All issues / Volume 4 (2010) / Issue 7 (July)
To promote dispersion of nano-silica in monomer casting nylon6 (MC nylon6), nano-silica was dispersed in melted caprolactam with the assistance of ultrasound, anionic polymerization was then initiated to form silica/MC nylon6 in-situ nanocomposites. It was found that hydrogen bonds were formed between nano-silica and caprolactam, in the meantime, ultrasound helped to break the nanoparticles aggregations into smaller ones or even mono-dispersing particles. Therefore, the agglomerated nanoparticles were pulled apart and stabilized by caprolactam. Additionally, the rapid anionic polymerization of caprolactam also contributed to the avoidance of re-agglomeration and deposition of nanoparticles during the polymerization process, leading to the uniform distribution of nanoparticles in the polymer matrix. Mechanical tests indicated that the silica/MC nylon6 in-situ nanocomposites prepared according to the above strategy were simultaneously toughened, strengthened and stiffened. Thermogravimetric analysis (TGA) results showed that thermal stability of nanocomposites was notably improved compared to neat MC nylon6.
The composite material based on poly(butylene succinate) (PBS), poly(butylene adipate-co-terephthalate) (PBAT) and organo-modified montmorillonite (OMMT) were prepared by melt blending technique and characterized. Sodium montmorillonite (Na-MMT) was successfully modified by octadecylammonium (ODA) and dimethyldioctadecylammonium (DDOA) salts to become OMMT through cation exchange technique which is shown by the increase of basal spacing of clay by XRD. The addition of the OMMT to the PBS/PBAT blends produced nanocomposites which is proved by XRD and TEM. Tensile tests showed increase in tensile strength and modulus which is attributed to the existence of strong interactions between PBS/PBAT and clay, particularly with OMMT. Highest tensile strength of nanocomposite was observed at 1 wt% of OMMT incorporated. TGA study showed that the thermal stability of the blend increased after the addition of clays. SEM micrographs of the fracture surfaces show that the morphology of the blend becomes homogeneous and smoother with presence of OMMT.
Synthesis and characterizations of degradable aliphatic-aromatic copolyesters from lactic acid, dimethyl terephthalate and diol: Effects of diol type and monomer feed ratio
M. Namkajorn, A. Petchsuk, M. Opaprakasit, P. Opaprakasit
Vol. 4., No.7., Pages 415-422, 2010
Vol. 4., No.7., Pages 415-422, 2010
Lactic acid-based aliphatic/aromatic copolyesters are synthesized to incorporate the degradability of polylactic acid and good mechanical properties of aromatic species by using polycondensation of lactic acid (LA), dimethyl terephthalate (DMT), and various diols. Effects of diol lengths and comonomer feed ratios on structure and properties of the resulting copolymers are investigated. Three types of diols with different methylene lengths are employed, i.e., ethylene glycol (EG), 1,3-propanediol (PD) and 1,4-butanediol (BD). LA/DMT/diol feed ratios of 2:1:2, 1:1:2, and 1:2:4 are used in each diol system. It is found that types of the diols play an important role in the properties of the copolyester, where an increase in diol length results in an increase in the copolymers molecular weight, and a decrease in Tg, Tm and crystallinity, when a constant monomer feed ratio is employed. Monomer feed ratio also has a significant effect on properties of the copolymers, where an increase in the aromatic content leads to formation of copolymers with higher molecular weight, longer aromatic block sequence and high aromatic to aliphatic ratio in the chain structure. These, in turn, lead to an increase in Tg, Tm, crystallinity and thermal stability of the copolymer samples, and a reduction in their solubility.
Woven and nonwoven flax fiber reinforced poly lactic acid (PLA) biocomposites were prepared with amphiphilic additives as accelerator for biodegradation. The prepared composites were buried in farmland soil for biodegradability studies. Loss in weight of the biodegraded composite samples was determined at different time intervals. The surface morphology of the biodegraded composites was studied with scanning electron microscope (SEM). Results indicated that in presence of mandelic acid, the composites showed accelerated biodegradation with 20–25% loss in weight after 50–60 days. On the other hand, in presence of dicumyl peroxide (as additive), biodegradation of the composites was relatively slow as confirmed by only 5–10% loss in weight even after 80–90 days. This was further confirmed by surface morphology of the biodegraded composites. We have attempted to show that depending on the end uses, we can add different amphiphilic additives for delayed or accelerated biodegradability. This work gives us the idea of biodegradation of materials from natural fiber reinforced PLA composites when discarded carelessly in the environment instead of proper waste disposal site.
Copolymers of racemic β-butyrolactone ((R,S)-BL) and ε-caprolactone (CL), were synthesized by ring-opening polymerization initiated by sodium hydride (NaH). The initiator exhibited a satisfactory catalytic activity, producing copolymers whose yields are greatly influenced by the feed monomer ratio, CL/BL. All polymers obtained were characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and wide angle X-rays scattering, WAXS. The molar composition of copolyesters determined by 1H-NMR spectra, showed that the incorporation of CL is favoured over the incorporation of (R,S)-BL. Gel permeation chromatography and 13C-NMR spectra indicated that CL/BL copolymers had block sequence distribution. The TGA analysis of copolymers showed that these copolymers are stable up to temperatures near 200°C, followed by a decomposition process in two steps; the first one is attributed to the (R,S)-BL block degradation and the second to the remaining PCL block. The crystallization process of these copolymers was studied by DSC and WAXS showing that the amorphous (R,S)-BL segments chains did not affect the crystallinity of the PCL blocks.
A novel engineering plastic polytridecamethylene 2,6-naphthalamide (PA13N) was prepared via a reaction of 2,6-naphthalene dicarboxylic acid and 1,13-tridecanediamine through a three-step procedure. The structure of synthesized PA13N was characterized by elemental analysis, Fourier transform infrared (FT-IR) spectroscopy and proton nuclear magnetic resonance (1H-NMR). The thermal behaviors were determined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The solubility, water-absorbing capacity, and mechanical properties of PA13N have also been investigated. Melting temperature (Tm), glass transition temperature (Tg) and decomposition temperature (Td) of PA13N are 288, 129 and 492°C, respectively. The results show that the heat resistance and mechanical properties of PA13N are near to those of polynonamethylene terephthalamide (PA9T), and PA13N is a promising heat-resistant and processable engineering plastic.
A novel reversible thermo-swelling gel was prepared from poly(vinyl alcohol)-trimellitate (PVA-T) by crosslinking with ethylene glycol diglycidyl ether (EGDGE). Only in the presence of sulfate anion, this polymer gel showed a significant and reversible swelling behavior with increasing the temperature from 5 to 40°C, and vice versa, probably due to the scission and formation of the inter- and/or intramolecular hydrogen-bondings (HBs) between the carboxyls on the side groups. The involvement of inter- and/or intramolecular HBs for the thermo-swelling behavior was also suggested by a significant dependence on HCl concentration of the swelling degree. In addition, the swelling reversibility and reproducibility were confirmed via the temperature jump between 5 and 40°C, well satisfying for a candidate as a thermosensitive material.