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TOLEDO (SPAIN)COMPARATIVE STUDY OF MECHANICAL, RHEOLOGICAL AND
MORPHOLOGICAL PROPERTIES OF DIFFERENT CELLULOSE-REINFORCED HIGHDENSITY POLYETHYLENE COMPOSITES UPON MECHANICAL RECYCLING
C. Fonseca1, A. Ochoa1, T. Aguinaco1, C. Gonzalez2, J. Arranz-Andrés3
1GI POLCA (POLímeros, Caracterización y Aplicaciones Unidad Asociada ICTP-CSIC (Universidad Politécnica de Madrid)
2Departamento de Ingeniería Química y Tecnología del Medio Ambiente, Universidad de Oviedo, Julián Clavería, s/n.

33071-Oviedo, Spain.
3Instituto de Ciencia y Tecnología de Polímeros, ICTP-CSIC, Juan de la Cierva 3, 28006 Madrid, Spaine-mail:jarranz@ictp.csic.esAbstract
Injection molded testing specimens of original composites with different cellulose fibers composition were reprocessed up to
five cycles under the same molding conditions. Original and five-cycle reprocessed specimens finally obtained were tested
for determining their melt flow index, tensile properties and their morphology for comparison.
In this work quantitative effects of cellulosic fibers content, type of coupling agent and the number of reprocessing cycles
onto the properties of those composites were determined.

Keywords: Cellulose fibers, mechanical recycling, coupling agent.

1. Introduction
Plastic-matrix composites reinforced with several kinds ofcellulosic fibers are being object of a growing interest andintensive research for replacing other composite
materials
containing
inorganic
fillers
and/orreinforcements. This is due to the inherent advantages ofthe former ones over the latter ones, such as lower
density, lower abrasion of processing equipment, higher
specific mechanical properties, biodegradability andlower cost, among others.
On the other hand, there is also a growing social concern
regarding the environmental impact of polymericmaterials and their residues, and the sustainability of thedeveloped products. Therefore, the introduction of new
raw materials for manufacturing end-products is
subjected to specific analysis in order to analyze their
viability to be recycled. On this regard, mechanicalrecycling of polymeric materials offers significant
opportunities for their waste reduction while maintaining
both materials and energy.

2. Materials and Methods
Cellulosic fibers used as reinforcement in composites
were supplied by ENCE-Navia, a kraft pulp mill located inNavia, Asturias (Spain). They were a by-product obtainedin the manufacture of Kraft cellulose pulp, consisting ofunbleached cellulose with a cellulose content higher than
95%, and quantities of unreacted wood. The commercial
high density polyethylene (HDPE) used as polymericmatrix for composites consisted of Eraclene MQ-74
homopolymer pellets (Polimeri Europa, Milano, Italy) witha density of 952 kg/m3 (ASTM D1505) and a melt flowinteriores libro.indd 161index of 11 g/10 min measured at 190 ºC and 2.16 kg,according to ASTM D1238.
Two commercially available maleic anhydride-modified
polypropylene polymers (Epolene E-43 and G-3002)
were used as coupling agents for the referencecomposite materials (Eastman Chemical Products,Kingsport, TN, USA). Epolene E-43 has an acid numberof 45, a weight average molecular weight of 9100 g/mol,and a number average molecular weight of 3900 g/mol.
Epolene G-3002 has an acid number of 60, a weightaverage molecular weight of 60000 g/mol, and a number
average molecular weight of 20000 g/mol.
Melt flow indexes of original and five-cycle reprocessedcomposites were measured at 190 ºC and 2.16 kg,according to ASTM D1238 standard, using aDAVENPORT melt flow indexer, mod. 2233 (LloydInstruments, Farehand, UK).
Tensile modulus of elasticity of composites weredetermined according to ISO R527 standard at a nominal
strain rate of 1 mm/min and the other tensile properties
were determined at 50 mm/min using a Hounsfield
Universal Testing Machine, mod. JJ T5501 (Salfords,England). A minimum of six specimens were measuredfor each trial.
The morphology of the composites was examined using
an XL30 ESEM PHILIPS electron microscope at 25 kV.
Samples of injection molded test specimens were
cryogenically fractured in liquid nitrogen and sputtercoated with gold before viewing.

