Plastics and Whitewater Boats.

Overview of plastics used in boating:

Most plastic whitewater boats are made either of ABS (Acrylonitrile Butadien Styrene), HDPE (High-Density Polyethylene), or HDXLPE (High-Density Crosslinked Polyethylene).

ABS and HDPE are both thermoplastic materials. Thermoplastics have the advantage can be welded easily. HDXLPE however has the properties of a thermoset plastic, meaning once the plastic has been molded and set it cannot be welded.

ABS is primarily used in open boats. Most closed boats are made from HDPE, some are made from HDXLPE (crosslink).

A crosslinking agent reacts with the polyethylene during molding, forming a crosslinked poly molecule similar to a thermoset plastic. This reaction improves the toughness and environmental stress crack resistance. Crosslinked polyethylene resin is NOT weldable, is it not recyclable, and it is not as easily patched or glued. The polymers used in plastics are also cross-linkable by non-chemical processess such as irradiation. (This is more useful to the medical or food industries.) So while boats made of cross-linked plastic are initially tougher, once damaged they are more difficult to repair.

Polyethylene plastics boats typically are manufactured either as rotomolded single-layer, rotomolded multi-layer, and blowmolded.

Rotomolded (rotational molding, ie, made with a rotating mold) is where plastic powder or pellets are inserted into a hot boat-shaped mold. The mold rotates and the plastic pellets melt to the surface of the mold, creating the outside layer of the boat. Multiple layers of different types (such as inner foam) can be added. When the mold cools down you have a boat. Molds can also rotate on single axis (linear lay up) or along more then one axis.

In Blowmolding, plastic is pressed through a die under high pressue and then clamped into a mold. With this method the plastic molecules are much longer then that of rotomolded boats resulting in a stronger and stiffer hull.

ABS plastic is lighter and more rigid then HDPE or HDXLPE which makes it a better material for the larger and bulkier open boats; however it is also more brittle which means open boats get damaged easier. (Some kayakers have been also heard to claim that open boats are just more likely to hit rocks; but this is a religious arguement.) ABS is also used to make things like pipes, golf club heads, toys, LEGO bricks, etc.

Open boats are typically made from a type of ABS called "Royalex". Royalex is a Uniroyal trade name for a laminate sheet with an outer layer of crosslink vinyl sandwiching solid inner ABS substrate layers surrounding an ABS form center core. The inner foam core provides rigidity as well as buoyancy while the layers of ABS sheeting give it strength (think corrugated cardbord). The outer vinyl coating composed of a PVC-Nitro-Rubber blend provides UV and abrasion protection. All the layers are all fused together by vulcanization.

Many manufacturers use different thinknesses of core, coverings, etc, for recreational boats, but thay are all "Royalex" and made by Uniroyal. Some of the other names for Royalex-like materials are Royalite and Oltonar.

Royalite is a form of ABS laminate similar to Royalex except Royalite uses an ABS core and substrate with R-84 replacing the vinyl covering. R-84 is thinner but stiffer and lighter then vinyl, which allows the ABS substrate to be thinner making the boat lighter. (Note: Some web resources claim that Royalite can have either an ABS or PVC foam center core, however Spartech says that Royalite is manufactured with only an ABS foam core.) R-84 is made from AES (Acrylonitrile-Ethylene-Propylene-Styrene).

In February 2000, the Spartech Corporation purchased the Uniroyal Royalex Manufacturing Division and the rights to manufacture Royalex and Royalite from Uniroyal. The Spartech plant in Warsaw, Indiana, now manufactures the plastic sheets used by all the major open boat companies (Esquif, Mohawk, Bell, Mad River, Whitecell, Evergreen, Old Town). (Originally I always thought Dupont made Royalex, but as far as I can tell from various web searches Dupont only makes Kevlar, not Royalex.)

