5 One way to toughen polymers is to incorporate a layer of rubber particles5 and there has been extensive research regarding the rubber modifi cation of PLA.
Introduction — Grammar and Writing Skills 5 Later on, in the Results section, you can even decide to state your own fi ndings this way. Look at these two sentences which describe results: (a) We found that the pressure increased as the temperature rose, which indicated that temperature played a signifi cant role in the process. (b) We found that the pressure increases as the temperature rises, which indicates that temperature plays a signifi cant role in the process. Which sentence is 'stronger'? In (a), using the Past Simple tense means that your fi ndings are linked only to your own research, and you do not claim your deductions should be considered as accepted or established facts, or even that another researcher will necessarily get the same results. In (b), using the Present Simple tense means that you believe your fi ndings and deductions are strong enough to be considered as facts or truths. Th e Present Simple communicates this reliability and your readers will respond to your work accordingly. Th ere will be more about this later, in the unit on Results. Past Simple/Present Perfect Another tense pair you need in the Introduction is the Past Simple tense and the Present Perfect tense. You will need both, and you need to know when and why to switch from one to the other. Look at these sentences: (a) Past Simple: I lived in Tokyo for fi ve years... but I don't live there anymore. (b) Present Perfect: I have lived in Tokyo for fi ve years... and I still live there NOW.
(c) Past Simple: I broke my glasses... but it doesn't matter/I repaired
them. (d) Present Perfect: I have broken my glasses... and so I can't see properly NOW.