1 / 19

Polyvinyl Acetate Adhesives Forestry 485 Lecture 3-4

Polyvinyl Acetate Adhesives Forestry 485 Lecture 3-4. Background. Vinyl group a.k.a. Ethylene. Self Addition Polymerization. Polyvinyl / Polyethylene. Background. Substituted Ethylene – replacing one H with an Acetate group New Monomer Resulting Molecule.

mcantu
Download Presentation

Polyvinyl Acetate Adhesives Forestry 485 Lecture 3-4

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Polyvinyl Acetate Adhesives Forestry 485 Lecture 3-4

  2. Background Vinyl group a.k.a. Ethylene Self Addition Polymerization Polyvinyl / Polyethylene

  3. Background Substituted Ethylene – replacing one H with an Acetate group New Monomer Resulting Molecule

  4. Background =

  5. Polyvinyl Acetate (PVAc) Properties: Polarity – PVAc is a more polar molecule than polyethylene Polymerization – performed in water, product forms globules that are suspended Bonding – Suspensions are stabilized Little H2O loss results in coalescence and bonding Bond formation in as little as 10 minutes Full strength in 24 hrs

  6. Creep Polyvinyl Acetate (PVAc) • Performance: • Thermoplastic in nature • High temp. softens adhesive • Moisture compromises performance • Under shear PVAc bonds as strong as maple • Perpendicular grain joints are allowed to “flex”

  7. Polyvinyl Acetate (PVAc) • Performance: • PVAc doesn’t fill gaps in an assembly well • Gaps can actually form – Island formation Emulsion is destroyed by freezing temps. • - Tell tale chalky appearance • (as opposed to translucent • appearance of normal cure) • - Application to “cold” surfaces • (< 60 oF) can also adversely • affect emulsion and cure

  8. Polyvinyl Acetate (PVAc) Modification: Aliphatics a.k.a. Carpenter’s Glue Aliphatics – Holdover term from “old days” of chemistry • Properties: • Faster Setting • Can tolerate lower temperatures • More resistant to creep • Less sensitive to moisture and heat • More thixotropic – Less squeeze out

  9. Monitoring the Gluing Operation Brief Overview See: Mara Chapter 10 “Quality Control” (Note: you don’t have this, but a copy will be provided upon request) Glue Prep Application Assembly Time Conditions Pressure Monitoring

  10. Glue Preparation Mixing: Manufacturer’s instructions Pre-Weigh / Pre-Measure Order of addition Mixing Temperature

  11. Glue Application Two Criteria: Ratio of surface area to weight of wood element Low = weight of adhesive per area of glue line Lbs. (liquid) / 1000 ft2 (US) High = weight of adhesive per weight of wood Lbs. (solids) / lbs wood (OD) Application QC – simple measurement One square foot, applied on both sides mass in grams X 1.1 = Lbs. / 1000 ft2 Alternate method – film thickness measurement

  12. Assembly Time Time Sensitivity: Glue may need time to “set up” Too much time - glue dries out Many factors involved in optimum time First layers and last layers most critical (as in plywood lay-up)

  13. Ambient Temperature / Relative Humidity Impact on Time Sensitivity: High temp and/or low humidity - decrease in optimum assembly time Measurement Wet and dry bulb thermometer Sling psychrometer

  14. Pressure Six Basic Mechanisms of Application: • Live Roll • Dead Weight • Spring • Screw • Ram • Pneumatic (Fluid) Pressure

  15. Pressure Terms to Clarify: Load = mass or force imposed on a system (lbs.) Pressure = mass or force imposed on a system over the area of the system (lbs/in2) Example – 200 lb. rock on a 1 ft2 panel Load = ? Pressure = ? Rigid versus Fluid Pressure – Rock versus Sandbag

  16. Pressure Dead Weight Systems – Direct reading systems Pressure = load divided by area Examples: A. 200 lb rock on 1 ft2 panel B. 55 gallon drum of water on same panel C. Same drum hung from lever with 4:1 advantage • 1.39 lb/in2 • 3.17 lb/in2 Load = 55x8.3 = 456.5 lbs • 12.68 lb/in2 Load = 456.5x4 = 1826 lbs

  17. Pressure Spring – Loaded Systems Maintain constant pressure over time “Follow up” Load depends on spring constant and amount of deflection Toggle or spring clamps used in shop- scale work

  18. Pressure Screw Presses Load a function of … Pitch, diameter, torque applied, friction Calibration: torque wrench and load cell Hand Screw Devices: C-Clamp, wood clamps, bar clamps No “follow up” ability inherent

  19. Pressure Hydraulic Presses: Liquid pressure transferred through a piston or ram Ram area x PSI on Ram = Assembly area x PSI on Assembly

More Related