Iranian polymer journal
Volume:19 Issue: 4, 2010

Various Comonomers in Acrylonitrile BasedCopolymers: Effects on Thermal BehaviourNa Han*, Xing-Xiang Zhang, and Xue-Chen WangTianjin Municipal Key Lab of Fiber Modification and Functional Fiber,Institute of Functional Fibers, Tianjin Polytechnic University,Tianjin-300160, PR ChinaReceived 24 April 2009; accepted 25 January 2010Identification of suitable comonomers and achieving their optimum molar contentsare the main objectives of this investigation, in which, a series of acrylonitrile (AN)copolymers were synthesized with comonomers (AN/M), such as methyl acrylate(MA), vinyl acetate (VAc) and acrylamide (AM) by aqueous precipitationcopolymerization. The molar feed contents of the comonomers were 5-25 mol%. Thecopolymers were characterized by using Fourier transform infrared spectroscopy,nuclear magnetic resonance (1H NMR), differential scanning calorimetry, thermogravimetry(TG) and X-ray diffraction (XRD) analyses. 1H NMR studies revealed thatthe compositions of AN/MA agreed best with the feed molar ratios. Differential scanningcalorimetry (DSC), thermogravimetry (TG) and X-ray diffraction (XRD) results showedthat the effect on delaying cyclization reactions, depression of melting points andcrystallinities, all ranged in the order MA > VAc > AM for various types of comonomers.With comonomer contents increasing, it was interesting to note that the decompositiontemperature of AN/MA shifts continuously to higher temperatures. With increasedcomonomer content, the decomposition temperature of AN/VAc is initially increasedand then decreased. For AN/AM, it shows an opposite trend to that of AN/VAc.Incorporating 15 mol% of MA, melting peak value (Tm) and crystallinity of the AN/MAdrop to the lowest values of 174°C and 18.5%, respectively. The decomposition peakvalue (Td) of AN/MA with the feed molar ratio of 85/15 increases to 321°C. There is awider window of 147°C for melt processing of AN/MA. It is concluded that MA is themost suitable comonomer for enhancing the melt processing of PAN basedcopolymers.

Ammonium pentaborate (APB) is used as fire retardant in polymers or additive inproducing wood-based composites. In order to understand the reactionsbetween APB and aqueous phenol formaldehyde (PF) resin to provide areasonable explanation of the properties of wood composites made with APB modifiedPF resin, the effect of APB on curing behaviour of aqueous PF resin was investigated,by using dynamic differential scanning calorimetry (DSC) and Fourier transforminfrared spectrometry (FTIR) studies. Activation energies at each conversion point ofPF resin reference and its mixtures were calculated by Kissinger-Akahira-Sunose(KAS) algorithm according to isoconversional kinetic method. The enthalpy change ofreaction, the conversion progress with temperature, and the chemical groups in PFresin formed by APB were analyzed at the same time. The results showed that additionof APB at about 3.20 wt% brought about a minute distinction between addition andcondensation reactions. However, as the loading of APB increased to 8.88 wt%,another exothermal peak was observed at temperature around 172°C. The consistentdata of activation energy and enthalpy suggested that this peak was caused by thesecond curing process in APB modified PF resin systems, which helped the completionof cure reaction but delayed the curing time. This second curing process wasconsidered to include the following features: the formation of more stable methylenebridges, addition reactions between eliminated formaldehyde and active groups on PFresin and the formation of hexamine which were consistent with FTIR resultscharacterized by the altered network.

Polymeric micro-networks architecture (PMNs) based on chitosan and its graftcopolymer with acrylamidoglycolic acid (AGA) by precipitation and cross-linkingmethods for the controlled release of 5-fluorouracil (5-FU) is described. Thechitosan and its graft copolymers are cross-linked with different ratios of ureaformaldehyde(UF) in the presence of acidic alcohol media at room temperature. Thenetworks are characterized by Fourier transform infrared spectroscopy, particle sizeanalysis, scanning electron microscopy, differential scanning calorimetry, andX-ray diffraction studies. The physicochemical characteristics (i.e., encapsulationefficiency, density, particle size distribution, in vitro release) of the PMNs are reported.The extent of cross-linking is studied in terms of size of PMNs as well as their releasecharacteristics. Extent of drug loading on the encapsulation efficiency of themicroparticles is investigated to prove their linear relationship. The in vitro releaseperformed in 1.2 pH solution followed by 7.4 pH buffer media, has been analyzed withan empirical equation to understand the diffusion nature of drug solution through thePMNs. The study of 5-FU loaded PMNs shows that the extended release rates arenoticed from the conventional dosage release duration beyond 18 h.

