Poly-Paper: A Sustainable Material for Packaging, Based on Recycled Paper and Recyclable with Paper

Abstract

Background:
Until now, environmental sustainability issues are almost entirely unsolved for packaging materials. With the final aim of finding materials with a single recycling channel, cellulose fiber/poly(vinyl)alcohol composites were investigated.

Methods:
After extrusion and injection molding, samples of composite with different cellulose fiber content (30%, 50% and 70% w/w) were tested.

Results:
Tensile mechanical tests exhibited an improvement in composite stiffness when the reinforcement content was increased together with a decrease in composite elongation. Solubility tests performed at room temperature and 45°C showed different behavior depending on the water-resistant film applied on the composite (50% cellulose fiber content). In particular, the uncoated composite showed complete solubility after 2 hours, whereas at the same time point, no solubility occurred when a non-water-soluble varnish was used.

Conclusions:
The proposed composites, named Poly-paper, appear to warrant further investigation as highly sustainable packaging.

Full text

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J Appl Biomater Funct Mater 2016; 14(4): e490-e495
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ORIGINAL RESEARCH ARTICLE
sustainable packaging should have a single separate collec-
on and recycling channel.
There is no doubt that taking eecve steps in view of pack-
aging sustainability will imply using a single material, or rather
materials with dierent properes and funconal performance
but with the same recycling channel. The above consideraons
led to our interest in developing a composite material charac-
terized by high environmental sustainability (1).
Paper and board can best sasfy these needs: recycling of
corrugated board, newspapers and magazines has been cus-
tomary for some me now, even before the term recyclable
became so popular. Sustainability is ensured by the fact that
recycling simply requires placing the discarded parts in the
paper-and-board bins available close to our homes. However,
recycling of our new material alongside the waste paper col-
lected for recycling required using a water-soluble matrix. We
chose polyvinyl alcohol (PVA), a polymer-based material pro-
duced without diverng ferle lands from agriculture, cap able
of melng in water and forming nontoxic composites (2, 3).
We called this material poly-paper. Poor resistance to water
due to the water-soluble matrix is obviously not an issue in
this case, because the resistance of Poly-paper to water (which
varies according to temperature) is anyway greater than that
of corrugated board.
DOI: 10.5301/jabfm.5000335
Poly-paper: a sustainable material for packaging, based
on recycled paper and recyclable with paper
Barbara Del Curto1,2, Nadia Barelli1, Mauro Profaizer3, Silvia Farè1,2, Maria Crisna Tanzi2, Alberto Cigada1,2,
Giulia Ognibene4, Giuseppe Recca5, Gianluca Cicala2,4
1 Department of Chemistry, Materials and Chemical Engineering “Giulio Naa”, Politecnico di Milano, Milan - Italy
2 UdR Consorzio INSTM, Florence - Italy
3 Ghel Ondula spa, Buglio in Monte, Sondrio - Italy
4 Department DICAR, University of Catania, Catania - Italy
5 CNR-IPCB, Catania - Italy
Introducon
Popular packaging materials today involve unsolved en-
vironmental sustainability issues. The main reason is that
packaging is, in most cases, made of mulple materials (cor-
rugated board, polystyrene foam, polyethylene etc.), which
are oen disposed of unsorted. Consider the packaging of a
TV set or any other home appliance: It includes corrugated
board for the outer case, polystyrene foam for inner lling,
bubble polyethylene wrap and sundry plasc parts. Each of
these materials has a dierent recycling channel (oen a
complicated one, as in the case of polystyrene foam). Truly
ABSTRACT
Background: Unl now, environmental sustainability issues are almost enrely unsolved for packaging materials.
With the nal aim of nding materials with a single recycling channel, cellulose ber/poly(vinyl)alcohol compos-
ites were invesgated.
Methods: Aer extrusion and injecon molding, samples of composite with dierent cellulose ber content
(30%, 50% and 70% w/w) were tested.
Results: Tensile mechanical tests exhibited an improvement in composite sness when the reinforcement con-
tent was increased together with a decrease in composite elongaon. Solubility tests performed at room temper-
ature and 45°C showed dierent behavior depending on the water-resistant lm applied on the composite (50%
cellulose ber content). In parcular, the uncoated composite showed complete solubility aer 2 hours, whereas
at the same me point, no solubility occurred when a non-water-soluble varnish was used.
Conclusions: The proposed composites, named Poly-paper, appear to warrant further invesgaon as highly
sustainable packaging.
Keywords: Cellulose ber, Composite, Polyvinyl alcohol, Solubility, Tensile strength
Accepted: October 18, 2016
Published online: November 1, 2016
Corresponding author:
Prof. Barbara Del Curto
Diparmento di Chimica
Materiali e Ingegneria Chimica “Giulio Naa”
Politecnico di Milano
Via Mancinelli 7
20131 Milano, Italy
barbara.delcurto@polimi.it

