Late 1995 marked the introduction of polyurethane coated fabric (PCF) into the General Aviation life raft market in the U.S. by RFD (It's been available on the marine market for some time). BFGoodrich, RFD and Air Cruisers have also opted for this type fabric for their new rafts. This material offers some potential advantages over traditional neoprene rubber.
The manufacturers claim extended service life for the material which has the potential of saving consumers money. Other advantages, such as increased abrasion and puncture resistance, provide an extra margin of protection that is nothing to sneeze at.
On the down side, the PCF used in these aviation life rafts is all single coated, meaning the poly coating is applied to only one side of the nylon fabric substrate. Marine life rafts using this material use double coated fabric. The single coating can compromise the raft's integrity under some conditions. RFD fabricates the raft with the coated side out (with some non-air-retaining exceptions), BFG and Air Cruisers with the coated side on the inside. The coating provides the air seal. If the coating is damaged, the air can leak out. However, the coating also provides virtually all the abrasion and puncture resistance, while the nylon substrate provides most of the material's strength.
I solicited samples of the fabric used in the buoyancy tube(s) and canopy from the participating manufacturers in the second evaluation. I also asked for proof that the fabrics conformed to the TSO C70a performance and flammability requirements. All supplied the requested fabric, but BFGoodrich declined to provide conformity documentation, claiming their specification was proprietary information. Winslow and RFD supplied shipping invoices from the fabric manufacturers which included statements of conformity. While I am pretty confident that BFGoodrich's material meets the specifications, it is ironic that they wouldn't provide substantiation, since they were the ones who raised the question of material conformity in the first place during conversations prior to the testing.
In order to test the manufacturers' claims of better puncture and abrasion resistance of PCF vs. traditional neoprene coated fabric, I tested the buoyancy tube fabric samples. Lacking access (due to financial constraints) to any sophisticated laboratory where I could take appropriate measurements, I chose to use some practical tests that would show up any significant advantage, as are claimed, but might not show up minor differences.
To measure puncture resistance, I put test samples under very light tension and manually attempted to puncture and slice the fabric using a large fish hook (puncture) and a knife (puncture and slice). Without any doubt, the PCF was noticeably more difficult to puncture compared to traditional fabric, provided it was tested from the coated side. When tested from the uncoated side, as used by BFGoodrich and Air Cruisers and, in some instances, by RFD, there was noticeably less resistance to puncture, about equal to or, perhaps, just slightly better than traditional fabric. When we tested by slicing, the coated side of the PCF was also a superior performer by a large margin. However, when tested from the uncoated side, it was very easy to slice through the single layer substrate, far easier than with the traditional material which is coated on both sides. This is especially significant since the substrate is responsible for a significant portion of the tensile strength of the material. This type of utilization, with the uncoated side subject to abuse and the elements, would appear to negate some of the advantages PCF offers, depending upon where and how it is used.
To test abrasion resistance, I used 180 grit sandpaper with a convex sanding block to see how much effort and pressure was necessary to go through the fabric. The PCF was considerably superior in these tests when tested from the coated side. On the other hand, compared to traditional fabric, it was far easier to go through the substrate when tested from the uncoated side.
I was not able to test PCF at temperature extremes. However, it's use in slide rafts for transport category designs (with an aluminized exterior coating to reflect heat from a fire) would seem to indicate that it has acceptable performance, though I have no way of knowing how it compares to traditional material which performs adequately.
For the year 2000 test we had developed a bit more objective and scientific testing apparatus to test puncture and abrasion resistance in order to deal with the diverse types of marine life raft fabrics and the marine manufacturers' conflicting claims. We again requested fabric samples of those participating. Winslow supplied samples of their neoprene fabric, but both Air Cruisers and BFGoodrich, using lightweight PCF, declined, as did Hoover using neoprene. Both Air Cruiser's Wigert and Leibert Danielson, Director of Engineering at BFGoodrich, expressed similar concerns, that consumers would not be able to make value judgements regarding the relative importance of the materials' performance in our tests versus the light weight of their products. As a consumer, you'll need to make a value judgement about that response. Since our tests were to be comparative in nature, not absolute values, we have no meaningful results to report.
My conclusion is that how the material is used affects just how much advantage might be gained by using PCF. A significant amount of the performance advantage would seem to be lost when used with the uncoated side out, as done by BFGoodrich and in some places by RFD, and it might even result in some amount of performance deficit. When used with the coated side out, any damage to the coating will result in an air leak as there is no other air retention capability. This can be caused by external causes or by ripping off of some attachment, such as a fitting, which removes some of the coated material as well. These same problems would not be a concern if double-coated PCF was used, but then it would be much heavier, which is why it isn't. As for the traditional material, it is a known quantity and dependable, if not on the leading edge. EAM, Hoover, Survival Products and Winslow currently build rafts only of traditional neoprene materials. While I believe that double coated PCF, with a poly coating on both sides, which is used on some marine rafts may be quite acceptable, I have some concerns over the use of single coated PCF for life rafts.
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