دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و چهارم شماره 6 (پیاپی 116، بهمن و اسفند 1390)

Acopolymer of styrene and methyl styrene was synthesized by nitroxide - mediated “living” free radical polymerization (NMP). N-Bromosuccinimide was used as a brominating agent to obtain a copolymer with bromine as its end group. This brominated copolymer was used as macro initiators for atom transfer radical polymerization (ATRP). Chemical modification of the clay and transformation of this inorganic material to an organophilic clay was carried out by cation exchange reaction between the clay and hexadecyl trimethyl ammonium chloride salt in deionized water by mechanical stirring. Preparation of nanocomposite was carried out by solution intercalation method. The structures of the terpolymer and other compounds were investigated by 1H NMR, GPC, FTIR, SEM, TEM and XRD methods and their thermal stability was examined by TGA analyses.

Block copolymers and cetyltrimethylammonium bromide were used as templates in nano silica structure formation like MCM-41(Mobil Composition of Matter), SBA16 (Santa Barbara Amorphous) and a new compound namely SPB (silicone mesoporous particles, prepared by sol-gel method using PPG-PEGPPG block copolymer) to compare the porosity and regularity of the products together. In this work tetraethylorthosilicate (TEOS), as silica source and alcohol as surface modifying agent were used because of having the main advantage, compared to an ionic template such as cetyltrimethylammonium bromide, in producing larger pores and thicker walls for holding larger catalytic molecules in their pores or increasing their resistance towards fragmentation. In order to study the copolymer as a template, SPB structure was prepared and compared with SBA16 which was found to have broader pore-size distribution and smaller specific surface area. Using alcohol in particle production resulted in higher formation rate of micelles with improved morphology. Nitrogen adsorption-desorption, X-ray diffraction and electron scanning microscopy confirmed the mesoporous structure and regularity of these synthesized materials. Finally a mechanism is proposed for the formation of these structures.

Cellulose nanocrystal (CNC) is a type of nanomaterial which is produced by partial hydrolysis of cellulose and elimination of its amorphous regions. CNC has several advantages such as biodegradability and safety toward human health. In this study, CNC was produced from cotton linters and methods such as transmission electron microscopy and atomic force microscopy were used for confirmation of nanoscale size production of cellulose crystals. Carboxymethyl cellulose (CMC)/polyvinyl alcohol (PVA)-nanoclay (MMT) and CMC-PVA-CNC films, containing 3-10% (wt/wt CMC) nanofillers, were prepared by casting method and their physical properties were compared in order to approve the use of CNC instead of MMT for its contribution in improving the physical properties of carboxymethyl cellulose-based films. The X-ray diffraction results indicated the formation of an exfoliated nanostructure at all nanoparticle concentrations. The results showed that there was no significant difference (p < 0.5) between the moisture absorption properties of films containing the two types of nanofiller. The films containing nanoclay showed higher mechanical strength compared to those containing CNC. The ultimate tensile strengths of the films containing 10% nanoclay and CNC were higher than the control film (69.72% and 47.05%, respectively).

Due to performance grade (PG) zonation of different parts in Iran and poor properties of 60/70 penetration grade bitumens for pavement applications, suitable polymer modified bitumen was produced. To fulfill this purpose, different PMBs samples were produced using 60/70 penetration grade bitumen and various percentages of VB (20 and 25%), with different percentages of SBS Calprene C501 (4, 4.5, 5 and 5.5%), in a high shear homogenizer in 1 h mixing time at 160°C temperature. To determine the performance grade, aging effect, low temperature performance and rheological properties such as evaluation of rutting and fatigue factors some SHRPs measurements (DSR, RV, RTFOT, PAV and BBR) were conducted. The results showed that the sample with 5.5% SBS with 20 and 25% VB, at high temperatures presented good properties such as: the best performance grade (76°C), the highest resistance and elastic behavior in comparison with the other samples. These samples were subjected to rutting and fatigue tests for both aged bitumen in RTFOT and unaged bitumen. The results indicated that adding SBS to bitumen could not improve the performance at low temperatures, compared to 60/70 grade bitumen, but it did improve the properties of polymer-modified bitumen at similar low temperature (-18°C). So, samples with 4, 4.5 and 5% SBS with 20 and 25% VB, are suitable to be applied in provinces which 60/70 grade bitumens are not suitable. In some provinces such as Khoozestan, with a PG of 76, the compositions with 5.5% SBS with 20 and 25% VB, are found to be suitable.

Nanocomposites based on polyamide 6/polypropylene (PA6/PP 67/33) blend containing 2.5 to 10 phr of nano-CaCO3 and 5 phr of maleated polypropylene (PP-g-MAH) as compatibilizer were prepared by melt compounding followed by injection molding. The mechanical properties, water absorption, as well as shrinkage behavior were characterized and the morphology was studied using scanning electron microscopy. The presence of PP, PP-g-MAH and nano-CaCO3 lowered the amount of water absorption as high as 72 wt%. Morphology analysis indicated that the addition of PP-g-MAH can significantly improve the adhesion between PA6 and PP phases. The incorporation of PP-g-MAH led to 24% increase in flexural and impact strength, 27% rise in tensile strength and approximately 100% increase in elongation-at-break. The addition of nano-CaCO3 particles increased the impact resistance and flexural strength. The results of experiments indicated that the maximum flexural strength was achieved by adding 5 phr of nano-CaCO3 which was 16% greater than pure PA6, and the maximum impact strength was attained by adding 7.5 phr of nano-CaCO3 which was 29% superior compared to pure PA6. The incorporation of 10 phr of nano- CaCO3 particles led to filler agglomeration and, consequently, the impact strength was dramatically dropped. Dimensional characterization of molded samples revealed that the incorporation of PP-g-MAH can raise the shrinkage, but the addition of nano- CaCO3 has not had any considerable effect on the shrinkage of nanocomposites.

The clay crosslinked hydrogel nanocomposites were synthesized by graft copolymerization of acrylamide and itaconic acid in the presence of different amounts of laponite using ammonium persulfate and N,N,N',N'- tetramethylethylene diamine (TEMED) as a free radical initiator and catalyst, respectively. The XRD patterns of nanocomposites showed that the clay layers are completely exfoliated and uniformly dispersed in polymeric matrix. The effect of laponite content on the equilibrium swelling and cationic dye uptake of crystal violet was investigated. It is observed that with increasing clay content in hydrogel composition, the water absorbency is increased. In the dye absorption studies, it was found that amount of dye uptake and removal efficiency increased with increasing laponite content. Also, the synthesized samples adsorb higher amount of crystal violet in higher concentrations of dye. Therefore, these nanocomposites could be used for removal of crystal violet dye from wastewater.