John has given you some really good suggestions for finding the scientific papers that you need for this project. You need to find any scientific source of information that will help you learn more about your subject, and use as a basis for designing your experiment. John is correct; a university library would be the best place to find the complete articles.
And Jacobie has also brought up a good point about the class assignments. Your teacher wants you to go through the process of finding pertinent background information for your project. You need to understand the scientific principle behind your project and usually a good science textbook will provide that information. But you also need recent scientific articles for specific details, and also to give you an idea of how to set up an experiment that will give you measurable results.
Here is an example of how you can proceed. First, do an internet search for "Google scholar," and then type in your search terms, for example "incineration of plastic." This will bring up a list of scientific articles with no commercials. Unfortunately, as John has pointed out, most of the complete articles are not available, but reading the abstracts should be helpful and you should be able to find some complete articles to read.
Here is an abstract that describes the design of a new machine that will pull up plastic mulch from a soil bed of strawberry or pepper plants and incinerate it. Please note that the project was not successful and the machine method did not improve manual methods of plastic mulch removal. So this would be a great topic for you to investigate. It's a problem that still needs to be solved. Perfect subject for a science project!http://www.tandfonline.com/doi/abs/10.1 ... 8v06n01_03
Here is an abstract that includes the tables and figures from the paper. This research report describes a research project that optimized the dehydrochlorination of plastic as it is incinerated. This is an interesting chemistry problem. Please note the data included in the graphs. This is the type of measurable result that you need for your project board. http://www.sciencedirect.com/science/ar ... 7098001247
And here is an article that you can download and see all of the details. This was an investigation on the incomplete combustion of plastic waste as it is incinerated in a kiln. Please note the detailed protocol in the article. The primary purpose of this article is to describe a method for measuring the problem, but the authors do not offer a solution to the problem of incomplete combustion of the plastics. Again, this is another problem that needs to be solved by additional scientific research, perhaps in your science project. http://www.tandfonline.com/doi/pdf/10.1 ... 7.10466202
I hope these examples will give you a good idea on how to proceed. You have not explained exactly what problem you are trying to solve, so please let us know what you want to do.