Preparation and Characterization of Water-Soluble Acrylic Pressure Sensitive Adhesive

Open Access Journal of Waste Management & Xenobiotics ISSN: 2640-2718

Preparation and Characterization of Water-soluble Acrylic Pressure Sensitive Adhesive

Juhyeon L1 and Jaehee L2* Research Article 1Hankuk Academy of Foreign Studies, Korea Volume 1 Issue 2 Received Date: November 01, 2018 2Gaia Corporation, Korea Published Date: November 15, 2018

*Corresponding author: Jaehee Lee, Hankuk Academy of Foreign Studies, 32-36 DOI: 10.23880/oajwx-16000110 Yuseongdaero, 1596beon-gil, Yuseong-gu, Daejeon, 34054, Korea, Tel: +82 423849706; Email: [email protected]

Abstract

In order to evaluate the adhesion performance, tack, peel strength, shear strength, and water solubility of pressure- sensitive adhesive (PSA), we prepared PSA copolymers using 2-ethyl hexyl acrylate (2-EHA), butyl acrylate (BA) and acrylic acid (AA) with varying AA contents through solution polymerization in methanol. After preparing the PSAs, we neutralized the AA in the PSAs with potassium hydroxide (KOH). Polypropylene glycol (PPG) was blended with the PSAs as a surfactant before testing adhesion performance and water solubility. Tack was characterized by probe tack testing, shear strength was evaluated with these hear adhesion failure temperature (SAFT) method, and peel strength was measured by 180° peel testing. The water solubility test was performed by comparing weight of before immersing the PSA blends in distilled water and after removing the PSAs blends from water. Water solubility was increased along within creased AA and PPG contents in the PSA blends.

Keywords: Water-Soluble; Pressure sensitive Adhesive; PSA; Acrylic

Abbreviations: PSA: Pressure-Sensitive Adhesive; 2- problems in paper-making such a sit becoming stuck to EHA: 2-Ethylhexyl Acrylate; SAFT: Shear Adhesion Failure the felts, wires, and dryer cylinders of paper machines, Temperature; TAPPI: Technical Association of Pulp and thus causing web breaks, reducing production, and Paper Industry (TAPPI). lowering the quality of the recycled paper [4]. Among them, PSAs are the main obstacles in repulping and Introduction paper-making.

As the need for environmental protection increases, so The utilization rate of recycled paper rose from 31% has the interest in the protection of forests, and many in 1991 to 39% in 1996 in the U.S.A., from 50% to 60% in studies have been conducted on the repulping and Germany, from 60% to 70% in the U.K., from 46% to 49% recycling of waste paper in the paper industry [1-6]. in France, and from 32% to 35% in China. However, the However the recycled fiber has many contaminants such annual cost of stickies to the U.S. paper industry is as stickies, low Tg derived from ink, coating material, estimated to be about $600,000,000 –$650,000,000 [4]. pressure-sensitive adhesive (PSA), etc., which create Therefore, much research has been completed focusing on

Preparation and Characterization of Water-soluble Acrylic Pressure Sensitive Adhesive J Waste Manage Xenobio 2 Open Access Journal of Waste Management & Xenobiotics

sticky control and development of new PSAs. Although Analysis of PSAs stickies can be reduced by treating paper-making The glass transition temperature (Tg) was measured machines and adding dispersion agents, when the pH, using a differential scanning calorimeter (DSC, TA temperature, concentration, charge, and shear force Instrument Co. Q-1000) from -80°C to 200°C at a rate of conditions change, stickies can accumulate on paper 10°C/min. The molecular weight was measured using gel machine felt, wire, dryers, and other places [1-3,5-6]. So permeation chromatography (GPC, Waters 486). new PSAs for the repulping process must be developed

[1-3]. Adhesion Performance of PSA blends In this study, water soluble PSAs were polymerized PSA performance was evaluated by probe tack, peel through solution polymerization using 2-ethylhexyl strength and SAFT testing. The probe tack and peel acrylate (2-EHA), butyl acrylate (BA), and acrylic acid (AA) strength tests were conducted using a Texture Analyzer with varying AA contents. Synthesized PSAs were (Stable Micro Systems, TA-XT2i). The probe tack test was neutralized with potassium hydroxide (KOH) and blended carried out with a polished stainless steel cylinder probe with polypropylene glycol (PPG). Adhesion performance 5mm in diameter, a separation rate of 0.5 mm/sec. under 2 of the prepared PSAs was evaluated by probe tack, peel a constant pressure of 100 gf/cm and a dwell time of 1 strength, and shear adhesion failure temperature (SAFT) second. The peel strength test was performed at an angle testing. The water solubility of each PSA was also tested. of 180° with a cross-head speed of 300 mm/min after keeping the sample at room temperature for 1 hr. For Materials and Methods SAFT, the PSA samples were pressed onto SUS (Stainless steel) (Bonding area of 25 mm × 25 mm) with two passes Materials of a 2 kg rubber-roller. A load of 1 kg was attached to one end of the lap shear, while the bonded area was adhered 2-EHA, BA, and AA used to prepare acrylic PSAs were to the stainless steel substrate. The failure temperature obtained from Junsei Chemicals Co. and used as received. was measured as the temperature was increased at 2,2-Azobisisobutyronitrile (AIBN), methanol (Duksan 0.4°C/min. pure chemical Co.), KOH (Deajung Chemicals Co.), and

