Papers by Keyword: Initiator

Abstract: This research focused on the effect of initiator and accelerator amounts on mechanical properties of unsaturated polyester resin (UPR). Methyl ethyl ketone peroxide (MEKP) and cobalt octoate (CoO) were used as an initiator and an accelerator, respectively. The amount of each chemical was varied from 1, 1.5 to 2 phr. In each batch, UPR, MEKP and CoO were mixed, casted and allowed for curing at room temperature for 24 hours. Mechanical properties of the cured samples were then studied. The results indicated that the effects of MEKP and CoO amounts on flexural properties and impact resistance were greater than those on hardness. It was found that UPR samples prepared by using the same ratio of MEKP and CoO exhibited overall mechanical properties better that those prepared with different MEKP and CoO ratios. When all mechanical properties were considered, the results suggested that the best overall mechanical properties were achieved when MEKP 1.5 phr and CoO 1.5 phr were employed.

Abstract: Photopolymerisation of 2-Hydroxyethyl methacrylate (HEMA) through the use of N,N-Diethyldithiocarbamato-(1,2)-propanediol (DCPD) was studied. The photoinitiator DCPD was synthesized from sodium N,N-Diethyldithiocarbamate (NaSR) and 3-chloro-1,2-propanediol. For the photochemical decomposition of the C – S bond, UV light at 254 nm is used. The role of the monomer concentration, reaction time and DCPD to HEMA mol ratio on the conversion of HEMA to PHEMA were studied in this paper. It was found that percentage conversion of HEMA increased both with the rise in concentration of monomer and reaction time. Further, living radical nature of the poly2-Hydroxyethyl methacrylate (PHEMA) was ascertained by the photo block copolymerization of methyl methacrylate (MMA) with PHEMA to form PHEMA-b-PMMA. The PHEMA and PHEMA-b-PMMA were characterized by FTIR, ¹H-NMR, Thermogravimetry.

Abstract: At present, the products of polycarboxylate superplasticizer (PCE) mainly present liquid state. Compared with liquid PCEs, solid PCEs have not only high storage stability, but also high water-reducing rate. Based on acrylic acid (AA) and isobutenyl polyethylene glycol (IPEG) as the main materials, a series of solid PCEs were synthesized under anhydrous condition by employing ammonium persulfate (APS), benzoyl peroxide (BPO), azobisisobutyronitrile (AIBN) and azobisvaleronitrile (ABVN) as initiators, and the effects of different initiators on the application performances of these solid PCEs were also investigated. The molecular characteristics of the synthesized products were determined by Infrared Spectroscopy (IR) and molecular weight measurements to confirm the expected structure. The fluidities, dispersions and micro-observations of cement pastes containing solid PCEs were evaluated. For both liquid PCE and PCE-ABVN, the average particle size reduced from 2373nm to 1147nm. The results showed that the paste fluidity, concrete slump and retentions were significantly enhanced when using ABVN as initiator, with the initial slump up to 225mm. This initiator had high initiating efficiency, exhibiting broad application prospects.

Abstract: Abst r a c t. Polystyrene (PS) nanospheres were synthesized by emulsion polymerization using 2,2′-Azobis (2-methylpropionitrile) (AIBN) as initiator and Sodium dodecyl sulfate (SDS) act as surfactant. The size and distribution of the PS nanospheres were systematically investigated in terms of surfactant concentration. Effect of the surfactant towards to the particle size is study using SEM, FTIR and XRD. It is found that increase in Sodium dodecyl sulfate (SDS) concentration increase the reaction time thus longer time needed for the formation of the nanosphere. However their properties are comparable to the commercial Polystyrene PS nanosphere.

