The degree of crystallinity of cellulose was used for assessing the degradation level of coated and uncoated samples of pine wood after weathering. X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy measured the changes in the surface crystallinity of cellulose resulting from weathering, both natural and artificial. Both techniques revealed an increase in the crystallinity index (CI) of cellulose when wood was subjected to weathering. An increase in the size of crystallites was also observed by XRD measurements. These results were related to the reduction of the amorphous fractions of wood, and, consequently, to the enrichment of the relative crystalline content. Thanks to FT-IR analysis, the degradation of hemicellulose was observed for uncoated samples after exposure to artificial weathering. The effect of weathering was less evident on coated samples because of the protective action of the coating. A good correlation between the crystallinity indexes obtained from FT-IR and XRD was found. The experimental results proved that the proposed method may be a very useful tool for a rapid and accurate estimation of the degradation level of wood exposed to weathering. This methodology can find application in the field of conservation and restoration of wooden objects or in the industry of wood coatings.

Abstract:The propagation of low intensity ultrasound in a curing resin, acting as a high frequency oscillatory excitation, has been recently proposed as an ultrasonic dynamic mechanical analysis (UDMA) for cure monitoring. The technique measures sound velocity and attenuation, which are very sensitive to changes in the viscoelastic characteristics of the curing resin, since the velocity is related to the resin storage modulus and density, while the attenuation is related to the energy dissipation and scattering in the curing resin. The paper reviews the results obtained by the authors' research group in the last decade by means of in-house made ultrasonic set-ups for both contact and air-coupled ultrasonic experiments. The basics of the ultrasonic wave propagation in polymers and examples of measurements of the time-evolution of ultrasonic longitudinal modulus and chemical conversion of different thermosetting resins are presented. The effect of temperature on the cure kinetics, the comparison with rheological, low frequency dynamic mechanical and calorimetric results, and the correlation between ultrasonic modulus and crosslinking density will be also discussed. The paper highlights the reliability of ultrasonic wave propagation for monitoring the physical changes taking place during curing and the potential for online monitoring during polymer and polymer matrix composite processing.

No abstract

No abstract

The propagation of low-intensity ultrasound in polymers, acting as a high-frequency dynamic mechanical deformation, can be successfully used to monitor changes in the modulus of polymers associated with glass transition, crystallization, cross-linking, and other chemical and physical phenomena related to changes in the viscoelastic behavior, such as gelation phenomena. The velocity of sound is related to the polymer storage modulus and density, whereas the absorption of ultrasonic waves is related to the energy dissipation in the material and, therefore, to the loss modulus. Accordingly, ultrasonic measurements have been used by several authors to monitor the evolution of the viscoelastic moduli of polymers as a function of time or temperature and, recently, become a characterization technique of its own right, generally known as ultrasonic dynamic mechanical analysis (UDMA). Often the technique is used in conjunction with rheological methods as a means of providing a better insight into the viscoelastic behavior of polymer systems. As yet UDMA is underutilized primarily because of the low operating temperatures (usually below 100 • C) of commercially available ultrasonic transducers, and also due to the requirement of a coupling medium to ensure an efficient energy transfer mechanism between the transducer and the test material. Despite these limitations, this paper shows that the use of ultrasonics is potentially a powerful method for the characterization of polymers, particularly as a tool for online monitoring of events occurring during polymer processing and in the manufacture of polymer matrix composites. The aim of this paper is to review the progress made in recent years, highlighting the potential and reliability of UDMA for monitoring physical transitions in polymers such as glass transition, melting, crystallization, as well as physical

No abstract

No abstract

Fish waste is attracting growing interest as a new raw material for biopolymer production in different application fields, mainly in food packaging, with significant economic and environmental advantages. This review paper summarizes the recent advances in the valorization of fish waste for the preparation of biopolymers for food packaging applications. The issues related to fishery industry waste and fish by-catch and the potential for re-using these by-products in a circular economy approach have been presented in detail. Then, all the biopolymer typologies derived from fish waste with potential applications in food packaging, such as muscle proteins, collagen, gelatin, chitin/chitosan, have been described. For each of them, the recent applications in food packaging, in the last five years, have been overviewed with an emphasis on smart packaging applications. Despite the huge industrial potential of fish industry by-products, most of the reviewed applications are still at lab-scale. Therefore, the technological challenges for a reliable exploitation and recovery of several potentially valuable molecules and the strategies to improve the barrier, mechanical and thermal performance of each kind of biopolymer have been analyzed.