Materials - Foams and Adhesives Lecture

Adhesive Bonds

1. Mechanical Bond - adhesive flows into all the imperfections and scratches, etc. on the surface and when dry form a mechanical bond with the surface. Common bonding method for rubber based cements or adhesives

2. Chemical Bond - adhesive reacts with and forms a chemical bond with the surface it is bonding to. Epoxies are a typical adhesive that forms a chemical bond with the surface they are adhering to

Rubber Based Adhesives

• adhere with a mechanical bond

• adhesive is flexible when set

• best method to bond to Polyolefins (PE, PP, etc.)

• widely used in the shoe industry

Barge Cement

• consists of rubber dissolved in organic solvents

• contact cement - cement is applied to both surfaces and allowed to dry before joining

• adheres to almost any clean surface, bonding wood, rubber, glass, plastic (including polyolefins), leather, cork, metal, plaster, paper, and concrete

• flexible when dry

Poly Adhesive

• uses are similar to barge adhesive

• adheres foams together

• dries clear (not yellow as with barge)

• flexible, strong adhesive well suited to bonding to polyolefins an other plastics

Rubber Cement

• for temporary adhesion

• used like poly-adhesive and barge

• useful for bonding leather to foam, metal, etc.

• used to temporarily bond paper patterns to leather etc. for cutting accurate shapes

Acrylic Adhesives

Orthocryl Sealing Resin:

• for sealing, adhering, and reinforcing

• high-strength adhesive bonds, ex. wood, foam

• combined with filler material for making adhesive putties

• used to ‘gunk’ sockets to wooden block to attach alignment units

Otto Bock SuperGlue

Benefits at a Glance

• 2 component adhesive based on methyl methacrylate with very high adhesive strength

• glueing of metals, duroplastics and htermoplastics without primer

• fast gluing of socket adapters

• processing time - 4-7 minutes

• curing time - 15 minutes

• gel/highly viscous

• fills gaps from 0.5 to 12 mm

• high tensile strength along with excellent peel strength

• high temperature resistance

• lasting strength and flexibility

Polyurethane Quick Set Adhesives

FabTech Systems PLU Series

• tan color

• high strength

• structural adhesive

• resistant to elevated temperatures, moisture, most solvents and chemicals

• 60 second work time

Evolution Industries’ EVO-Bond

• fast curing 2 component urethane

• good balance between strength and resilience

• intended for use in bonding plates to check sockets or inner PETG for definitive sockets

• notable features include:

  • 100% solids urethan chemistry, black pigment for definitive laminations, durability with flexibility, gap filling capabilities, fast cure time

Other Adhesives

1. Epoxy - very strong bonds, adheres to many different materials. 2 component adhesive. Adhesive can be tailored for application

2. Loctite - anaerobic sealing agent - thread locking agent. cures in the absence of air

3. RTV Silicone Sealant/Adhesive - very flexible, durable and heat and weather resistant. But lower tensile strength, tear strength, lower cohesive strength. Good sealant.

Plastic or Polymer Foams

Properties to Consider -

• durometer and density

• compressibility

• shock absorption

• stiffness

• tear strength

• friction

• abrasion resistance

• water absorption characteristics

• durability

• thermoformability

• ease of standing, shaping

• ability to glue

Two Types of Foam

Closed Cell -

• used because they won’t absorb sweat, blood, etc.

• cells are not broken or jointed together

Open Cell -

• spongy and absorb moisture

• cells are connected

Polyurethane Foams

• variety of formulations, properties possible

• flexible to rigid

• open or closed cell

Prosthetic Uses

• Rigid foams - to shape prothesis for exoskeletal designs easy to shape or grind

• Flexible foams - premade covers for TT or TF prostheses and be sanded to shape and covered

PPT (Poron)

• Polyurethane foam

• good shock absorption

• good compression set

• good for insoles

• washable

• open cell design

• NOT good for shear - you can tear it

T - Foam

• Polyurethane based viscoelastic foam

• sensitive areas of the spine

• distributes weight evenly

• temperature sensitive

• expensive

PE Foams

• good heat formability

• very little skin problems

• can heat bond well to plastics (EVA)

• can be soft to firm

• compression set

• hot - no wicking properties

Plastazote

• closed - cell polyethylene foam

• together with PPT for inserts help reduce plantar surface pressure

• lightweight

• will pack down (compression set)

• Crow boot liner, DM inserts

Aliplast (Volara)

• closed cell polyethylene

• smooth surface

• numbering system, ex. 4E - 4 related to its density and E related to the fact that it is an EVA and will bond to copolymer

• XPE or (10) - prosthetic pads and orthosis build-ups

• self sticking when heated

• available with psa on one side

• thermoformable

• easy to grind and shape

Aliplast 4E - Typical Orthotic Uses

• line spinal orthoses

• line lower limb orthoses

• line upper extremity orthoses

• padding in CROs

• site specific pads to relieve areas of high pressure

PE-lite

• expanded cross-linked closed cell polyethylene foam

• light-weight and moisture proof

• dull surface due to cutting from large blocks and smaller cell size

• perforated, ventilated, firm, medium, soft

• good for liners

• can easily thermoform

• doesn’t pack down

EVA (ethylene vinyl acetate)

• closed cell

• light weight, flexible, shock absorbent

• tend to compress over time

• softer and more resilient than PE foams

• used for

  • FOs (top and shell)

  • wedges

  • cushioning/padding material

• available in variety of colors, thicknesses, durometers

  • Evazote

  • Microcel Puff

  • ThermoSKY

P-Cell

• closed cell EVA foam

• similar properties to Aliplast but doesn’t compression set or pack out as easily, more durable

• used for

  • FO top covers

  • AFO padding

  • Distal end pads

Felt

• excellent padding under leather

• laminations

Neoprene Foams

• made of expanded neoprene rubber

• available covered one or two sides, one side Velcro sensitive

• good for dynamic straps

• not thermo-formable, harder to sand or grind edges

• good shock absorption properties

• good compression set properties

• excellent top cover for shoe inserts