This paper presents results from an experimental study on the static and dynamic mechanical and viscoelastic properties of short hemp fibre polypropylene composites. Composites containing 10–60 wt.% short noil hemp fibre were injection moulded. The maleic anhydride grafted polypropylene (MAPP) and maleic anhydride grafted Poly(ethylene octane) (MAPOE) were used as coupling agents for modifying the matrices. Dynamic mechanical thermal analysis (DMTA) of the composites were performed over a temperature range of 25–150°C under frequency of 1 Hz. DMTA revealed no noticeable changes in α-transition temperature when the fibre content was increased or coupling agents were added. The composites revealed better temperature resistance at higher fibre content. However, the increase in storage modulus was negligible in composites reinforced with more than 40 wt.% hemp fibres; due to the agglomeration of the fibres. The results of the damping ratio analysis revealed that higher interfacial bonding was achieved by addition of MAPP coupling agent in comparison with addition of MAPOE coupling agent. This was also confirmed by tensile strength experiments and scanning electron microscope (SEM) observations.

The study of fibre/matrix bond strength in short hemp polypropylene composites from dynamic mechanical analysis

Bioplastics with a wide range of mechanical properties were directly obtained from industrially processed edible vegetable and cereal wastes. As model systems, we present bioplastics synthesized from wastes of parsley and spinach stems, rice hulls, and cocoa pod husks by digesting in trifluoroacetic acid (TFA), casting, and evaporation. In this way, amorphous cellulose-based plastics are formed. Moreover, many other natural elements present in these plants are carried over into the bioplastics rendering them with many exceptional thermo-physical properties. Here, we show that, due to their broad compatibility with cellulose, amorphous cellulose can be naturally plasticized with these bioplastics by simply mixing during processing. Comparison of their mechanical properties with that of various petroleum based synthetic polymers indicates that these bioplastics have equivalent mechanical properties to the nondegrading ones. This opens up possibilities for replacing some of the nondegrading polymers with the...

Direct Transformation of Edible Vegetable Waste into Bioplastics

Increased functional properties and thermal stability of flexible cellulose nanocrystal/ZnO films

In this project, free vibration testing and dynamic mechanical analysis methods were used to study the damping properties of noil hemp fibre-reinforced polypropylene composites with varying fibre contents (0 to 60 wt%) and compatibilizers (maleic anhydride-grafted polypropylene and maleic anhydride-grafted polyethylene octane) under applied frequencies of 1 to 200 Hz. The storage modulus of the composites was increased by the increase in hemp fibre content.
However, the maximum damping ratio was obtained from the composite with 30 wt% noil hemp fibre. The addition of coupling agents reduced the damping capacity of all composites. However, 30 wt% noil hemp fibre-reinforced polypropylene coupled with 2.5 wt% anhydride-grafted poly ethylene octane revealed the highest damping ratio among coupled composites. Damping properties of the composites were relatively constant over the frequency range, except at frequencies which the material–instrument system began to resonate and peaks were observed in the curves.

Vibration damping characteristics of short hemp fibre thermoplastic composites

Nanoporous cellulose nanocomposite foams as high insulated food packaging materials

The molecular dynamics in hydrated cellulose has been investigated by a combination of thermal analyses and dielectric spectroscopy. Differential scanning calorimetry shows the dependence upon hydration of the glass transition temperature Tg. A physical ageing phenomenon has been observed. At the molecular scale, bound water is hydrogen bonded to polar sites of cellulose macromolecules. At the macroscopic scale, water molecules play the role of a plasticizer for cellulose lowering its Tg. Dynamic dielectric spectroscopy combined with thermostimulated currents have allowed us to follow more localized molecular mobility. The β relaxation mode is characterized by activation entropies that vanish for higher water contents indicating molecular mobility localization. It is plasticized by water like the glass transition. This analogy is explained by a common origin of both mechanisms: the mobility of the cellulose backbone. The evolution of the γ mode upon hydration follows an anti-compensation law. Water acts as an anti-plasticizer in a hydrogen bonded network.

