Teiid has a maximum default length of 4000 for Strings [Supported Types - Teiid 8.11 (draft) - Project Documentation Editor]
However, you can override this by setting the system property org.teiid.maxStringLength [System Properties - Teiid 8.11 (draft) - Project Documentation Editor]
But be careful doing so (read the fine print).
You may want to consider creating a custom object to hold your string so that you don't expose the rest of the server possible memory issues (as mentioned in the fine print).
Hope that helps.
Using a clob type would also be appropriate.