How to restrict users on deleting files from trash folder?
No, users will always be able to delete the files they own (modulo some complex ACL setups which are not feasible for a desktop).
The trash can in ubuntu is just a special subdirectory under the user's home folder, which by definition is owned by that user. Even if you change the file permissions, the user could change them back and then delete the file.
If you are trying to avoid data loss, a much better solution would be to set up automated backups - that way anything that did get deleted could be recovered.