Preparation and Characterization of Cationic Poly Vinyl Alcohol with A
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European Polymer Journal 47 (2011) 997–1004 Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj Preparation and characterization of cationic poly vinyl alcohol with a low degree of substitution ⇑ Pedram Fatehi a, , Robin Singh a,b, Zainab Ziaee a, Huining Xiao a, Yonghao Ni a a Department of Chemical Engineering, Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, NB, Canada E3B 5A3 b Department of Chemical Engineering, Indian Institute of Technology, Kharagpur, India article info abstract Article history: The cationization of polymers has been regarded as an effective method to improve their Received 23 December 2010 performance for various applications. In this work, the cationization of poly vinyl alcohol Received in revised form 16 February 2011 (PVA) was investigated under different conditions, i.e., various glycidyl-trimethylammoni- Accepted 27 February 2011 um chloride (GTMAC) to PVA ratios, reaction temperatures, times, PVA and NaOH concen- Available online 3 March 2011 trations and solvent compositions. The results showed that the overall efficiency of the cationic modification was rather low, which was due to the hydrolysis of both GTMAC Keywords: and cationic-modified PVA (CPVA) under the strong alkaline conditions employed. The Cationization results also showed that the optimum GTMAC/PVA ratio depended on the solvent compo- Poly vinyl alcohol 1 AFM sition. The cationization was confirmed by means of H NMR and FTIR analyses. The max- NMR imum efficiency in water was obtained under the conditions of 95 °C, 1 h, 0.5 (mol) FTIR GTMAC/PVA ratio, and 5% (mol) NaOH concentration, while that in the ethanol/DMSO mix- Polymer ture (1.25 v/v) was obtained under the conditions of 70 °C, 1 h, 0.5 (mol) GTMAC/PVA ratio, and 5% (mol) NaOH concentration. Additionally, the interaction of CPVAs with a silicon wafer (as a substrate) was determined by employing an atomic force microscope (AFM) in water and air. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction cationic PVA (CPVA) [5]. The highest MW of the resulting CPVA was 80,000–90,000. On the other hand, the cation- Cationic polymers have been applied in various indus- ization of already produced polymers on the basis of graft- tries for different purposes. For example, they have been ing is a simpler process since the cationization degree can used as strength agents or retention aids in papermaking be controlled without any effect on the molecular weight [1–4]. Copolymerization and grafting have been regarded of polymers. The modification of poly vinyl alcohol (PVA) as useful methods to induce tailored cationic polymers in using various chemical agents was reported in the litera- the literature [1,5]. ture [6–9]. Although copolymerization is an efficient method to In our previous work, the cationic-modified poly vinyl produce the cationic polymers, simultaneously controlling alcohol (CPVA) showed promising results in improving the molecular weight (MW) and charge density of the the pulp and paper strength [10,12–14], and the best re- resulting cationic polymers may be a challenging task, as sults were obtained at employing PVA with the molecular these properties are interrelated [5]. The copolymerization weight of 142,000–186,000 [11]. Additionally, it was found of vinyl acetate and diallyldimethyl ammonium chloride that the optimum charge density of CPVA for various fiber (DADMAC) was conducted in our previous work to produce systems may be different, varying between 0.3 and 0.72 meq/g, depending on the types of the fiber systems [10,12,13]. Therefore, it is important to understand the ⇑ Corresponding author. Tel.: +1 506 452 6084; fax: +1 506 453 4767. influence of parameters affecting the cationization of PVA E-mail address: [email protected] (P. Fatehi). with a tailored charge density. 0014-3057/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2011.02.021 998 P. Fatehi et al. / European Polymer Journal 47 (2011) 997–1004 In the literature, the cationization of starch and hemi- 2.3. CPVA characterization celluloses were conducted under various conditions, including wet or semi-dried environments [15–18]. The To determine the charge density of CPVAs, their solu- cationization reaction was also conducted in various sol- tions (1% wt.) were titrated against a PVSK standard solu- vents, e.g., water, ethanol or dimethyl sulfoxide (DMSO) tion (0.5 mM) by using a Particle Charge Detector Mütek [19,20]. In the cationization reaction, glycidyl-trimethy- PCD 03 (Herrsching, Germany). To quantify the degree of lammonium chloride (GTMAC) has been commonly used substitution of GTMAC with hydroxyl group on cationic- as a