Del Curto et al e491
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A study by Zhang et al (4) focused on the inuence of the
chemomechanical treatments of cellulose on the physico-
chemical properes of a cellulose/PVA composite material
with 23% cellulose. The improvement of tensile strength and
elongaon has been shown to be a funcon of the decrease
of the size of cellulose bers, and was correlated with the
combined expansion of the specic surface area of the laer,
due to the increase of the grinding cycles that cellulose bers
undergo before mixing and extrusion with PVA.
In a study by Kaushik et al (5), cellulose bers were added
to a thermoplasc starch matrix (TPS), and mechanical prop-
eres were shown to improve as a funcon of the increase
of the cellulose nanobers, at a maximum demonstrated
15% rate. Huda et al (6, 7) showed that recycled news-
paper bers can be used as reinforcements in poly(lacc
acid) (PLA) and polypropylene (PP) in place of talc. In a dif-
ferent paper, Huda et al (8) postulated the use of recycled
newspaper bers as a replacement for glass bers. The
economic and environmental advantages of using newspa-
per-derived ber were outlined. In a recent study, Serrano
et al (9) demonstrated the technical feasibility of the use
of newspaper bers over glass bers for the producon of
products such as doors, windows, furniture and automove
interior parts.
The aim of the present study was to invesgate novel for-
mulaons using signicantly higher rates of cellulose to ensure
easy recycling in water of the biocomposite. Furthermore, an-
other purpose of the work was to assess the feasibility of the
developed formulaon to be used as a novel soluble material,
Poly-paper, for processing using the fused deposion modeling
technique.
Materials and methods
The polymer selected as matrix was an experimental
formulaon based on water-soluble PVA with degree of
hydrolysis between 75% and 90%, average molecular weight
(Mw) between 75 and 150 kDa and a polydispersity index
(Mw/Mn) between 2.5 and 4.3. The cellulose bers selected
as reinforcement had dimensions lower than 45 μm (>45 μm
0%-0.1%), and bulk density in the range of 232-248 g/L. All
materials were vacuum dried at 50°C for 48 hours prior to
processing.
Specimen preparaon
Composites were melt blended in a corotang twin-
screw extruder (Lab-Compounder KETSE 20/40D EC; Braben-
der, Duisburg, Germany). The extruder line was equipped
with a side feeder (MT1-12; Brabender) to feed powder
directly into the melt and a volumetric feeder (DRS28) to
feed the pellet into the extruder barrel. The sequence of
compounding was as follows: modied PVA pellets were
fed through the input hopper with the volumetric feeder;
nally the cellulose was dosed from the extruder opening
side with the side feeder. The temperature paern of the
extruder was 190°C-190°C-195°C-195°C-190°C-190°C-180°C
from input to output zones. The composites were pellezed
from the extruded lament, to be processed by injecon
molding. Composites pellets were dried (24 hours at 50°C
under vacuum) before injecon molding. From all compos-
ites, pellet dog bone specimens with dimensions according
to ASTM D638 were fabricated using a 12 mL microinjecon
molder (DSM Xplorer) at 190°C melt temperature and 60°C
mold temperature with injecon and holding pressure of
16 bar. The specimens were allowed to cool in the mold for
5 minutes before extracon. This allowed us to obtain homo-
geneous and strong postextrusion materials with cellulose
ber rates ranging from 30% to 50% (Fig. 1B, C). As shown,
without bers, the post-extrusion modied PVA only matrix
had a thin texture (Fig. 1A), and became unsubstanal with
70% cellulose bers (Fig. 1D).
The possibility to obtain laments by extrusion was nally
explored by checking, with posive results (data not shown),
whether the material could be used to produce pellets (Fig. 2)
in view of injecon molding.
Fig. 1 - Extrusion tests on: (A) modied polyvinyl alcohol (PVA) alone, (B) modied PVA + 30% cellulose bers, (C) modied PVA + 50%
cellulose bers, (D) modied PVA + 70% cellulose bers.

