Functionalization of cellulose through polyurethanization by the additionof polyethylene glycol and diisocyanate

Imam Prabowo1, Fauzia Hanum1, Dick Fereino Firdaus1, Ghiska Ramahdita1,
Mochamad Chalid1,*1

Department Metallurgy and Material Engineering, Faculty of Engineering, Universitas
Indonesia, Kampus Baru UI Depok 16436, Indonesia*Corresponding Author: chalid@metal.ui.ac.id

ABSTRACT
Plastic consumption is becoming one of environmental problems, causing land
pollutions due to plastics’ lack of degradability. This condition leads studies to develop
environmental-friendly materials, one of them innovation on cellulose addition to plasticproducts. Cellulose, the largest main component of natural fibers, is known for its
biodegradability and availability on earth, which also performs high strength andspecific modulus to enhance polymeric materials properties. On the other side,different nature of cellulose which is non-polar and polyurethane which is polar causing
poor compatibility between them. This research was focused to enhance thecompatibility through interface reaction, also known as grafting technique, between
isocyanate and cellulose, and investigate the effects of diisocyanate and cellulose ratioon the properties of hybrid polyurethane-cellulose material. Investigation of theexperiment results was conducted by using Fourier-Transform Infrared (FT-IR) toconfirm the functional groups, Simultaneous Thermal Analysis (STA) to investigate
thermal stability, Scanning Electron Microscope (SEM) to examine the surface
morphology and 1H-Nuclear Magnetic Resonance (1H-NMR) to probe the structure ofhybrid material. The results has revealed that the structure of hybrid material consistsof cellulose as chain extender in hard segment which connect two diisocyanate
compounds and polyol as soft segment. Furthermore, the addition of cellulose could
enhance thermal stability, whereas the addition of diisocyanate could decrease it.

Keywords: cellulose, chain extender, polyurethane, thermal stability, grafting
technique

1. INTRODUCTION

Over the last century, plastics are already known as a major commodity which
are widely used in various applications including military, construction, packaging,household devices and automotive parts. The plastic products are commonly madefrom petro-polymer due to low cost, low density, and easiness to process. Moreover,petro-polymer has better mechanical properties compared to metals and ceramics,

and addition of fibers, usually carbon and glass fiber, offers higher strength and higher
modulus elasticity [1].
Polyurethane is one of plastics which has great versatility and variety ofapplications and functions, relying on the precursors chosen in the formulation [2]. It
commonly can be obtained from the reaction between diisocyanate compounds andpolyols or diols. A number of reactions resulting in polyurethane from biomass-based
monomers have been reported recently [2-6]. These reactions involve synthesis ofbiomass polyurethane comprising of several stages namely pre-polymerization
followed by chain extension. In addition, direct polymerization to create high molecularweight of polyurethane was also reported by reacting with a relatively high molecularweight monomers [3]. The structure of polyurethane itself typically is constructed by analternating phase called soft segment (SS) and hard segment (HS). The ratio between
HS and SS primarily determines the entire properties of polyurethane that HS isresponsible for the mechanical and high thermal properties, while SS is responsible forelastic and low thermal properties. So that the properties of polyurethane can bevaried by manipulating the amount of HS and SS [4-7].
Besides, usage of carbon and glass fibers in polymer products has emerged
problems of land pollution and started to be an important concern. As a result, inseveral decades the use of natural fiber has replaced those inorganic materials insome applications due to the ability such as degradation and decomposition [8-16].
The most important content that are extracted from natural fibers is cellulose which
possess high strength and excellent specific modulus. In particular, several scientists
have carried out the experiments involving grating technique of cellulose topolyurethane to get hybrid-polyurethane materials, for instance Belgacem et al [17]who have combined pre-formed of PCL and phenyl isocyanate with cellulose as achain extender and followed by Samain et al [18] who have conducted grafting
technique of isocyanate to microcrystalline cellulose with PLA and PHA polymer.
According to the aforementioned explanations, this research was performed to
study the structure of hybrid polyurethane-cellulose material and to investigate theeffect of cellulose to the thermal stability. The experimental results were evaluated by
1

H-NMR to analyse the structure, FTIR to characterize chemical content, STA is toanalyze physical changes such as the glass transition temperature (Tg) and melting
temperature (Tm) and thermal stability and SEM to observe the morphological surface
within hybrid polyurethane-cellulose material.

2. EXPERIMENTAL SECTION
2.1

Materials
The polyurethane firstly was synthesized by pre-polymerization mechanism

involving reaction between 15 grams of polyethylene glycol (PEG) Mw: 6000 g/mole as
the SS and two moles of 4,4′-methylenebis (Cyclohexyl isocyanate) (HMDI) as the HS.
The reaction was accelerated by adding two drops of dibutyltin dilaurate (DD) as acatalyst and the addition of cellulose with the composition ranging from 0.5 gram to 2.5grams. All materials were obtained from Sigma-Aldrich, inc.
2.2

Instrumentation

2.2.1

1

H-Nuclear Magnetic Resonance (1H-NMR)

1

H-NMR measurement was carried out to analyse the structure of hybrid

polyurethane-cellulose material. Characterization procedure was conducted at DTMMFTUI using NMR Jeol 500MHz. Measurement conditions are 23⁰C for the temperatureand 6 Pa for the pressure (vacuum).

