Sorry, Zulu, but these hypothesis have been disproved. There is no "Bioplastic coating" on the fibers... and the chemical process of fire cannot change the atomic molecular composition of the Carbon. IF either of these were true, to distort the date from the first century to the 14th, would require that the polluting factor whether bioplastic or Carbon soot, would have to outweigh the original material by 60%. It's simply not there.
There was sampling error... but the reason for the dating error is that the C14 labs tested a sample that was a mixture of older and newer material that was deliberately added to the Shroud sometime in the 16th Century.
Statistical analysis of the C14 test results of the sampleswhich were all taken from the same pieceshows that sub-sample from one end of the sample are NOT statistically the same as the sub-sample from the other end, a distance less than 1 inch apart, and that the two sub-samples could not have come from the same piece of cloth!!! Yet it is obvious that they were from the same sample. This should have been a red-flag for the testers. They ignored it... and in fact fudged their results to obscure the data.
The reason for this inexplicable statistical aberration is that the damaged original FLAXEN cloth was very skillfully, invisibly interwoven with a COTTON reweaving to repair the damaged corner where the C14 test sample was taken. The percentage of new to old material varied with distance from the center of the Shroud toward the bottom edge. The more new material found in a sub-sample the younger it tested... the more old material, the older it tested.
Another researcher has also questioned the concept that the amount of carbon 14 in the atmosphere is a constant. That individual felt that the amount present is impacted by volcanic eruptions which increase the Carbon 14 content in the atmosphere, and by extension - samples.
It also seems improbable that the Shroud, being confined in a container which was burned in a fire did not receive a fresh infusion of carbon 14 contaminant at the time of that incident.
I have also read about the errors in the sampling methods and agree with you there.
Palynological studies on the pollen indicate the Shroud spent time in area of Jerusalem. Sample of pollen taken from the Shroud area around the head of the image came from an eastern Mediterranean plant which produce wicked thorns - the type of thing the mock crown Christ had on his head may have been made from.
When you combine all this with the anatomical evidence, the inability to explain the method in which the image was made, the peculiar nature of the image, and evidence from the weave of the original Shroud material, the evidence is very compelling that this MIGHT have been the burial Shroud of Christ.