\begin{thebibliography}{1}

\bibitem{gmi}
{Global Market Insights}.
\newblock High density polyethylene (hdpe) market size.
\newblock
  \url{https://www.gminsights.com/industry-analysis/high-density-polyethylene-HDPE-market},
  2017.
\newblock [Online; accessed 20-May-2018].

\bibitem{fig1}
Thorsten Graunke, Katrin Schmitt, and J~Wöllenstein.
\newblock Organic membranes for selectivity enhancement of metal oxide gas
  sensors.
\newblock 2016:1--22, 01 2016.

\bibitem{pubchem}
{National Center for Biotechnology Information}.
\newblock Pubchem compound database; cid=6325.
\newblock \url{https://pubchem.ncbi.nlm.nih.gov/compound/6325}.
\newblock [Online; accessed 20-May-2018].

\bibitem{nzmfg}
{New Zealand Institute of Chemistry}.
\newblock The manufacture of polyethylene.
\newblock
  \url{https://web.archive.org/web/20180223141558/http://www.nzic.org.nz/ChemProcesses/polymers/10J.pdf}.
\newblock [Online; accessed 23-May-2018].

\bibitem{macrog}
{Polymer Science Learning Centre}.
\newblock Polyethylene.
\newblock \url{http://www.pslc.ws/macrog/pe.htm}.
\newblock [Online; accessed 23-May-2018].

\bibitem{wiki:xxx}
{Wikipedia contributors}.
\newblock High-density polyethylene --- {Wikipedia}{,} the free encyclopedia.
\newblock \url{https://en.wikipedia.org/wiki/High-density_polyethylene}, 2018.
\newblock [Online; accessed 20-May-2018].

\end{thebibliography}