/pdf/influence-of-hydrogen-bonds-on-glass-transition-and-5dr4xyq00o.pdf

Influence of hydrogen bonds on glass transition and dielectric relaxations of cellulose

The influence of hydration on cellulose molecular mobility is investigated by two dielectric methods at different molecular scale. The mobility of side groups, assigned to γ mode, for dried cellulose increases. The water molecules have an anti-plasticizer effect on γ mode due to the water–polymer hydrogen bonding. For the β relaxation mode, only observed by the Thermo Stimulated Current technique, the hydration plays a role of plasticizer. The α relaxation mode assigned to the delocalized cooperative mobility of long chain segments of cellulose is plasticized by water. The study of activated parameters deduced from fractional polarization procedure, shows an increase of the activation enthalpy range with dehydration. It permits to conclude that reduction of hydrogen bonds density leading to a more extended cooperative mobility.

Influence of water on localized and delocalized molecular mobility of cellulose

The low-temperature molecular mobility of three different wood species was analyzed, with the two major constituents—cellulose and lignin—as reference. Mechanical and dielectric dynamic techniques were used. In order to observe the fine structure of the broad relaxation modes of wood, a very low-frequency analysis was carried out by thermostimulated current technique. Low-temperature relaxations of rosewood were assigned to low-temperature relaxations of cellulose. There was no dielectric response of lignin in rosewood. Contrarily, both cellulose and lignin responses were distinguished in ebony and varongy. Thermostimulated currents analyses exhibit the specific behavior of lignin in the various wood species. Moreover, the relaxation mode of cellulose observed at lower temperature remains localized in rosewood, while it tends to delocalize in varongy and ebony. The nature and intensity of physical interactions that induce variation of phase miscibility might be responsible for the observed differences. Even at the scale of the c relaxation, physical interactions modify molecular mobility.

/pdf/dielectric-and-mechanical-properties-of-various-species-of-3g8r9lhn3m.pdf

Dielectric and mechanical properties of various species of Madagascan woods

Arabidopsis Thaliana is a plant composed mainly of cellulose and lignin. Geneticists need techniques able to make differences at the molecular level between modified plants (DML6, CAD C/D) and non-modified ones. Thermo-stimulated current (TSC) analysis is a promising route to identify gene mutations. For the non-modified plant, at low temperatures, TSC thermograms highlight three dielectric relaxation modes. From −150 to −110 °C, γCellulose is attributed to CH2OH and–OH groups of cellulose. Between −110 and −80 °C, βLignin is detected. From −80 to −40 °C, βCellulose is characteristic of the molecular mobility of glycosidic linkages. For the CAD C/D modified plants, only γCellulose and βLignin are observed; due to analogous enthalpy values, those modes have the same molecular origin as in the non-modified plant. So, the βLignin mode is associated with the molecular mobility of the lignin-OH groups. The CAD C/D gene mutation changes the chemical structure of lignin, which promotes hydrogen bonds in the network and inhibits molecular mobility of glucosidic rings. It is also interesting to note that the DML6 gene mutation induces a higher cooperativity of this βCellulose relaxation than in wild vegetal composites. In fact, this mutation promotes molecular mobility of glycosidic rings thanks to β1–4 glycosidic linkages.

http://iopscience.iop.org/article/10.1088/0022-3727/45/29/295402/pdf

Analysis of gene mutation in plant cell wall by dielectric relaxation

Thanks to mutant CAD C/D, β Lignine mode has been associated with the molecular mobility of lignin polar groups (-OH). In this mutant, the genetic modification changes the chemical structure of lignin and increases the proportion of hydroxyl groups. The increase of hydroxyl groups ratio promotes hydrogen bonds which inhibits molecular mobility of glucosidic rings. Thermo Stimulated Current is suitable to identify the influence of gene mutation on the physical structure of the natural plant. The evolution of mobility is clearly exhibited.

Frédéric Roig

Papers

Influence of hydrogen bonds on glass transition and dielectric relaxations of cellulose

Influence of water on localized and delocalized molecular mobility of cellulose

Dielectric and mechanical properties of various species of Madagascan woods

Analysis of gene mutation in plant cell wall by dielectric relaxation

Thermo Stimulated Currents a method to identify gene mutation in Arabidopsis Thaliana