Unprotected thermoplastics exposed to sunlight for an extended period of time absorb ultraviolet light (UV) which can cause discolorations, embrittlement and eventual cracking. Fluorescent light has a similar effect. Elevated temperatures can accelerate the embrittling process. (ie, If you leave your boat out in the sun, expect the hull to get brittle and easily damaged.)

Most plastics can are pigmented (colored) during rotomolding to protect the chemicals from UV exposure. For Royalex boats, the outer vinyl layer does the same thing.

Which manufacturers use which plastic?

A quick survey of different canoe and kayak manufacturers yielded the following:

Bell Canoe Works All whitewater models Royalex.
Blue Hole Canoe also Evergreen Canoe All models Royalex; some models available in either light or heavy duty Royalex layup.
Dagger Canoes (defunct) Most models were Royalex; some models were Royalite.
Dagger Kayaks Exilar Polyethylene Plastic (Exilar is a special Dagger polyethylene blend apparently. I've been told that it's basically the same as HDPE). Older kayaks (very early 90's and before) used XLPE (crosslink).
Esquif Canoe All whitewater models Royalex except for Spark (Royalite), and Taureau (HDPE).
Jackson Kayak Rumored to still be crosslink
Liquid Logic HDPE
Mad River Canoe All whitewater models Royalex; some general purpose models HDPE.
Mohawk Canoe Most whitewater models Royalex; Maxium and Rodeo models Royalite, Shaman comes either Royalex or Royalite.
Old Town Canoe Oltonar/Royalex ABS (Old Town's version of Royalex)
Pyranha HDPE
Riot Kayaks Crosslink if extra extra shiney

Weldable plastics vs non-weldable, which is which?

Weldable Plastics (common plastics used in boating listed first):

Type Chemical/Polymer Used Usage and notes:
ABS Acrylonitrile Butadien Styrene Open boat hulls.
Kydex Kydex (Acrylic-PVC Alloy) Foot pegs, misc parts.
PVC or V Polyvinyl Chloride, Type 1 Grade 1 Deck plates, gunnels, misc parts.
HDPE High Density Polyethylene Closed boat hulls.
HDLPE or LHDPE High-density Linear Polyethylene
MDPE (a.k.a. LLDPE, or LMDPE) Medium Density Polyethylene or Linear Polyethylene
LDPE Low Density Polythylene
PE Polyethylene
Acetal ?
Acrylic ?
CA Cellulose Acetate
CAB Cellulose Acetate Butyrate
Copolymer ?
CPP Copolypropylene
CPVC Chlorinated Polyvinyl
ECTFE (Halar and Tefzel) Ethylene-chlorotrifluoroethylene
Ertalyte ?
FPVC Flexible PVC
HIPS High Impact Polystyrene
HMW High Molecular Weight Polyethylene (used with UHMW)
HPP Homopolypropylene
King Starboard ?
Nylon Nylon?
PC (a.k.a. Lexan) Polycarbonate
PETG Polyethtlene Terephthalate-Glycol Modified
PP Polypropylene
PVDF (a.k.a. Kynar) Polyvinylidene Fluoride
SAN Styrene (High Impact)
Teflon ? Not recommended for hand-held welding due to high level of toxic fumes.
TPU Thermoplastic Urethane
TPUR Polyurethane
UHMW Ultra High Molecular Weight Polyethylene

Not Weldable Plastics:

Type Chemical/Polymer Used Usage and notes:
HDXLPE High-density crosslinked polyethylene
XLPE or PEX Crosslinked polyethylene
TPE Thermo Plastic Elastomer
TPPE Thermo Plastic Ester Elastomer
TPO Thermo Plastic Olefin
TPV Thermo Plastic Vulcanate
MPR Melt Processible Rubber
TPS Thermo Plastic Styrenics
F-PVC Flexible PVC
EVA Ethylene Vinyl Acetate
IR Ionomer Resin
TPU Thermo Plastic Polyurethane

Not Sure:

Type Chemical/Polymer Used Usage and notes:
PB Polybutylene
PET Polyethylene terephthalate
PS Polystyrene