps and closures pass through the separation process and get recycled with PET bottles and affect the final characteristics of the recyclate. The effect of this cross contamination and the influence of polyolefin contamination on the overall characteristics of bottle grade recycled PET, especially the thermal characteristics with emphasis on crystallinity, were thoroughly investigated. The investigation showed that the inclusion of polyolefin contamination influenced the overall characteristics of the bottle grade rPET matrix and indicated incompatibility of polyolefin contaminants and rPET-bg. This influence had an impact on the viscosity, elasticity and strength of the rPET-bg matrix. Furthermore, the crystallinity of the rPET-bg matrix showed the impact of polyolefin contamination as a result of variation of cooling rates and that cross-linking and chain branching predominated over chain scissions as a result of repetitive extrusions. The crystallisation process of the non contaminated rPET-bg and rPET-bg contaminated with polyolefin depended on many influencing factors, such as impurities, cross-linking, chain branching, chain scissions, cooling rates and repetitive extrusion cycles. Also, the crystallisation mechanism fully depended on the nucleation and growth rates and that competition between nucleation and molecular mobility was influenced by the variation of cooling rates and repetitive extrusion cycles. As a result, the thermal characteristics were greatly influenced by the inclusion of polyolefin contamination, especially crystallinity, as shown and validated by the Avrami and Ozawa models and that the findings are a step forward and an original insight on the influence of polyolefin contamination at industrial scale

Effect of multiple extrusions and influence of PP contamination on the thermal characteristics of bottle grade recycled PET

The thermal characteristics of bottle grade recycled PET pellets contaminated with 5% PP prepared by multiple extrusions were studied by differential scanning calorimetry (DSC) at constant heating rate of 10 degrees C/min for various extrusion cycles. The peak temperature of crystallization Tc, the enthalpy of crystallization dHc and the degree of crystallinity Xc were found to be dependent on the number of extrusion cycles. From the dependence on extrusion cycles, the analysis of the crystallization mechanism by Avrami model has been determined, the Avrami exponent n and the rate constant Zt were calculated and the influence of the 5% PP on the bottle grade recycled PET matrix during multiple extrusions and its effect on crystallinity was thoroughly discussed

PHYSICAL ACTIVITY AND HEALTH OF YOUTH

Abstract Development of voluntary control of movement begins in infancy and progresses into childhood as the child attains postural, locomotor and prehensile control. With the refinement of walking, control of locomotor and manipulative abilities improves so that a considerable amount of independent action is possible. These basic movement patterns are the foundation upon which other movements and combinations of movements are subsequently developed and refined. And, movement is the substrate of physical activity. The development of motor competence during early childhood is the outcome of the interaction of the growing, maturing and developing child with his/her environments. Child-environment interactions should be viewed in the context of changing body dimensions and proportions (body scaling) and improving levels of motor competence (action scaling). Body size, proportions and composition change as the child grows, and levels of motor proficiency change as the child develops. These in turn influence the interactions between the child and his/her environments, specifically home, day care and nursery school. An additional factor is the emergence of the child's perception of these environments as they relate to his/her physical and motor characteristics. There is increasing interest in relationships between proficiency in basic movement skills and habitual physical activity in young children. Evidence indicates that specific motor skill instructional and physical activity interventions are associated with improvements in basic movement skills in preschool children. By inference, improving the motor proficiency of young children has the potential to enhance levels of habitual physical activity beyond the preschool years. Moreover, motor coordination is an important predictor of physical activity during middle childhood. Given current concern for the worldwide obesity epidemic, the movement proficiency of overweight and obese children is receiving more attention. Although the issue of reduced physical activity in obese children is somewhat equivocal, one can inquire whether proficiency in movement skills influences activity in obese children and adolescents. The teaching of skills, rules and strategies of a sport is often indicated as an objective of youth sport programs. Observations would suggest that this objective is generally achieved. Specific evidence for participants in youth sports is limited. Relative more emphasis is given to the talented few in contrast to the majority of youth participants. Individual differences are considerable and these are often dependent on the quality of coaching/instruction