Behavior of Adhesives During Behavior of Adhesives During Paper - PowerPoint PPT Presentation

Behavior of Adhesives During Behavior of Adhesives During Paper Recycling Paper Recycling Steve Severtson, Jihui Guo, Haiyan Li, Helen Xu, Matt Dubay and Mark Calhoun University of Minnesota Carl Houtman USDA Forest Service, Forest Products Laboratory

PSA Market Share and Composition PSA Market Share and Composition for Label Products for Label Products Other Reactive 2% 10% Solvent Based 9% Water Based 59% Hot Melt 20% Defoamer Wetting Agent Rheology Modifier Antioxidant Emulsifier Plasticizer Tackifer Polymer Water Based PSA Hot Melt PSA Polymer Tackifier

Project Objective Project Objective Development of new pressure sensitive adhesive (PSA) products that are Development of new pressure sensitive adhesive (PSA) products th at are engineered for enhanced PSA removal during the screening of recycled fiber engineered for enhanced PSA removal during the screening of recy cled fiber identification of properties that govern PSA removal and development of techniques for formulating benign PSAs characterization of PSA- substrate adhesion and development of techniques for manipulating adhesion to enhance removal development of wet-end recipes for facestock that promotes PSA removal The impact on paper recycling operations should be a design parameter in the development of all PSA systems formulated for label applications

Testing the Removal Efficiency of PSAs Testing the Removal Efficiency of PSAs PSA film is pressed onto facestock Adirondack Formax Temperature Control Pulpers Paper Shredder • consistency = 10% laminates are attached to • 60 Hz ( ≈ 690 rpm) sheets in a sample of copy • typical time = 30 min. paper PSA content = 0.5% 1/4 ″ strips . . . . . . . . . . . . removal efficiency is quantified Rejects Accepts gravimetrically . . . . Valley Flat Screen . . . . . . . TAPPI Method . . 15-cut screen . Cellulose Dissolution T-205 om-88 . . (0.38 mm slots) . & Resin Oxidation . . . . (when required) . Removal IA Area ∝ Efficiency Fraction

Research Strategy Research Strategy Input Input Commercial Assessment Access to Existing of New Product Synthesis and Formulation Product Lines Approaches of Model and Commercial Systems Database Laboratory and Pilot Identification of Key Generation Testing of Screening Characteristics for & Removal Efficiencies Benign Materials Analysis Characterization of Bulk Output Mechanical and Surface Commercially Feasible Properties Benign Products

Hot- -melt melt PSA PSA’ ’s s Hot 20-50 wt. % Base Polymer 30-60 wt. % Tackifier 0-25 wt. % Plasticizer Easily Shaped for Melt Characterization Processing G ′ , G ″ , Tan δ

Predicting Hot- -melt PSA Recycling Performance melt PSA Recycling Performance Predicting Hot 18 Commercial PSA 1 16 SAFT = 57 °C 14 Δ T = 59 °C 12 100 10 8 80 Removal Efficiency (%) 6 Commercial PSA 2 4 T 50 = 80 °C SAFT α = 7.3 °C 2 60 Commercial PSA 1 Tan δ Δ T 0 T 50 = 57 °C α = 6.2 °C 3.5 40 Commercial PSA 2 3 SAFT = 80 °C Δ T = 70 °C 2.5 20 2 Predicted Removal 1.5 0 1 0 20 40 60 80 100 120 SAFT Temperature (°C) 0.5 Δ T 0 -40 -20 0 20 40 60 80 100 120 140 Temperature (°C)

Water- -based based PSA PSA’ ’s s Water Monomers Emulsifier(s) Initiator(s) Crosslinking Agents Polymerization Buffer(s) Biocide(s) Adhesive Emulsion Rheology Tackifying Modifiers Dispersion(s) Wetting Agent(s) Defoamer(s) Formulation Characterization samples restricted to thin films with properties dependent on formulation Formulated PSA Processing requires coating of low energy G ′ , G ″ , Tan δ ? substrate and drying

PSA Latex PSA Latex Colloidal Dispersion of Spherical Polymer Particles in Water 1 μ m anionic and/or carboxylate anions nonionic surfactants on latex surface + + + - + + - - + - + - - COO - + o - -SO 4 o o + - o o o o o positive counterions o - - o o o - COO- + o o o o + o - (Na + , K + , or NH 4 + ) + o o o o - - o o -SO 4 o o o + - o o o COO- o - o o o o o -+- - - - + o + - + - persulfate residues - + coiled, HMW + from initiator polymer chains

Estim ated com positions of w ater- -based PSA latex based PSA latex Estim ated com positions of w ater and film and film Components Coating ready emulsion Dried PSA film(Mass%) dispersion (Mass%) Water 33.06-48.45 0 Monomers 50.21-61.46 88.93-97.79 Emulsifier(s) 1.21-6.58 2.13-9.86 Initiator(s) 0.08-0.31 0.12-0.55 Buffer 0.08-0.59 0.32-1.03 Biocide(s) 0.04-0.25 0.065-0.54 Reducer & oxidizer 0.08-0.93 0.05-0.68 Note: The components of PSA latex film listed above refer to those in adhesive emulsion. Formulated PSAs also contain coating package comprised of tackifying dispersion(s), rheology modifier(s), wetting agent(s) and defoamer(s).

