Drawing a block arrow in latex

Question

In a block diagram, I want to connect two blocks with block arrow rather than a single arrow. Is there any LaTex command for that.

 \documentclass[10pt,a4paper]{article}
\usepackage{tikz}
\usepackage{adjustbox}
\usetikzlibrary{shapes,shadows,arrows,decorations.markings}
\begin{document}
\tikzstyle{decision}=[diamond,draw,fill=blue!50]
\tikzstyle{line}=[draw, -stealth,thick]
\tikzstyle{block}=[draw,rectangle,  text width=4.5 em, minimum height=10 mm,text centered,node distance=4 em] 
\begin{figure}[htbp]
\begin{adjustbox}{max width=0.9\textheight,center}   %% adjust max height
\begin{tikzpicture}[thick]
\node [block] (a) {A};
\node [block,right of=a,xshift=6em] (b) {B};
\node [block,right of=b,xshift=3.5em] (c) { C};
\node [block,right of=c,xshift=3.5em] (d) {D};
\node [block,right of=d,xshift=3.5em] (e) {E};
\node [block,right of=e,xshift=3.5em] (f) {Accomodating Text inside a block needed};
% ARROWS
\path [line] (a) -- (b);
\path [line] (b) -- (c);
\path [line] (c) -- (d);
\path [line] (d) -- (e);
\path [line] (e) -- (f);
\end{tikzpicture}
\end{adjustbox}
\end{figure}
\end{document}

I have two main issues:

1. Between Blocks C & D and between E & F, I want block arrow inside of the arrow obtained from the code.
2. I want long text in last block to be accommodated inside the block or oriented in the vertical direction.

Answer 1

Do you mind arrow like red one on the picture below?

 \documentclass[10pt,a4paper]{article}
\usepackage{tikz}
\usepackage[margin=25mm,showframe]{geometry}
%\usepackage{adjustbox}% <--- not needed
\usetikzlibrary{arrows,
                chains,% <--- new
                decorations.markings,
                shadows, shapes.arrows}

\tikzset{% <--- modified
    decision/.style = {diamond,draw, fill=blue!50},
        line/.style = {draw, -stealth, thick},
       block/.style = {rectangle, draw,  text width=4 em, minimum height=10 mm,
                       align=center}
        }
\makeatletter
\tikzset{suspend join/.code={\def\tikz@after@path{}}}
\makeatother

    \begin{document}              
\begin{figure}[htbp]
    \begin{tikzpicture}[thick,
          node distance = 0ex and 3em,
            start chain = A going right,
      every join/.style = {draw, -stealth, thick},
    block/.append style = {on chain=A, join}
                        ]
\node [block]   {A};% <-- A-1
\node [block,right=5em of A-1]    {B};
\node [block]   {C};
\node [block]   {D};
\node [block]   {E};% <-- A-5
\node [block,suspend join]  {Accom\-modating Text
                             inside a block needed};
\node [single arrow, draw=red, minimum height=3em, outer sep=0pt,
       right=0pt of A-5.east] {\vphantom{x}};
    \end{tikzpicture}
\end{figure}
    \end{document}

I modified your MWE with goal to make code concise as possible. For arrow I use shape single arrow from tikzlibrary shapes.arrows. An adjustbox can become a source of unexpected problems, so better solution is to accommodate node and font size accordingly. As you can see, I erase it.