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Experimental characterizaon techniques
Thermal stability of cellulose bers was studied using a
TGA-500 V6.7 instrument (TA Instrument), coupled with TA
Instrument Explorer operang soware. The analyses were
performed under dynamic heang condions, from 50°C to
800°C under nitrogen ow (60 ml/min), at a heang rate of
10°C/min, using about 2 mg of sample. Data recorded show
the thermal behavior of cellulose bers in terms of weight
loss percentage increasing the test temperature.
The morphology of the dried cellulose bers was observed
by EVO Scanning Electron Microscope (Zeiss, Cambridge, UK)
at room temperature. The bers were stuck on the sample
stub. The samples were gold spuered up to a thickness of
20 nm by means of a Emitech K-550 spuer coater (Emitech,
Ashford, Kent, UK). An accelerang voltage of 15 kV was
used to collect the micrographs. The surface of the tensile-
fractured specimens was also analysed aer gold spuering.
The same observaon condions used for the dry bers were
used to analyze composite samples.
Tensile properes of the injecon molded specimens were
measured by using an Instron 5985 universal tesng machine,
equipped with a load cell of 10 kN in accordance to ASTM D638
standard. The tensile specimens had a length, width and thick-
ness of narrow secon of 165, 13 and 3.2 mm, respecvely.
These dimensions are in accordance with specimen Type I as
reported in the ASTM D638 standard. Five specimens were
tested for each composite, with a constant speed of 5 mm/min,
while compliance correcon was used. System control and
data analysis were performed using Instron’s Blue Hill soware.
The ability of the composite material (with 50% cellulose
ber) to melt by soaking with water was then evaluated by
simulang maceraon condions. Briey, tests were per-
formed on specimens (40 × 40 × 5 mm), both at room temper-
ature and at 45°C. Some specimens were supercially coated
with a varnish lm to check for possible water resistance of
the material in view of specic applicaons.
Results and discussion
Characterizaon of cellulose bers
Thermal stability of the cellulose bers was invesgated
by thermogravimetric analysis (TGA) under nitrogen ow. In
Figure 3, the TGA result for dried cellulose ber is reported.
The TGA curve showed 3 thermal degradaon steps ranging
from 200°C to 800°C. In parcular, the rst degradaon step
at 267°C was due to the degradaon of cellulosic substances,
such as hemicellulose and cellulose. The second degradaon
(T = 383°C) of the decomposion was related to the degrada-
on of noncellulosic materials in the bers, while, the nal
degradaon steps between 620°C and 800°C were due to mi-
nor components in the bers. The residual char accounted for
19% of the inial weight. The thermal stability of the cellulose
bers up to 267°C ensured the processability of the compos-
ites up to 195°C which was the maximum selected tempera-
ture in the extruder for compounding.
The morphology of the cellulose ber obtained by the pa-
per recycling process was invesgated with SEM (Fig. 4). The
recycled paper appeared in a brillary form, with bers rang-
ing from 50 to 200 µm. The surface of the brils appeared
rough probably due to the recycling method used.
Tensile properes of the composites
The tensile properes of the modied PVA/cellulose compos-
ites were compared with neat modied PVA. The stress–strain
Fig. 2 - Poly-paper pellets obtained by extrusion.
Fig. 3 - Thermogravimetric analysis curve for the cellulose bers.