cationic reagent [15–20]. modified PVA (CPVA), CPVAs were dried at 105 °C over- 1 An atomic force microscopy (AFM) has been employed night, and their H NMR spectrum was recorded in D2O as a powerful device to investigate the interactions be- at 25 °C using an Oxford 300 MHz spectrometer operating tween various materials [21–23]. This device can be used at 300.13 MHz [8,9]. to determine how the charge of polymers influences The unmodified PVA and CPVA with the charge density their attraction/repulsion force with soft or hard surfaces. of 1.08 meq/g, which was prepared under the conditions of In this research, we aimed at understanding the factors 11% (wt.) PVA, 0.5 (mol) GTMAC/PVA ratio, 5% (mol) NaOH influencing the cationization of high MW PVA to induce concentration(based on PVA), 90 °C, 1 h, were character- CPVA with a low charge density (<1 meq/g) under vari- ized by using a Fourier transform infrared spectroscopy ous conditions. The parameters evaluated were: (FTIR) (Perkin Elmer Spectrum 100 FT-IR Spectrometer, GTMAC/PVA ratio, temperature, time, PVA concentration, USA). The oven-dried PVA or CPVA were embedded in solvent composition and NaOH concentration. The cati- KBr pellets in a mixture of about 1% (wt.) KBr. The spectra onization of PVA was confirmed qualitatively via FTIR were recorded in a transmittance mode in the range 800– and quantitatively via 1H NMR analyses. Based on these 3800 cmÀ1. results, the conditions that could induce the CPVA with a desired charge density and the maximum cationization 2.4. AFM analysis efficiency were determined. Moreover, the interaction of CPVA (having a low charge density of 0.2 meq/g or a In the literature, the AFM technique was employed to high charge density of 1.3 meq/g) with a silicon wafer determine the interaction between CPVAs and a hard sur- (as a substrate) was determined via employing an AFM face [21–23]. In fact, the silicon wafer with a 100 nm ther- in either water and air. mally oxidized layer was used as a model substrate for cellulose fibers [21–23]. In this work, similar silicon wafers were first immersed in 98% H2SO4 for 6–8 h and rinsed 2. Experimental with deionised and distilled water prior to the use [21– 23]. To investigate the interaction of CPVA with the silicon 2.1. Raw materials wafers, an atomic force microscope (AFM) Nanoscope IIIa, Veeco Instruments Inc., Santa Barbara, CA, was employed. Poly vinyl alcohol (PVA) with a molecular weight (MW) The force analysis was conducted by using silica nitrate of 142,000–186,000 (99% hydrolyzed), glycidyl-trimethy- probes (NP-S20) with a spring constant of 0.32 N/m, and lammonium chloride (GTMAC, 75% in water), potassium a resonance frequency of 273 kHz. This silica probes were bromide (KBr, analytical grade), and dimethyl sulfoxide coated with CPVAs according to the following procedure: (99.7%, sterile-filtered), were all obtained from Sigma– at first, the probes were immersed in CPVA solutions (2% Aldrich, and used as received. Anionic polyvinyl sulfate wt.) overnight; then, the CPVA-coated probes were washed (PVSK) with a MW of 100,000–200,000 (97.7% esterified) with deionised and distilled water to remove unadsorbed was provided by Wako Pure Chem. Ltd. Japan. Ethanol CPVAs from the probes. The adhesion/repulsion force (95%) was received from Fisher Scientific. developed between the CPVA-coated probes and silicon wafers was measured in Picoforce mode with a vendor- supplied fluid cell at the temperature of 25 °C and the pH 2.2. CPVA preparation of 7 in water or in air. Each of 50 different spots was scanned 5 times on an area of 1 Â 1 lm2 at a constant tip In this research, 1 g of PVA was mixed with GTMAC un- velocity of 0.5 lm/s. The force-distance curves were ob- der various conditions. The reaction parameters investi- tained from cantilever deflection and displacement of the gated were: GTMAC/PVA ratio (0.25–2 mol), PVA piezo. concentration (4–33% wt.), solvent type (water, ethanol, ethanol/water or DMSO/ethanol), reaction time (20 min– 240 min) and temperature (60 °C–95 °C) and NaOH con- 3. Results and discussion centration (1–15% mol based on PVA). All the reactions were conducted in a 250 ml 3-neck glass flask under a con- 3.1. Preparation of cationic PVA stant stirring. The cationization reaction was stopped via neutralizing the solution using HCl (1 M). Then, the solu- 3.1.1. Effect of PVA concentration tions were cooled to room temperature, and unreacted Fig. 1 shows the charge density of the CPVA as a func- GTMAC was separated by dialyses membranes having a tion of PVA concentration. As can be seen, by increasing molecular weight cutoff of 1000, while changing water the PVA concentration from 4% to 33% (wt.), the charge every 2 h for the first 6 h and then once a day for 2 days.