Mustapha Kaci

Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate)/Polylactide Blends: Thermal Stability, Flammability and Thermo-Mechanical Behavior

Blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polylactide (PLA) with different PHBV/PLA weight ratios (100/0, 75/25, 50/50, 25/75, 0/100) were prepared by melt compounding. Their mutual contributions in terms of thermal stability, flammability resistance, mechanical properties and rheological behavior were investigated. The study showed that the increase in PLA content in PHBV/PLA blends leads to enhanced properties. Consequently, thermal stability and flammability resistance were improved. Further, the rheological measurements indicated an increase in storage modulus and loss modulus of PHBV matrix by addition of PLA.

Crystallinity Measurements of Unstabilized and HALS-stabilized LDPE Films Exposed to Natural Weathering by FT-IR, DSC and WAXS Analyses

Abstract The crystallinity of unstabilized low-density polyethylene (LDPE) films and those stabilized with hindered-amine light stabilizers (HALS) was studied under natural weathering conditions, up to 170 and 650 days, respectively. The HALS tested was Tinuvin 783, added to the polymer in the concentration of 0.6% (wt/wt). The crystallinity changes were evaluated by means of Fourier-Transform Infrared (FT-IR) spectroscopy, wide-angle. X-ray scattering (WAXS), and Differential scanning calorimetry (DSC). The comparison of the results obtained by FTIR and WAXS confirmed the accuracy of using the rocking bands 730 and 722cm−1. The trends of the crystallinity measured by DSC were different from those determined by FT-IR and WAXS.

Recyclability of Polystyrene/Clay Nanocomposites

PS/organo-modified clay (5% w/w) nanocomposite has been subjected to a series of eight processing cycles in a twin screw extruder. The influence of multiple recycling on the properties of the nanocomposite was studied by following the changes in the morphology, the molecular structure, the melt flow index (MFI) and the thermal properties. The WAXS results indicate a strong intercalation of PS chains between silicate layers of the organoclay and the extent of intercalation appears to increase with increasing the number of cycles. The main effects of recycling are a reduction in molecular weight due to chain scission, although the occurrence of a crosslinking fraction is probable after 8 cycles. The thermal properties remain almost stable during reprocessing.

Mechanical Recycling of Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate)/Polylactide Based Blends

The effects of recycling cycles (up to six repeated cycles) on the structure and properties of neat poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), neat polylactide (PLA) and PHBV/PLA: 50/50 (wt%) blends elaborated by melt molding process were investigated. The changes in the chemical structure, the morphology and the thermal, mechanical and rheological properties of the recycled materials were studied. The reduction of molecular weights of both PHBV and PLA showed the predominance of chain scission mechanism as a result of degradation inducing an enhancement of PHBV chain mobility, as also revealed by the increasing of the PHBV crystallinity measured using differential scanning calorimetry and wide angle X-ray scattering. Nevertheless, all these effects were significantly smaller for neat PLA and PHBV–PLA blends compared to those of neat PHBV. Contrary to PLA, PHBV seems to be relatively more sensitive to the thermomechanical degradation and the presence of PLA in the PHBV–PLA blend tends to partially prevent the degradation of PHBV. Mechanical results evidenced the great recyclability of PHBV/PLA blends, even after six reprocessing cycles, since the values of mechanical characteristics remain more or less constant compared to the initial ones revealing the preservation of the material mechanical properties. A stabilizing effect of PLA on the recyclability of PHBV–PLA blends was highlighted and it can be concluded that the incorporation of PLA in PHBV/PLA blends might be a promising route to extend the PHBV applications.

Characterization by Chemiluminescence of Unstabilized and HALS-Stabilized LDPE Films Exposed to Natural Weathering Conditions

ABSTRACT Photostability of low-density polyethylene (LDPE) films under natural weathering conditions was investigated in the absence and the presence of various structures of hindered amine light stabilizers (HALS) by chemiluminescence (CL) and Fourier transform infrared (FTIR) spectroscopy. The stabilizers studied were Sanduvor PR 31 (as grafted HALS) and Uvasil 299 and Tinuvin 123 (as non-grafted HALS). The HALS were added separately to LDPE at the same concentration, namely 0.3% (w/w). It was found that the weathered stabilized samples exhibited a relative long period during which the CL signal slowly increased, while for unstabilized samples, CL increased after a short induction period. This behavior could be explained by reduction in the rate of hydroperoxide decomposition caused by nitroxyl radicals. However, the very high increase in stability observed in the case of Sanduvor PR 31 sample could be assigned to the grafting effect of the HALS on the polymer chain. At longer exposure times, the oxidation induction time decreased slowly as a result of stabilizer consumption in the photooxidative process. These changes in CL parameters were found to correlate with carbonyl index determined by FTIR spectroscopy.

