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@PHDTHESIS{Wei:1009668,
author = {Wei, Yanfeng},
othercontributors = {Möller, Martin and Pich, Andrij},
title = {{H}ydrophobically modified polyvinylamines to apply
exfoliated clay in organic media},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2025-03603},
pages = {1 Online-Ressource : Illustrationen},
year = {2025},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen University, 2025},
abstract = {Clay minerals are desirable nanoparticle reinforcements for
polymers in order to produce inexpensive, lightweight
nanocomposites with exceptional performance due to their
unique layered structure, rich intercalation chemistry and
affordable availability. The unique stacking distribution of
the charged layers creates the possibilities to construct
nanocomposites by interacting with organic functional
groups1-10. Better than conventional microparticle
composites, the properties of the intercalated and
exfoliated nanocomposites are more synergistic if which the
clay platelets are entirely and uniformly dispersed in a
continuous polymer matrix. Nacre mimetic nanocomposites with
a maximum fraction of clay particles, are among the mostly
explored. The unique brick-and-mortar structure of nacre
causes a great increase in mechanical properties(tensile
stress, modulus). The incorporation of inorganic
reinforcements with only a small fraction (less than $5\%)$
of the soft component promotes proper frictional sliding
between the platelets and forms sacrificial bonds, thereby
contributing to an overall enhancement in mechanical
performance. However, it should be noted that the existing
clay/polymer nanocomposites often contain only lower
proportions of clay particles with only partly exfoliated or
intercalated structures. The properties of such artificially
manufacture nanocomposites are far from reaching the
characteristics exhibited by natural nacre materials. To
produce high-quality nanocomposites, it is imperative to
enhance the homogeneity and therefore the mixing of clay
minerals and polymers. One of the major challenges in this
study is mitigating the inherent hydrophilic nature of the
clay minerals. The pronounced hydrophilicity of clay
presents challenges in attaining homogeneous composites when
using hydrophobic matrix polymers. Hence, for organic
polymers improving the hydrophobicity of the exfoliated
clays is crucial for the formation of such nanocomposites
and to avoid unfavourable changes of their properties when
exposed to higher moisture conditions. However, in the
pursuit of ordered and homogeneous composites, the
hydrophilic nature of clay minerals necessitates the use of
water as the exfoliation medium, in conjunction with
water-soluble polymers. PVAm possesses the highest
concentration of pendant primary amine groups, thereby
providing a large number of reactive sites for subsequent
modifications. Herein, hydrophobically modified
polyvinylamides were prepared and interacted with different
synthetic clays, i.e., Laponite®, Sumecton® SWF to create
nacre mimetic nanocomposites. The incorporation of
hydrophobically modified polyamides into clay minerals
effectively mitigates their water sensitivity. At the same
time, the amine groups present in the partially modified
polyvinylamides facilitate improved compatibility between
clay minerals through interactions with the oxygen surface
via cation exchange reactions. Chapter 2 presents a concise
overview of the crystal structure of clay minerals,
providing a comprehensive understanding of the intercalation
and exfoliation processes. It also explored the applications
and properties of nanoclay composites, along with the
manufacturing procedures involved. Furthermore, the chapter
introduced PVAms, encompassing their distinctive synthesis
technique, diverse functional capabilities, and broad range
of applications. Chapter 3 has been dedicated to the
synthesis of copolymer of vinylformamide and vinylamine and
the hydrophobic modifications by N-benzylation and
N-octylation. Benzyl, alkyl, and mixed functional groups
were introduced by adjustable functionalization degrees. The
research investigated the solubility of the modified
polymers in both water and various organic solvents.
Additionally, the study compared the surface tension between
toluene and differently functionalized polyvinylamides in
aqueous solutions. The polymers were combined with
Laponite® (LAP) in varying feed ratios to assess the impact
of LAP content and the functionalization degree on the
homogeneity in the composites. Notably, composites of LAP
and a mixed functionalization polyvinylamides exhibited the
most desirable homogeneity among all samples. Based on the
findings, the LAP/(modified polyvinylamides) at 90/10 w/w
ratio was determined to be the optimal composition due to
the homogeneous and transparent appearance exhibited by the
composite at this ratio.Chapter 4 provides enhanced
investigations of the preparation of nanoclay composites,
focusing on the novel synthesis of modified
poly(vinylacetamide-vinylamine) copolymers. Furthermore,
this chapter explores the application of these modified
polymers in conjunction with clay minerals LAP® and
Sumecton® SWF (SWF). The presence of acetamide groups
imparts increased hydrophobicity of modified
P2-PVAms/P3-PVAms, promoting solubility and enhancing
compatibility of modified polymers with clay even in alcohol
solvents and for highly functionalized P3-PVAm. Based on the
findings from Chapter 3, the optimal composite ratio of
clay/ (modified P2-PVAm/P3-PVAm) was determined to be 90/10
w/w. The long alkyl chains were found to be more effective
in facilitating the formation of homogeneously arranged
layers of nanoplatelets. Cryo-FESEM was employed to directly
investigate the distribution of layers in nanocomposites in
the form of slurries. The morphology of the supported films
was examined using stereomicroscopy and polarized optical
microscopy. Water resistance was evaluated through the IGA
adsorption technique and by immersing the supported films in
water. The results revealed that a combination of factors,
including the increased aspect ratio of clay minerals, high
functionalization degree of the modified polymers, and the
uniform arrangement of nanoplatelet layers in the
composites, collectively contributed to maintaining the
structural integrity of the supported films when submerged
in water. The composites were redispersed in alcohol
solvents to mitigate the impact of humidity sensitivity and
crack formation resulting from the film preparation process
under higher moisture conditions. The results demonstrated
that high functionalization of N-dodecylated P3-PVAm and the
homogeneous arrangement of nanoplatelet layers within the
composites significantly enhanced the transparency and
flatness of the supported films, resulting in improved water
barrier properties. Although the film obtained by recasting
from an ethanol solution exhibited a certain degree of
opacity due to the comparatively low degree of
functionalization of N-dodecylated P3-PVAm (only $31\%),$ it
showed improved water barrier properties. This improvement
could possibly be due to the homogeneous arrangement within
the composite. The opaque film comprised of
LAP/(N-dodecylated P3-PVAm) exhibited structural integrity
for a minimum of 5 days when immersed in water.
Additionally, the transparent supported film of the
SWF/(N-dodecylated P3-PVAm) composite, which was recast from
an ethanol solution, retained its structural integrity for a
minimum of 8 days when immersed into water. These findings
highlight the potential application of clay composites in
environmental waterproof coatings, food packaging, and other
related areas.},
cin = {154610 / 150000 / 416105},
ddc = {540},
cid = {$I:(DE-82)154610_20140620$ / $I:(DE-82)150000_20140620$ /
$I:(DE-82)416105_20210623$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2025-03603},
url = {https://publications.rwth-aachen.de/record/1009668},
}
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