A	frequency factor in the kinetic model of viscosity reduction [Pa${}^{-0.3}$ · s${}^{-1.3}$]
$C_p$	heat capacity of resin [J/(kg·K)]
D	inner diamenter of the barrel [m]
E	activation energy of thermal decomposition [J/mol]
f	fill ratio [-]
H	height of the screw channel [m]
k	reaction rate of thermal decomposition [1/s]
l	length of the die [m]
$L_p$	path length of the screw [m]
$L/D$	ratio of total length of screw to inner diameter of barrel in an extruder [-]
n	exponent in the Cross model [-]
$n_{\mathcal{N}}$	number of polymers with $\mathcal{N}$ number of nodes [-]
N	screw rotational speed [1/s]
$\mathcal{N}$	number of nodes of a linear polymer [-]
$\overline{\mathcal{N}}$	number average degree of polymerization [-]
$\mathit{Nu}$	average Nusselt number [-]
${\mathit{Nu}}_z$	local Nusselt number at z [-]
p	pressure of resin [Pa]
q	heat flux [W/m${}^2$]
Q	flow rate [m${}^3$/s]
r	radial coordinate of the die [m]
R	radius of the die [m]
$R_g$	gas constant = 8.31 J/(mol · K)
S	cross-sectional area of the screw channel or die [m${}^2$]
t	time [s]
T	temperature of resin [K]
$T_b$	barrel temperature [K]
$T_f$	exit temperature of the high-shear extruder [K]
$T_r$	reference temperature [K]
$T_w$	temperature of the die [K]
$T_{\ast }$	model parameter of the zero-shear viscosity [K]
$v^z$	z-component of the fluid velocity [m/s]
V	velocity of the barrel with respect to an observer on the screw [m/s]
$V^z$	z-component of V [m/s]
W	width of the screw channel [m]
x	coordinate of the channel width direction of the screw [m]
X	weight fraction in TGA analysis [-]
y	coordinate of the channel depth direction of the screw [m]
z	coordinate for down-channel direction or axial direction of the screw [m]
$\alpha$	pressure gradient [Pa/m]
$\beta$	heating rate in TGA analysis [${}^{\circ }$C/min]
$\dot{\gamma }$	shear rate of resin [1/s]
$\eta$	non-Newtonian viscosity of resin [Pa·s]
${\eta }_0$	zero-shear viscosity in the Cross model [Pa·s]
${\eta }_r$	zero-shear viscosity at $T_r$ [Pa·s]
${\eta }_{rf}$	value of ${\eta }_r$ at the exit of the high-shear extruder [Pa·s]
$\kappa$	thermal conductivity of resin [W/(m·K)]
$\rho$	melt density of resin [kg/m${}^3$]
$\tau$	shear stress of resin [Pa]
${\tau }_{\ast }$	characteristic shear stress in the Cross model [Pa]
$\varphi$	screw angle [rad]