Abstract: Rice Husk Superabsorbent Polymer Composites (RH-SPC) were synthesized through solution polymerization by using Acrylamide (AM) and Acryl Acid (AA) as monomer, Ammonium Persulphate (APS) as initiator and N, N-methylbisacrylamide (MBA) as cross-linker and rice husk (RH) as filler. The amount of rice husk filler and crosslinking agent were varied before the water absorbency (Q) of the prepared RH-SPC were tested by using tea bag method at different pH solution. In this study, the buffer solutions were prepared by the mixing of Hydrochloric Acid (HCl) and Sodium Hydroxide (NaOH). It was found that RH-SPC with the increment of 10 wt% (44.80 g/g) of rice husk filler and 0 wt% (91.40 g/g) of crosslinker results in the highest water absorbency value. Meanwhile, the best pH condition of 10 wt. % of rice husk husk filler and 0 wt% of crosslinker content show the optimum water absorbency at pH 8 and pH 6 with the value of Q are 51.20 g/g and 280.10 g/g, respectively.

Abstract: ATRP is one of the most active fields in polymer science. The feature of ATRP is chain propagation by way of transfer of halide atom with or without the catalysis of transition mental compounds. The termination reaction between radicals is reduced by low concentration of free radicals under the control of the fast transfer. A variety of monomers including styrene, acrylates, methacrylates, and dienes can be used in this technique. ATRP is a simple and inexpensive process for controlled "living" radical polymerization leading to well-defined homopolymers and copolymers. In this paper, the mechanism, initiator, catalyst systems, polymerization mediums and conditions of ATRP are introduced, the prospect of ATRP is also discussed.

Abstract: Emulsifier-free emulsion polymerization is a technique derived from conventional emulsion polymerization in which polymerization is carried out in the absence of emulsifiers. This technique is useful for the preparation of polymer colloids with narrow particle size distributions and well defined surface properties. Emulsifier-free emulsion polymerization eliminates the disadvantages of conventional emulsion polymerizations stemming from the use of emulsifiers, e.g. impurities in products caused by residual emulsifier and poor water-resistance of films induced by polymer latex.

Abstract: The effect of benzoyl peroxide (BPO) as an initiator in H₂O₂ slurry for abrasive-free chemical polishing of hard disk substrate was investigated. The results of abrasive-free polishing tests show that the introduction of BPO increases material removal rate (MRR) and decreases the value of Roughness (Ra). To further investigate the mechanism of abrasive-free polishing, electron spin-resonance spectroscopy (EPR) tests, auger electron spectrometer (AES) and electrochemical tests were conducted. Electron spin-resonance spectroscopy (EPR) tests show the concentration of radicals increase and promote the reaction on the surface of hard disk substrate. Auger electron spectrometer (AES) and electrochemical tests indicate chemical changes happen on the surface of hard disk substrate, and the formed oxide film may be sparse or porous. The results imply that the introduction of BPO can effectively improve the effect of abrasive-free polishing.

Abstract: initiator is one of the most important conditions of synthesizing efficient strength agent CPAM. To begin with initiating mechanism, three redox systems of acrylamide aqueous polymerization (NH₄)₂S₂O₈/ Na₂ SO₃, K₂S₂O₈/NaHSO₃ and K₂S₂O₈/Na₂ S₂O₄ have been studied. The effects of different kinds of initiator, initiator concentration, and monomer concentration as well as polymerization temperature on relative molecular weight and strength effects of CPAM have been investigated. K₂S₂O₈/Na₂ SO₃ is the most useful system in synthesizing efficient strength agents.

Abstract: According to the radio frequency effect mechanism, the performances of SMD capacitor used for RF protection of SCB initiators were studied theoretically and experimentally. The 99.9% firing RF power of SCB initiators without any protection is 14.15W, but none of SCB initiators in parallel with SMD capacitor fired at 20W. The results of capacitor discharge experiment indicate that SMD capacitor has no influences on electrical explosive performances of SCB initiators. Its RF protection capability for SCB initiators of SMD capacitor was tested by RF sensitivity experiment, and the results show that it could significantly reduce the RF sensitivity of SCB initiators when in parallel with appropriate SMD capacitor.