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Fig. 4 - SEM images of the dried cellulose ber from recycled paper: (A) ×300 magnicaon (scale bar: 100 μm); (B) ×1,000 magnicaon
(scale bar: 20 μm).
curves of the neat modied PVA and of the composites are re-
ported in Figure 5. The stress–strain curves showed a necking
extension for the neat modied PVA sample. The yield stress for
the composites decreased slightly with increasing the cellulose
ber content. The tensile modulus showed sharp increases with
tensile modulus varying from 3.57 to 5.19 and 7.17 GPa, with an
increase of 45% and 101% for the composites with 30 wt% and
50 wt% of cellulose, respecvely (Tab. I). This indicates that the
stress would be expected to be transferred from the polymer
matrix to the stronger cellulose ber, indicang also a good in-
terfacial adhesion. Similar results were obtained by Huda et al (6)
with the addion of 30 wt% recycled newspaper bers to PLA. In
addion, the mechanical properes here obtained were in the
range of, or even higher than, those reported by Graupner for
PLA-reinforced composites for use in the automove sector (10).
In addion, the use of natural or recyclable constuents makes
the composites studied interesng as environmentally friendly
materials (11).
The tensile-fractured surface of the specimens consid-
ered was analysed by SEM (Fig. 6). Neat PVA (Fig. 6A) showed
a rough surface, conrming the mechanical data for a duc-
le behavior, while the surface appeared less rough for the
sample modied with 30 wt% cellulose bers (Fig. 6B). The -
bers were covered by matrix in both of the samples at 30 wt%
(Fig. 6B) and 50 wt% (Fig. 6C, D). However, in the sample with
50 wt% of bers, the higher ber volume fracon resulted in
a more complex surface topology.
Stability test
The stability tests showed that the composite mate-
rial (Fig. 7) was completely dissolved within about 2 hours
when uncoated (cellulose 50 wt% in Fig. 7) and coated with
2 dierent percentages (3.3% and 10%) of ketone-aldehyde
resin. When the composite was coated with a varnish, either
non-water-soluble or water-soluble, the coated composite
specimens showed good stability up to the end of the test.
The obtained results showed that if appropriately coated,
Fig. 5 - Representave tensile stress–strain curves of the composites:
neat polyvinyl alcohol (PVA) (A), and PVA/30 wt% cellulose bers (B).
the composite can be stable for a longer me, hence it can
be used also in an environment with a high percentage of
humidity.

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TABLE I - Mechanical parameters obtained in the tensile characterizaon test performed on the composites reinforced with dierent per-
centages of cellulose (30 and 50 wt%) compared with neat PVA (0 wt%)
Fibers Yield stress (MPa) Tensile modulus (GPa) Strain to failure (%)
0 wt% 65.01 ± 0.57 3.57 ± 0.13 15.45 ± 11.28
30 wt% 58.10 ± 1.08 5.19 ± 0.09 1.49 ± 0.07
50 wt% 51.13 ± 9.46 7.17 ± 0.14 0. 84 ± 0.19
PVA = polyvinyl alcohol.
Fig. 6 - SEM images of the cross-
sec on area of represent ave spec i-
mens aer tensile tests: (A) neat
polyvinyl alcohol (PVA; ×800 magni-
caon); (B) 30 wt% cellulose/PVA
composite (×700 magnicaon); (C)
50 wt% cellulose/PVA composite
(×800 magnicaon); (D) 50 wt%
cellulose/PVA composite (×1.3k
magnicaon). Scale bar: 20 μm.
Fig. 7 - Solubility kinec s of the 50% cellulos e b er/ PVA comp os ite (C 50) un co ated and coated with die re nt per centages of ketone- ald eh yd e
resin (3.3% and 10% resin), with non-water-soluble varnish and with water-soluble varnish: (A) at room temperature and (B) at 45°C.
Conclusions
Once completed, the newly developed material (which
is called Poly-paper) is expected to represent a signicant
step toward the development of highly sustainable packag-
ing, being a very s and strong material that can be shaped
into complex forms and integrated with corrugated board for

Del Curto et al e495
© 2016 The Authors. Published by Wichg Publishing
inclusion in the recycling process of the board itself. Our nd-
ings resulted in the ling of a patent co-owned by the Milan
Polytechnic and NextMaterials srl (12, 13).
Disclosures
Financial support: Bando Congiunto INSTM – Regione Lombardia
2016 - Project IN-RL4 GreenPack.
Conict of interest: None of the authors has any nancial interest
related to this study to disclose.
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