In Sentence 2 Biomass-derived PLA is produced from renewable feedstocks such as corn and sugar cane. The writer provides background factual information for the reader. Sentence 2 is in the Present Simple tense, which is the verb tense used for accepted/established facts. Research papers often begin, either in the first sentence or the first paragraph, with accepted or established facts. This ensures that all readers have the appropriate background information to process the rest of the paper. So what kind of fact should I start with? This depends on how wide your subject — and therefore your readership — is. If your research area is very narrow, many of your readers will have a good level of background knowledge and you can start with fairly specific information. If your paper is likely to attract a wider or more interdisciplinary audience, then you should start with more general background information and even consider including background facts which seem obvious to you. You can find good examples of that first fact by checking similar papers published recently in your target journal. Note that if you resubmit the paper to a different journal, the readership of that journal may be either narrower or wider, so you cannot simply re-send the original version. In particular, you may need to adjust the first sentence to ensure that it responds to the needs of a different readership. The golden rule is: check recent editions of the journal you are submitting to, and start your Introduction in the same way as other authors who have successfully submitted their work on similar topics to that journal.