The effects of PHBV-g-MA compatibilizer on morphology and properties of poly(3-hydroxybutyrate-Co-3-hydroxyvalerate)/olive husk flour composites

Abstract The paper provides some experimental data on the effects of a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) grafted maleic anhydride (PHBV-g-MA) used as the compatibilizer for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/olive husk flour (OHF) composites prepared by melt compounding. The natural filler was added to PHBV at various contents, i.e. 10, 20, and 30 wt%, while the amount of PHBV-g-MA was 5 wt% based on neat PHBV. Morphology, contact angle measurements, water absorption (WA), mechanical, viscoelastic, and barrier properties of the various composites were investigated with and without the compatibilizer. The study showed through scanning electron microscopy that the addition of PHBV-g-MA to PHBV/OHF composites resulted in better and finer dispersion of the filler in the matrix, even at a higher content ratio, indicating improved affinity between the components. This is in agreement with the decrease in both surface energy and WA. Furthermore, tensile and dynamic mechanical measurements indicated a reinforcing effect of OHF in PHBV composites, being more pronounced in the presence of PHBV-g-MA. The barrier properties against oxygen and water vapor were also improved for the compatibilized composites.

Effect of hydrothermic ageing on dielectric and mechanical properties of rigid poly(vinyl chloride)

An accelerated hydrothermic ageing (according to N.F.T. 54043 method) was performed on samples of rigid poly(vinyl chloride). The test consisted of sample immersion in boiling wate at 100°C for different exposure periods up to 480 h. The samples were removed from the boiling water every two hours for mechanical and dielectric characterization and color test. The dielectric measurements carried out on aged samples, up to 40 h, showed that the permittivity remained almost constant and its value was found to be 2.3 in the range - 100 to +62.8°C. However, as the temperature approaches the glass transition (T g =88.3°C), the permittivity was observed to increase rapidly. It was also found that the permittivity of aged samples was lower than that of the non-aged samples. The dielectric loss factor (tan δ) measurements with respect to temperature have confirmed the presence of two relaxations : β at low temperature (around -35°C) and α near the T g . The combined action of water and temperature reduced the intensity of the corresponding relaxation peaks. The sample color index was evaluated up to 480 h using the SYNMERO scale in order to estimate the degradation extent. Unexpectedly, elongation at break under uniaxal traction remained unaffected by the hydrothermic ageing, meaning that two competing processes were involved simultaneously (sample degradation via chain scission and sample plastification via water absorption).

Effect of Algerian Halloysite on the Mechanical and Thermal Properties of Starch-Grafted-Polyethylene Nanocomposites

This paper deals with the characterization of the physico-mechanical properties of starch-grafted-polyethylene (Starch-g-PE)/unmodified Algerian halloysite nanotubes (HNT) nanocomposites prepared by melt compounding. The nanoclay was incorporated at various filler contents, i.e., 1.5, 3 and 5 wt%. Rheological and tensile properties of the nanocomposites were evaluated by different techniques and the results obtained are compared with those of virgin Starch-g-PE matrix. The study shows a decrease in melt flow index (MFI) values upon increasing the HNT content, which indicates a restriction in the polymer chains mobility due to the confinement effect of HNT. Further, a tensile strength is also improved.

Tribological and mechanical properties of polyamide-11/halloysite nanotube nanocomposites

Abstract This article reports some morphological, tribological, and mechanical data on polyamide-11(PA11)/halloysite nanotube (HNT) nanocomposites prepared by melt-compounding. HNTs extracted from the Djebel Debbagh deposit in Algeria were incorporated into the polymer at 1, 3, and 5 wt%. For comparison, commercial HNTs were also used under the same processing conditions. Scanning electron microscopy showed that both HNTs were homogeneously dispersed in the PA11 matrix, despite the presence of few aggregates, in particular at higher filler contents. The tribological properties were significantly improved, resulting in a decrease in the friction coefficient and the wear rate characteristics due to the lubricating effect of HNTs. This is consistent with optical profilometry data, which evidenced the impact of both types of HNTs on the surface topography of the nanocomposite samples, in which the main wear process was plastic deformation. Furthermore, Young’s modulus and tensile strength were observed to increase with the filler content, but to the detriment of elongation at break and impact strength. Regarding the whole data, the raw Algerian halloysite led to interesting results in PA11 nanocomposites, thus revealing its potential in polymer engineering nanotechnology.

The Effects of Accelerated Photooxidation on Molecular Weight and Thermal and Mechanical Properties of PHBV/Cloisite 30B Bionanocomposites

The effects of accelerated photooxidation on the molecular weight and thermal and mechanical properties of Cast PHBV and PHBV/Cloisite 30B (3 wt%) bionanocomposites are investigated herein. Through size exclusion chromatography (SEC) analysis, a significant decrease in both weight and number average molecular weights was observed for all irradiated samples over time, resulting from the chain scission mechanism. Differential scanning calorimetry (DSC) data indicated a decrease in degree of crystallinity and melting temperature after UV exposure, with the appearance of double melting peaks related to the changes in the crystal structure of PHBV. Thermal stability, tensile and thermo-mechanical properties were also reduced consecutively in photooxidation, being more pronounced for Cast PHBV. This study shows that the incorporation of Cloisite 30B in PHBV provides a better resistance to photooxidation in comparison with the neat polymer.