PPG (PPG, Mn~1000, sigma-aldrich) were used without further purification. Water solubility of PSA Blends 5 g of dried of PSA was added to 200 mL of distilled Preparation of PSAs water and the mixture was agitated at 50°C for an hour. The weight ratio was calculated using the following The acrylic PSAs were prepared through solution equation after measuring the weight of the adhesive polymerization as 50% solids in methanol. Methanol was remaining on the filter after filtering through a 300 mesh added to a 500-ml reaction tank and stirred at 65°C at 200 filter made of SUS. rpm. Then, monomer mixture having the same

composition as Table 1 was added and stirred at 65°C for W 7 hours. The polymerized PSA was transferred to a PE Water-solubility (%)  a 100 container and left at room temperature for 48 hours to Wb confirm the stability of the polymer. KOH was dissolved in Wa : weight of PSA after filtered water and methanol at a weight ratio of 200: 100: 100 to Wb : weight of PSA before filtered prepare a 50% solution. The molar ratio of each AA of the polymerized PSA was neutralized with KOH solution. Repulpability of PSA Blends Then, PPG was blended with 10 wt%, 20 wt%, 30 wt%, 40 wt%, and 50 wt% of the solid content of the neutralized The coated PSA was transferred to copy paper. The PSAs. paper was torn into small pieces and soaked in distilled water with a 10% consistency for 1 hr. The mixture was 2-EHA (wt%) BA (wt%) AA (wt%) disintegrated in a standard disintegrator with the propeller operating at 3000 rpm. A hand sheet was made A-5 20 75 5 according to Technical Association of Pulp and Paper A-10 20 70 10 Industry (TAPPI) standard method T 261. The sticky A-15 20 65 15 particles on the hand sheet were identified by unaided A-20 20 60 20 visual means.

Table 1: PSA Co-Polymer Formulations.

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Results and Discussion and A-15, the tack value was increased and maintained. However, with the addition of 40 wt% or more, Table 2 shows the Tg and molecular weight of the fibrillation occurred during probe debonding and tack polymerized PSAs. As the theoretical Tg of the AA was decreased. This is because the internal cohesion exceeded 100℃, the Tg of the polymerized PSA tended to increased by the KOH is gradually relaxed by the addition increase as the content of AA increased. The acrylic PSA is of PPG and exceeds the critical point of the PPG content, a random copolymer having -30℃ ~ -40℃ of Tg [7-9]. causing fibrillation. This cohesive failure phenomenon When the content of AA in the PSAs increases, Tg also occurred with 40% or more PPG when peel strength increases and physical cross linking occurs due to was measured. When the content of PPG was 0 wt% the hydrogen bonding by the carboxyl group so that the peel strength was not measured for all samples, but the cohesive force is increased. As a result, the tack is lowered peel strength increased as the content of PPG increased. due to the decrease in intermolecular fluidity and the As the amount of PPG added increased, the peel strength adhesion to the substrate is subsequently lowered as well and tack values of A-5, A-10, and A-15 increased and then [9]. decreased, but A-20 showed a different tendency. A-20 exhibited low peel strength from 0 ~ 30wt% PPG and 4 showed cohesive failure at 40wt%.This caused molecular Experimented Tg (℃) Mw× 10 entanglement due to side-chain growth induced by the A-5 -40.9 36 chain-transfer phenomenon during polymerization, and A-10 -32.6 47 due to ionic bonding by KOH. As a result, the molecular A-15 -24.3 40 fluidity was lowered, resulting in lowered peel strength A-20 -8.5 35 and tack. SAFT results showed that SAFT increased when increasing the AA content, but SAFT decreased when Table 2: Tg and Molecular Weight of PSA Copolymers with increasing the amount of PPG in A-5, A-10, and A-15.This Varied AA Contents. is because the PSA ion-bonded by the KOH exhibits heat

