Ahmed El-hadi | Umm Al-Qura University, Makkah, Saudi Arabia (original) (raw)

Papers by Ahmed El-hadi

PLLA is a thermoplastic biopolymer and can be used in industrial applications for medical and fil... more PLLA is a thermoplastic biopolymer and can be
used in industrial applications for medical and filtration
applications. The brittleness of PLLA is attributed to slow
crystallization rates and its glass transition temperature
(Tg) is high (60 °C); for this reason, its applications are
limited. The orientation, morphology, and crystal structure
of the electrospun fibers was investigated by SEM, POM,
DSC, FTIR, XRD, and SAXS. Combining with additives
leads to a large decrease of fiber diameter, viscosity, and
changes of fiber morphology and crystal structure compared
to pure PLLA. DSC showed that the Tg of PLLA
decreased about 15 °C and there was no change in relaxation
enthalpy by the addition of plasticizer. FT-IR indicate
a strong interaction between PLLA and additives; a new
band appears in the PLLA blend at 1,756 cm−1 at room
temperature as a crystalline band without any annealing. In
addition, WAXD indicated that the intensities of the two
peaks at (200/110) and (203) increased for the blend at
room temperature without any annealing in comparison
with PLLA; this means that PHB crystallizes in the amorphous
region of PLLA. The POM experiments agree with
the results from DSC, FTIR, and WAXS measurements,
confirming that adding PHB results in an increase in the
number of nuclei with much smaller spherulites and
enhances the crystallization behavior of this material,
thereby improving its potential for applications.

Biopolymer composites were prepared from poly (3-hydroxybutyrate) (PHB)/microcrystalline cellulos... more Biopolymer composites were prepared from poly
(3-hydroxybutyrate) (PHB)/microcrystalline cellulose fiber
(MCCF)/plastiziers/poly(vinyl acetate) by melt extrusion.
The morphology, crystal structure, and non-isothermal crystallization of these composites were investigated by polarized optical microscopy (POM), differential scanning
calorimetry, Fourier transform infrared spectrometer, and
wide-angle X-ray diffraction. The results of DSC indicate
that the addition of small amount of MCCF improved the
crystallization rate. Non-isothermal crystallization shows
that the composites 1 and 2 have lower crystallization half
time (t0.5) than that of pure PHB. Higher MCCF contents in
PHB (composite 4) lead to a decrease in the crystallization
rate. POM micrographs show that the MCCF were well
dispersed in the PHB matrix and served as a nucleating
agent with a strong change in PHB morphology. Increasing
the isothermal crystallization temperature above 120 °C,
leads to the formation of banded spherulites with large
regular band spacing. Decreasing the isothermal crystallization
temperature below 100 °C produces more and small
spherulites.

Poly lactic acid (PLLA) is a promising biopolymer, obtained from polymerization of lactic acid th... more Poly lactic acid (PLLA) is a promising biopolymer, obtained from polymerization of lactic acid that is derived from renewable resources through fermentation. The characteristic brittleness of PLLA is attributed to slow crystallization rates, which results in the formation of the large spherulites. Its glass temperature is relative high, above room temperature and close to 60 °C, and therefore its applications are limited. The additives poly((R)-3-hydroxybutyrate) (PHB), poly(vinyl acetate) (PVAc) and tributyl citrate (TBC) were used as compatibilizers in the
biodegradable polymer blend of (PLLA/PPC). Results from DSC and POM analysis indicated that the blends of PLLA
and PPC are immiscible. However, the blends with additives are miscible. TBC as plasticizer was added to PLLA to
reduce its Tg. PVAc was used as compatibilizer to improve the miscibility between PLLA and PPC. FT-IR showed
about 7 cm–1 shift in the C=O peak in miscible blends due to physical interactions. POM experiments together with the
results of DSC and WAXD showed that PHB enhances the crystallization behavior of PLLA by acting as bio nuclei
and the crystallization process can occur more quickly. Consequently an increase was observed in the peak intensity
in WAXD.

