This work is focused on the preparation of new environmentally friendly hydrogels derived from cellulose and hence originating from renewable resources and characterized by biodegradable properties. Two cellulose derivatives, sodium carboxymethylcellulose (CMCNa) and hydroxyethylcellulose (HEC), were used for superabsorbent hydrogel preparation. Citric acid (CA), a crosslinking agent able to overcome toxicity and costs associated with other crosslinking reagents, was selected in a heat activated reaction. Differential scanning calorimeter (DSC), fourier transform infrared spectroscopy (FTIR), and swelling measurements were performed during the reaction progress to investigate the CA reactivity with each of the polymers. Also, CMCNa/HEC polymer mixtures (3/1 w/ w) crosslinked with CA were investigated and compared with previous results. Finally, a possible reaction mechanism was proposed.

The effects of temperature, strain rate and filler content on tensile properties of SAN/glass bead composites are studied. A point of discontinuity on the stress‐strain curves for unannealed composites is investigated, annealing results in smooth curves with no discontinuities. A simple model for the filler effect on yield stress is suggested and shown to be in a good agreement with experimental data. A double shifting procedure to account for the temperature and filler effects on yield stress as a function of strain rate is proposed. A single master curve that can be represented by the equation: relates composite yield stress to strain rate, temperature and filler volume fraction.

In this study, polymer nanocomposites based on poly(lactic acid) (PLA) and organically modified layered silicates (organoclay) were prepared by melt mixing in an internal mixer. The exfoliation of organoclay could be attributed to the interaction between the organoclay and PLA molecules and shearing force during mixing. The exfoliated organoclay layers acted as nucleating agents at low content and as the organoclay content increased they became physical hindrance to the chain mobility of PLA. The thermal dynamic mechanical moduli of nanocomposites were also improved by the exfoliation of organoclay; however, the improvement was reduced at high organoclay content. The dynamic rheological studies show that the nanocomposites have higher viscosity and more pronounced elastic properties than pure PLA. Both storage and loss moduli increased with silicate loading at all frequencies and showed nonterminal behavior at low frequencies. The nanocomposites and PLA were then foamed by using the mixture of CO 2 and N 2 as blowing agent in a batch foaming process. Compared with PLA foam, the nanocomposite foams exhibited reduced cell size and increased cell density at very low organoclay content. With the increase of organoclay content, the cell size was decreased and both cell density and foam density were increased.

Isothermal melt crystallization of poly( L-lactide ) (PLLA) has been studied in the temperature range of 90 to 135ЊC. A maximum in crystallization kinetic was observed around 105ЊC. A transition from regime II to regime III is present around 115ЊC. The crystal morphology is a function of the degree of undercooling. At crystallization temperatures (T c ) below 105ЊC, further crystallization occurs upon heating; this behavior is not detected for T c above 110ЊC. The analysis of the heat capacity increment at glass transition temperature ( T g ) and of dielectric properties of PLLA indicates the presence of a fraction of the amorphous phase which does not relax at the T g , and the amount of this so-called rigid amorphous phase is a function of T c .