resistance when the amount of the PPG added is low The increased AA affected the molecular weight. The because of the lack of fluidity, but since the ionic bond is a molecular weights of A-5 and A-10 were increased, physical crosslink, the added PPG acts as a plasticizer and whereas the molecular weights of A-15 and A-20 were the SAFT decreases as the PPG content increases [8]. decreased. This is because AA has a shorter side-chain However, A-20 showed a SAFT of 200°C until PPG content than other monomers and thus has a high reactivity in of 30wt%, and then it decreased. It seems that the side polymerization. Therefore, when the content of AA chains generated during the polymerization process increases during the polymerization, the reactivity of the contributed to heat resistance in the same way as the AA increases and, thus, the molecular weight is affected. result of the peel strength and tack tests. However, the viscosity of A-15 and A-20 was so high that

additional solvent had to be added when coating them.

This is because the methanol used as the solvent in the polymerization causes the chain transfer phenomenon, the growth of the polymer is stopped, aside chain is formed due to the new radical growth reaction, and intermolecular entanglement occurs [10].

The adhesion properties of PPG-blended PSAs are shown in Figures 1-3. Probe tacking shows the maximum value when the probe sticks to the adhesive specimen for a short time. When the content of PPG is 0 wt%, no tack appears, but tack appears when the PPG content increases. This phenomenon is due to the lowered fluidity of the molecule reducing the tack of the ionic bond with the carboxyl group induced by KOH and high contents of AA in the PSA [8-9,11]. When the content of PPG was increased, acting as a plasticizer and decreasing the cohesive strength of the PSA blends, tack appeared. In Figure 1: Probe Tack Results of PSA Copolymer Blends. addition, as the content of PPG increased to 30 wt%, A-10

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water, the volume of the polymer becomes larger and the polymers, which are entangled with each other, are dissolved in the water. When the PPG content is high, the molecular chain spacing is further increased to increase the solubility of the PSA, and when the AA content is high, the solubility in water is increased due to the large amount of salt produced. Solubility of PSA blends in water was also found in the repulping test. T he part marked in Figure 5 is one in which adhesive that does not dissolve in water forms adhesive residue while bundling with each other. Comparing the solubility and repulping test results, no PSA blend residue was left when the solubility of the adhesive blend in water was greater than 80%.

Figure 2: Peel Strength Results of PSA Copolymer Blends.

120

100

40 A-5 A-10 20 A-15

Water-solubility(%) A-20 Figure 4: Water Solubility Results of PSA Copolymer 0 Blends.

0 10 20 30 40 50 60 PPG contnets (wt%) Figure 3: SAFT Results of PSA Copolymer Blends.

Since methanol was used as a solvent in the polymerization, the AA content affects the stability of the PSAs. When the AA content is less than 4 wt%, when the molecular weight increases during the polymerization, phase separation occurs between the methanol and the polymer. So an AA content of 5 wt% or more was used in this study. The AA content also affects the solubility in water, which is shown in Figure 4. Before the addition of PPG, none of the PSA blends showed any solubility in water, but their solubility increased with increasing PPG content. The solubility in water increased with increasing contents of AA and PPG in the PSA blends. The phenomenon of dissolving in such water is shown in scheme 1. The carboxyl group of the PSA forms an ionic Figure 5: Repulpability Results of PSA Copolymer salt by K+, and the PPG surrounds the pressure-sensitive Blends. adhesive as a surfactant. When it comes into contact with

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adhesives. II. Adhesives from emulsion Scheme 1: Schematic Illustration of Dissolving Process polymerization. J Appl Polym Sci 91(1): 347-353. of PSA Copolymer Blend in Water. 7. Sim MK, Seul SD (2009) Manufacture and properties of water soluble acrylic type PSA′s-effect of functional Conclusion monomer change and atmospheric plasma treatment. Polymer (Korea) 33(1): 45-51. While changing the content of AA, the PSA was solution polymerized with methanol and reacted with 8. Choi HS, Hwang HY, Jeoung SK, Lee SG, Lee KY (2012) KOH. Then the adhesion properties and solubility Adhesive property changes associated with the characteristics in water were examined while changing content of acrylic acid monomer and aziridine cross the content of PPG. When the content of AA in the PSA linking agent. Polymer (Korea) 36(1): 29-33. was 15 wt% and the content of PPG was 30 wt%, it showed higher peel strength, tack, and solubility in water 9. Park MC, Seo IS, Lee MC, Shin HS, Lim JC (1999) than other samples, and no PSA residue was found in the Adheisve property changes of water-based pressure- repulping test. sensitive acryl adhesive with acrylic acid contents and molecular weight. Polymer (Korea) 23(5): 625- References 631.

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