PHB is a thermoplastic biopolymer produced by fermentation ofrenewable resources. Secondary cryst... more PHB is a thermoplastic biopolymer produced by fermentation ofrenewable resources. Secondary crystallization during storage leading to an increased degree of crystallinity is a principal reason of PHB brittleness. In addition,
pure PHB has no residues of catalysts, meaning low nucleation density and slow crystallization rates, leading to the formation of large spherulites with cracks and brittleness. To overcome the brittleness of PHB, polymer composites based on PHB,
plasticizers, and nano-clays A and B were prepared by solvent casting. The addition of plasticizer decreases Tg from 5 to -13 C in all composites. Furthermore, the addition of nano-clays acts as a nucleating agent to PHB. The effect of nano-clays A
and B on spherulites morphology, thermal behavior, and crystal structure of PHB
composites were tested by several techniques. Differential scanning calorimetry analysis shows that the addition of nano-clay A does not change the crystallization temperature and the crystallization half-time (t1/2) of the PHB matrix but that nanoclay B accelerates the crystallization process. Thermogravimetric analysis revealed an increase in thermal stability of composites containing nano-clay B. Polarized
optical microscopy showed that nano-clays serve as nucleating agents in PHB matrix. Therefore, the spherulites become smaller and the nuclei density increases at the selected crystallization temperature

Spherulitic morphology of pure poly lactic acid (PLLA) PLLA have investigated after thermal annea... more Spherulitic morphology of pure poly lactic acid (PLLA) PLLA have investigated after thermal annealing. The morphology
of spherulite of pure poly lactic acid (PLLA) PLLA have investigated after thermal annealing. The effect of both
annealing temperature and crystallization temperature on the formation of cracks was described by polarized optical
microscope (POM). Non banded spherulite (fibrils) with cracks was detected in PLLA film after annealing at 160°C
(180 min.) and isothermal crystallization temperatures at 140°C and 150°C. With increasing temperature after annealing
treatment the size of spherulite is increased and more cracks are formed. The maximum growth rate of spherulites
was found at 130°C. The physical ageing was carried out by annealing the PLLA sample at room temperature for several
annealing time (ta) from 0 h to 720 h. The enthalpy relaxation has been studied by differential scanning calorimetry
(DSC) through analysis of the endothermic peak of glass transition temperature, which increased and shifted towards
higher temperature as the annealing time increased.

Bacterial thermoplastic polyesters poly (3-hydroxyalkanoate) PHAs are produced by the fermentatio... more Bacterial thermoplastic polyesters poly (3-hydroxyalkanoate) PHAs are produced by the fermentation of renewable
materials, such as sugars or molasses. The pure homopolymer, PHB, and pure copolymer (3-HBP-CO-HV) (88:12) are
brittle materials. PHB or PHB/V are mixed with other biodegradable materials to improve their mechanical properties.
The aim is to develop biodegradable polymers of PHB-base with improved mechanical properties, such as fracture
stress (27–18 MPa), strain (400–660%), impact strength and long-term stability, and to compare them with PE, PP and
PET. When nucleating agents are added, smaller spherulites are formed, thus improving the mechanical properties. The
mechanical properties of PHB and its blends are related to processing conditions, morphology, crystallinity and glass
transition. The blends are ductile polymers with plastic deformation (necking). They are biodegraded in aerobic tests,
under compost conditions in soil and water, and many pores are to be found on the surface. The blends are degraded
more easily in the aerobic test, i.e. in the river water and compost, than in the soil.

Poly(3-hydroxybutyrate) (PHB) is sensitive to high processing temperatures. This leads to a decre... more Poly(3-hydroxybutyrate) (PHB) is sensitive
to high processing temperatures. This leads to a decrease
in molar mass as well as a lower melt viscosity. The crystallization
temperature shifts to lower values, and crystallization
kinetics is slow. A mixture was developed in
order to improve the manufacturing properties and the
final product. The blends exhibit a slight reduction in
molar mass because they have a lower melting point than
pure PHB, and can be extruded at their melt temperature
of 170 to 1808C. Then they immediately crystallize at 125
to 1008C. Differential scanning calorimetry (DSC) shows
the effect of holding time in the melt on crystallization
behavior. It has been shown that the crystallization time
has to be longer in the case of PHB and shorter for the
blends. Thermal degradation of PHB and its blends has
been investigated using thermogravimetry analysis (TG).
Derivative thermogravimetry coupled with TG (TG/DTG)
curves show three decomposition stages for blends at 290,
340 and 4458C, respectively. Acetic acid, water, carbon
dioxide and methane are produced by degradation at a
higher temperature.