Samples of phase-change materials (PCM) microcapsules containing solidparaffin or camel fat as core materials were synthesized by in situ polymerizationusing melamine-formaldehyde as shell material. The microcapsuleswere made in two consecutive steps, emulsification of PCMs in water and the,encapsulation. Differential scanning calorimetry (DSC), Fourier transform infra-red(FTIR) spectroscopy, optical and scanning electron microscopy (SEM) and particle sizeanalysis were used to characterize the microcapsules. A simple test method wasdevised to visually examine the oil seepage and leaking from microcapsules. Forparaffin microcapsules the effect of agitation speed, through a limited range, wasexamined on the size of microcapsules during the formation of pre-polymer. Themicrocapsules were prepared from camel fat by the similar procedure used for theparaffin microcapsules. The microcapsules were spherical in shape with harsh surfacesas observed by SEM. The average diameter of camel fat microcapsules with 95%confidence limits is 1515±199 nm and that of paraffin is 1600±341 nm. The shell resinwas strong and stable enough to prevent the liquid oils from seepage and leaching at80°C. The effect of prepared camel fat microcapsules on the delay of heat wasdetermined through examining a covered polyester/viscose-fibre fabric. The loadedfabric samples with 10% (w/w) camel fat microcapsules delayed the rise of temperatureof the covered thermometer when exposed to heat at 50°C oven. Newton''s law of cooling was applied to determine the delay in temperature change.

The aim of this work is to introduce a novel chemical recycling approach forpolyurethane foam wastes which can produce useful chemicals. Flexiblepolyurethane foam was dissolved in a mixture of diethylene glycol (DEG) andpentaerythritol (PE). PER is a useful choice in recycling processes because of its OHfunctional groups and its structural similarity to polyols. Meanwhile, there are severalenvironmental advantages for chemical recycling of polyurethane foam wastes due tothe capabilities of the above method. The trans-esterification process cleaves theurethane structure, producing OH containing chemicals. The product is separated in 2phases which are both useful in the production of new PU foams. The split product wascharacterized by several analytical methods, e.g., chromatography and spectroscopy.Optimum reaction condition and the role of recycled polyol on foam properties wereinvestigated, as well. The solvent system contained DEG/PER as 9/1 ratio. Sodiumhydroxide was used as the catalyst and the optimum reaction time was 4 h. Separatedphases of the product are reusable in polyurethane foam formulation: upper phase inflexible (40%) and lower phase in rigid (30%) foams to obtain desirable physicalproperties in the final product. This method can be introduced as a route for reductionof environmental hazardous materials, while regenerating valuable raw materials.

Blends of linear low-density polyethylene (LLDPE)/poly(vinyl alcohol) (PVA) wereprepared by conventional thermoplastic processing technique. The blends weremixed using a Haake rheometer at 150°C and 50 rpm for 10 min. The LLDPEand PVA were blended to give the following blend ratios (php): 90/10, 80/20, 60/40,50/50 and 40/60. The effect of maleic acid via in situ cross-linking on processability,component interaction, miscibility, thermal stability, tensile properties, and morphologyof LLDPE/PVA blends was investigated in this research. The results indicated that thepresence of maleic acid increases the equilibrium torque of LLDPE/PVA blends. Thisobservation may be due to better compatibility and cross-linking between LLDPE andPVA. The formation of cross-linking was confirmed by Fourier transform infraredanalysis and depression of melting points of PVA and LLDPE in the blends. Thethermal stability and mechanical properties such as tensile strength, elongation-atbreak,and Young''s modulus of the LLDPE/PVA blends also improved in the presenceof maleic acid. Evidence for greater compatibility between LLDPE and PVA wasconfirmed by emergence of elongated fibrils extending over the surface of the PVAdispersed phases in the LLDPE matrix as revealed by scanning electron microscopymicrographs.

By reacting p-tert-butylthiacalix[4]arene with ethyl chloroacetate using KI ascatalyst in K2CO3/acetone, 5,11,17,23-tert-butyl-25,26,27-tri-ethoxy-2-acetylthiacalix[4]arene and 5,11,17,23-tert-butyl-25,26,27,28-tetra-ethoxy-2-acetylthiacalix[4]arene were prepared in moderate yields. Their further reactions withbi-(ethyleneimine) or tri-(ethyleneimine) produced the first examples of four tri-bridgedand tetra-bridged thiacalix[4]amido-based polymers with porous and netty architecturesin yields of 81%, 84%, 86%, 89%, respectively. The structures of these polymers wereconfirmed by FTIR, elemental analysis, 1H NMR, and SEM, etc. The Mn of these novelpolymers were 18000~22000 which indicated that approximately 17~20 thiacalix[4]arene units are present in each polymer molecule. The adsorption experiments of thesenovel polymers showed excellent adsorption abilities for soft metal cations Ag+, Hg2+,Cu2+, Co2+, Ni2+, Cd2+, and Zn2+, but low adsorption towards hard metal cations Na+and K+. Also, these novel polymers exhibited outstanding adsorption capacity for aseries of aniline derivatives. The highest adsorption percentages were 93.4% and94.2% for Cu2+ and p-nitroaniline, respectively. The saturation adsorption capacities ofthiacalix[4]amido-based polymer with tri-(ethyleneimine) for Cu2+ and p-nitroanilinewere as high as 1.51 mmol/g and 1.34 mmol/g, respectively. The adsorptionpercentages of novel polymers reduced sharply in pH < 4, but they can be recycled bydesorption in 10% ammonia solution.