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6th International Symposium on Feedstock Recycling of Polymeric Materials

3. Results and Discussion
The variation of the melt flow indexes of cellulosic
reinforced/HDPE composites mainly depends on the fibercontent and the number of reprocessing cycles. The
relative melt flow index increase of the five-cycle recycled
composites over the original ones is higher as thecellulosic fiber content of the composites increases.
Upon reprocessing, the composites containing the E-43
maleated polypropylene showed a smoother decrease of
the tensile modulus than that containing the G-3002
maleated polypropylene, with a bigger acidity andmolecular weight than the E-43.
However, the choice of G-3002 as coupling agent derives
in a superior increase of the elongation at yield and alesser decrease in tensile strength at yield byreprocessing, in comparison with the E-43 coupling
agent.
Moreover, the influence of recycling process on theelongation at tensile strength at break is more noticeable
for composites containing the G-3002 coupling agent,
showing a higher increase in comparison with the E-43ones.
Composites without coupling agent and those containing
E-43 coupling agent carried out a lesser degradation by
reprocessing by injection than G-3002 coupling agent
composites, so indicating a possible degradation of thelater agent by mechanical recycling.

Fig. 2. Microphotography of 40 wt.% fibers and 1.5 wt%
MAPP E-43 recycling composite

4. Conclusions
Although, there has been demonstrated the advantage ofusing coupling agent in order to improve the mechanicalproperties of the original composites, it is necessary,from a recyclability point of view, to be very careful inchoosing the type of coupling agent. Otherwise, it would
be much convenient not to use coupling agent in theformulations.
Despite it is interesting the use of high content of fibers
from the economical point of view, considering recycling,a high proportion of fibers produces higher degradations
by shear effect on the composite materials. As a whole,
the formulation that carried out the highest degradation
was the 48 wt.% cellulose content one.
The best results, considering good properties for theoriginal composites and viability of recycling, wereobtained for 40 wt.% cellulose content PE composites
using the Epolene E-43 as coupling agent.
The stress-strain curves of the 40 wt.% original andrecycled composites either with or without coupling
agent, show the different behavior of these materials in
tensile tests, from a hard material for the former ones toa deformable material for the last ones.

References
Fig. 1. Microphotography of 40 wt.% fibers and 1.5 wt%
MAPP E-43 composite.
Figure 1 shows the microphotography of 40 wt% fibers
and 1.5 wt.% MAPP E-43 composite. The fibers areobserved homogeneously dispersed into the matrix.
There is not showed practically holes between fibers andmatrix, indicating that the fibers are embedded in theHDPE matrix due to an increase in the adhesion between
fibers and matrix because of the effect of the coupling
agent MAPP E-43, in comparison with the composites
without coupling agent.
On the other hand, Figure 2 shows the 40 wt.% fibers
and 1.5 wt% MAPP E-43 recycling counterpart
composite. The difficult to observe fibers is a proof of
their breakage. But some fibers and fiber residues can beobserve embedded in the matrix, with good adhesion
with the polymer in mostly of them, although there is also
some holes, indicating fiber extraction and fibers coming
out of the matrix by mechanical recycling effect.

interiores libro.indd 162[1] Arzondo, L.M., Pérez, C.J., “Injection molding of longsisal fibers reinforced polypropylene. Effects ofcompatibilizer concentration and viscosity on fibers
adhesion and thermal degradation”. Polym. Eng. Sci., 45(4), 613-621 (2005).
[2] Beg, M.D.H., Pickering, K.L., “Reprocessing of wood
fibre reinforced polypropylene composites. Part I: Effects
on physical and mechanical properties”. Composites:
Part A, 39, 1091-1100 (2008).
[3] Fonseca, C., Aguinaco, T., “Analysis of the evolutionof mechanical and thermal properties of reprocessedhigh density polyethylene”. 7th Mediterranean Congressof Chemical Engineering ,6 Barcelona, 246 (1996).
Acknowledgements
The authors are grateful for the financial support ofMICINN (project MAT2010-19883). J. Arranz-Andrés isgrateful to the CSIC JAE-Doc Program for his financial
support.

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