Received: 7 October 2017 Revised: 19 December 2017 Accepted article published: 26 December 2017 Published online in Wiley Online Library: 13 February 2018
(wileyonlinelibrary.com) DOI 10.1002/pi.5524
Fabrication of sintered porous polymeric
materials: eﬀect of chain interdiﬀusion time on
Meysam Salari and Gholamreza Pircheraghi
In this study, sintered porous polymeric materials made of high density polyethylene (HDPE) werefabricated through controlling
the chain interdiﬀusion time at the transition temperature of semicrystalline and melt states. At this intermediate state, where
both crystalline and amorphous phases coexist, the interfacial welding of HDPE particles is facilitated thanks to interdiﬀusion
caused by chain relaxation phenomena. Then, by assuming a spherical shape and a cubic packing conﬁguration of particles, a
geometrical model was developed to predict porosity variations as sintering progresses. Moreover, the HDPE used, as a broad
molecular weight distributed polymer, has diﬀerent family chains with diﬀerent speciﬁc molecular weight ranges. Accordingly,
the melt coalescence rate of the particles was tracked using an optical microscope equipped with a hot stage, in order to
determine the diﬀusion characteristic times for each family. During the characterization stage, SEM images proved the presence
of porous structures in the sintered samples. In addition, mechanical properties were assessed through the shear punch test.
It was shown that the mechanical properties are governed by the interdiﬀusion of long chains which occurs at relatively long
sintering times. The results also demonstrated the role of reptation motion of long chains in the interfacial welding of polymeric
particles. They revealed the compatibility of macroscopic properties of the samples and chain motions at microscopic levels.
© 2017 Society of Chemical Industry
Supporting information may be found in the online version of this article.
Keywords: chain interdiﬀusion; sintering; HDPE; broad molecular weight distribution; porous structures
Chain interdiﬀusion across the interface of polymeric particles
occurs during the sintering process and can lead to interfacial
welding and coalescence of the polymeric particles. This mech-
anism has been the subject of many studies over past decades,
and multiple theories describing it have been proposed mainly
based on de Gennes’ reptation theory.
It is also known as
a solution widely used to overcome the processing challenges
of viscous polymers, for instance ultrahigh molecular weight
Throughout this method, the powders are ﬁrst
densiﬁed according to the polymer characteristics and then the
sintering process continues until the desired temperature and
pressure are achieved. It is notable that under this desirable
condition particles are joined and interfaces are formed. Subse-
quently, recrystallization during sintering which occurs at newly
formed interfaces results in interfacial welding and mechanical
Extensive experimental studies concerning the sintering of poly-
meric powders, mainly funded by rotational molding industries,
have been performed in order to increase the density, minimize
the porosity and maximize the mechanical strength.
studies are performed at temperatures well above the polymer
melting point, where transformation of the crystalline state to a
fully amorphous state is carried out to ﬁll empty spaces between
particles, which are considered as defects. However, the fabrica-
tion and molecular microstructure of porous polymeric materials
through the sintering process have not been investigated, and no
mechanism for this purpose has been proposed.
In this study, sintered porous samples made of broad molec-
ular weight distributed high density polyethylene (HDPE) were
fabricated and characterized by controlling the sintering time.
Thereupon, by assuming a simple cubic conﬁguration for the HDPE
particles, it was attempted to develop a geometrical model to
predict changes in porosity as a function of sintering neck radius,
which is derived from the intrinsic viscoelastic characteristics of
the polymer used.
Developing a geometrical model
As illustrated in Fig. 1(a), the sintering progress of polymeric pow-
ders with an average initial radius a
where x is the radius of the interface between two particles and
is the ﬁnal radius of the resulting coalesced particles; thus x/a
changes from 0 to 1, indicating that no sintering occurred and per-
fect coalescence, respectively.
Correspondenceto:GPircheraghi,Polymeric Materials Research Group (PMRG),
Department of Materials Science and Engineering, Sharif University of Technol-
ogy, Azadi Ave, Tehran, Iran. E-mail: firstname.lastname@example.org
Polymeric Materials Research Group (PMRG), Department of Materials Science
and Engineering, Sharif University of Technology, Tehran, Iran
Polym Int 2018; 67: 422–430 www.soci.org © 2017 Society of Chemical Industry