You can use the replaceAll function to strip leading zeros. This function accepts regular expressions. So, you can tell it to remove leading zeros with something like this:
replaceAll(MaterialNumber, '^0+', '')
If this is always true you could have a quick solution by parsing it to Integer, removing the leading zero’s and then back to String or Decimal*
For some documentation on the matter see:
parseInteger → https://docs.mendix.com/refguide/parse-integer
toString → https://docs.mendix.com/refguide7/to-string
I don’t know your context, but I think in this case it is not bad to add a “technical” integer attribute to your entity like _MaterialNumber. The value of this attribute is your material number parsed to an integer (use the function parseInteger).
Consider to use an event like an OnChange to set the _MaterialNumber attribute value correctly. So you have no need to do this for each display (better performance). In your view you can use _MaterialNumber to show without leading zeros. And you still have the original attribute available.