Nonisothermal melt crystallization of PHB/babassu compounds

Abstract

Poly(3-hydroxybutyrate) (PHB)/babassu compounds were prepared in a laboratory internal mixer with 10, 30, and 50 % by mass of fiber content. Nonisothermal melt crystallization behavior of PHB/babassu compounds was investigated using differential scanning calorimetry, and crystallization parameters were determined at cooling rates ranging between 2 and 32°C min -1 . Adding babassu fiber affected the melt crystallization behavior of PHB, and increasing filler content from 10 to 30 % has significant effects on the thermal characteristics of the system. Further increase in filler content from 30 to 50 % filler content has no effect on crystallization temperature and rate, but it has important positive consequences, once there is a considerably latitude in choosing the actual filler level in highly loaded PHB/babassu compounds without affecting processing characteristics. The melt crystallization kinetics of PHB/babassu compounds was analyzed by three empirical models widely used to represent nonisothermal polymer crystallization data: Pseudo-Avrami, Ozawa, and Mo. Kinetics analyses indicate that the Pseudo-Avrami model represented well the experimental data for both compounds in a wide interval of temperature, conversion, and cooling rates; the Ozawa model with two different sets of parameters, for low and high cooling rates, was found to correlate the data equally well, but over limited ranges of the variables, and the model proposed by Mo and collaborators did not adequately represent the experimental data for the systems and conditions tested. List of symbols cCrystallization rate c 0.1-99.9% Crystallization rate measured between 0.1 and 99.9 % of mass transformation c 20-80% Crystallization rate measured between 20 and 80 % of mass transformation c max Maximum crystallization rate (at T c ) E 0 Total latent heat released or absorbed by the sample during the crystallization or melting event F Mo rate parameter J DSC output heat flow rate of thermal energy exchanged between sample and the surroundings J 0 Virtual baseline during a phase change event K 0 Pseudo-Avrami rate parameter m Ozawa exponente MFR Melt flow rate M n Number average molar weight n 0 Pseudo-Avrami exponente t 1Onset time of the crystallization event t 2Endtime of the crystallization event T Temperature T 0.1% Temperature to attain 0.1 % of crystallized fraction T 50%

Effect of heat cycling on melting and crystallization of PHB/TiO2 compounds

“…Regarding the influence of the fillers, addition of babassu filler in higher concentrations (10 to 50 wt%) increased the crystallization peak temperature and crystallization rate; carbon black acted as a nucleating agent during PHB crystallization. The effect of ZnO on the PHB crystallization is unclear and strongly dependent on its concentration, behaving as an accelerator or an inhibitor upon changing of filler content [13][14][15][16] .…”

“…Few articles are concerned with PHB crystallization and melting behaviour in the presence of fillers. For instance carbon black (CB) and babassu natural fibers induce PHB partial crystallization from the melt during cooling and partial cold crystallization on reheating [13][14][15] . The amount of polymer crystallization in each stage depends strongly on the cooling rate and the filler content, being the melting subtly affected by the fillers and experiment rates.…”

Processing and Properties of PCL/Cotton Linter Compounds

“…Usually, biodegradable polymer as example PHB present complex peaks during fusion due to different morphologies, crystallite sizes and stabilities; however in the present work neither cotton linter nor cotton nanolinter changed the thermal character of PCL. Although the acid hydrolysis to which cotton linter was subjected with the intention of generating new reactive groups and chemical links between PCL and cotton nanolinter, seemingly it was not strong enough to create new populations of crystals [34][35][36] . Concerning the crystallization peak, it became narrower and sharper upon filling addition; this result suggests an increase in polymer homogeneity.…”

Polycaprolactone (PCL)/alumina and PCL/niobium pentoxide composites: Rheology, crystallization, and mechanical properties

“…However, at the rates of 16°C/min and 32°C/min, a moderate increase in the crystallization rate occurs with the increase of filler content, when compared to pure PCL. Vitorino et al also obtained an increase in the maximum crystallization rate for high cooling rates (12°C/min, 16°C/min, 24°C/min, and 32°C/min) for PHB/babassu composites with fiber content ranging from 10% to 50%.…”