Fate of Latex Additives Fate of Latex Additives Release Liner Release Liner Release Liner TRANSFER COATING “cold flow” in addition to additive migration Facestock Facestock Temperature/Relative Humidity Release Liner Release Liner HIGH Time LOW

Removal Efficiency NOT Controlled by Removal Efficiency NOT Controlled by Performance Properties Performance Properties 25 100 100 20 90 18 90 80 20 80 16 Removal Efficiency (%) Peel Strength (N/25mm) Removal Efficiency (%) Loop Tack (N/25mm) 70 70 14 15 60 60 12 50 10 50 10 40 8 40 30 30 6 20 5 20 4 10 10 2 0 0 0 0 100 40 100 40 90 90 35 35 Surface Energy (mJ/m 2 ) Removal Efficiency (%) 80 Removal Efficiency (%) 80 30 30 70 70 25 25 Shear (hr.) 60 60 50 20 50 20 40 40 15 15 30 30 10 10 20 20 5 5 10 10 0 0 0 0 Commercial Water-based PSA Commercial Water-based PSA

Composition of Model Systems Composition of Model Systems Functional RE Soft Monomer Hard Monomer Model Monomer (%) System MMA VA Styrene AA n-BA EHA MAA M1 2 70.8 10.0 16.0 3.2 M2 57 70.8 10.0 16.0 3.2 M3 79 70.8 10.0 16.0 3.2 M4 10 70.8 10.0 3.2 16.0 M5 77 70.8 10.0 16.0 3.2 M6 70 70.8 10.0 16.0 3.2 M7 75 70.8 10.0 16.0 3.2 M8 90 80.8 16.0 3.2 M9 84 80.8 8.0 8.0 M10 90 80.8 16.0 3.2 M11 81 80.8 16.0 3.2

Tensile Strength vs. Removal Tensile Strength vs. Removal Dry Tensile Force at 22°C Wet Tensile Force at 22 and 50°C 1.4 100 0.45 100 50°C 90 90 0.4 22°C 1.2 Maximum Tensile Force (N) 80 80 Maximum Tensile Force (N) Removal Efficiency (%) 0.35 Removal Efficiency (%) 1 70 70 0.3 60 60 0.8 0.25 50 50 0.2 0.6 40 40 0.15 30 30 0.4 0.1 20 20 0.2 0.05 10 10 0 0 0 0 M 1 M 4 M 2 M 6 M 7 M 5 M 3 M 9 M 8 M1 M4 M 2 M 6 M 7 M 5 M 3 M 9 M 8 Model Water-based PSA Model Water-based PSA Jihui Guo, Steven J. Severtson and Larry G. Gwin INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH 49(9), 2753-2759, 2007

Microstructure Characterization of Microstructure Characterization of PSA film PSA film AFM image Cryo SEM image

AFM of Adhesive Films AFM of Adhesive Films Tapping Mode Contact Mode Cantilever Tip Sample Piezoelectric ( z ) Stage ( x , y ) z y x

Surface morphologies of water- -based based Surface morphologies of water PSA films PSA films Particle size distribution AFM image of PSA film

Surfactant Removal Surfactant Removal Top surface of PSA latex Solvent Soaking for 1 Solvent soaking for 5 film minute minutes

Effect of Moisture Cycles Effect of Moisture Cycles Increase moisture to Initial cycle 3% RH End cycle 3% RH 90% RH

Results Results • Water uptake of PSA films likely controls behavior during paper recycling • Surfactants used to synthesize the original polymers can migrate during processing • Physical properties of wet films can be used to predict removal efficiency during screening

Recycling- -compatible Adhesives compatible Adhesives Recycling (RCA) (RCA) • A committee associated with the Tag and Label Manufacturers Institute (TLMI) have developed test methods and specification for certifying an adhesive is RCA • Several label suppliers are now marketing labels with RCA’s • State of Wisconsin is using this specification for Governmental purchases

Recycling- -compatible Adhesive Testing compatible Adhesive Testing Recycling Adirondack Pulper PSA label is Temperature = 46º C pressed onto envelope paper Consistency = 15% Paper Shredder 40 Hz ( ≈ 500 rpm) at 5% label stock by weight Time = 8 min. 1/4 ″ strips Handsheets Accepts Rejects Accepts Valley Flat Screen 6-cut screen (0.15 mm slots) Handsheets Denver Handsheets Flotation Cell Full description found at http://www.tlmi.com/recycling-standards.php

Summary Summary • Removal efficiency of hot-melt PSAs can be predicted from its dynamic mechanical and performance properties. • Water-based PSAs involve more complex formulations and processing. Removal efficiency is determined by its strength when saturated with water. • The removal efficiency of a PSA is strongly influenced by the overall laminate design and its processing, e. g., the wet-strength of facestock properties can vary the removal efficiency of an attached PSA film by as much as 60%. • Test methods have been developed to certify Recycling-compatible adhesives, and RCAs are now commercially available.