2.2.2

Fourier Transmission Infra-Red (FT-IR)
FT-IR spectra were recorded by using a Perkin-Elmer FTIR spectrometer. It

was carried out to obtain an infrared spectrum of absorption of a solid, liquid or gas
and to collect the resolution of high spectra on a widely range spectra data. It is utilized
to further analyze the structure of material. Each sample recording comprising 30
scans recorded from 400 to 4000 cm-1.
2.2.3

Simultaneous Thermal Analysis (STA)
STA measurements were recorded by using a Perkin-Elmer 6000. It has rangeof temperature from 15 to 1000 °C and was carried out to analyze physical changes
such as glass transition temperature (Tg) and melting temperature (Tm) and thermalstability. This technique conducts the experiment on which the material and reference
are heated and chilled on certain condition.
2.2.4

Scanning Electron Microscope (SEM)
Surface morphology of polypropylene composite was observed by using Field

Emission Scanning Electron Microscope FEI Inspect F50 to image the morphology
with accelerating voltage of 30 kV, resolution and magnification are 1 nm and 500.000

times respectively. More specifically it was used to clearly investigate the compatibility
between cellulose and polyurethane.
2.3.

ProcedurePreparations of hybrid polyurethane-cellulose material consist of two steps

namely pre-polymerization mechanism and grafting mechanism. Firstly, the prepolymerization process began with filling Dimetilformamida (DMF) as a solvent and 15grams of Polyethylene glycol 6000 into a schlenk tube. Then, the schlenk tube washeated to 80°C and stirred up for one hour. Before that it was fluxed with nitrogen gas
to ensure that there is no moisture trapped in the schlenk tube. After one hour, twomoles of HMDI was injected into the schlenk tube and followed by two drops of DD tospeed up the pre-polymerization reaction. Then, the pre-polyurethane was obtained
after mixing all of components stirred for one hour and heated to 80°C. Secondly, after
the pre-polyurethane was formed, the grafting mechanism was carried out to get thehybrid polyurethane-cellulose material. The pre-polyurethane material formed wasindicated as white viscous liquid. Then, grafting mechanism was started filling aschlenk tube with cellulose as a chain extender with the temperature raised to 80°Cand stirred up to one hour. Finally, the reaction was terminated by using 20 ml of water
and waited for up to one day until occurred a phase separation in which the hybrid
polyurethane-cellulose precipitated in the bottom of glass vessel and water, DMF andDD were floated on the surface.

3. RESULTS AND DISCUSSION
3.1 The structure of hybrid polyurethane-cellulose material
The pre-polymerization reaction occurred when diisocyanate attack hydroxyl
group in the polyols or diols compounds to form urethane group which typically hints a
polyurethane polymer [18]. After the pre-polymerization process, the remaining
diisocyanate compound (–N=C=O) reacted with the hydroxyl group of cellulose
through grafting mechanism in which diisocyanate has a role as coupling agent whichforms chemical or physical bonding between interface of cellulose and polyurethane. It
also can increase the compatibility of hybrid polyurethane-cellulose material [19]. The
result of the entire polymerization process is a hybrid material between cellulose andpolyurethane.

Figure 1. The scheme of formation of hybrid polyurethane-cellulose material.
According to the NMR result, the urethane C=O group and amide group formed in thehybrid structure. The formers depicted at from 0.86 to 1.07 ppm, while the spectrum at
8.22 ppm is for the NH with C=O group and at 3.75 ppm is for the NH and C group.

Figure 2. The H-NMR result of hybrid polyurethane-cellulose material.

In order to further depict the structure of hybrid material, FTIR spectra isneeded to clearly show the spectra emerged in the hybrid material’s structure.

Figure 3. FTIR Spectra of hybrid polyurethane-cellulose material. A) 2.5 grams, B) 1.5grams, and C) 0.5 gram of cellulose
According to the FTIR spectra, a number of spectra emerge from the graph including
amine bonds from 1280 – 1342 cm-1 , secondary amine at 2887 cm-1, C-O acyl bond at
1242 cm-1, urethane at 1703 cm-1 and amide group at 1553 cm-1 . Secondary amine
itself indicate that the diisocyanate compound has reacted and created the urethanegroup with hydrogen atoms. In addition, the addition of cellulose fibers showed on thedepth of peaks at 1104 cm-1 and 3361 cm-1.
3.2 The thermal stability of hybrid polyurethane-cellulose material.
The hybrid polyurethane-cellulose material shows thermal characteristics
related to the amount of SS and HS. Furthermore, melting and glass transition
temperature rely on the addition of cellulose as the addition of cellulose itself affects
the amount of HS contributing as a chain extender in the hybrid polyurethane-cellulosematerial. Cellulose which has intra and inter hydrogen bondings then interacted withhydrogen bonding of diisocyanate group in the HS to form cross linking [20,21]

subsequently increasing the temperature of hybrid polyurethane-cellulose material.
The greater amount of cellulose added to the hybrid material has definitely increased
the temperatures caused by an increase of the interaction of hydrogen bonding.
450

420.1

415.8

411.5

400
350
300
250
200

100

145.6

105.3

150

59.1

500A

Tg

B

Tm

CFigure 4. Thermal characteristics of hybrid polyurethane-cellulose material: A) 2.5grams, B) 1.5 grams, and C) 0.5 gram of cellulose
The addition of cellulose has raised the thermal stability of hybrid polyurethanecellulose material since it has role to form cross linking in the HS through hydrogenbonding mechanism and as a result, the proportion of hard segment increased thethermal stability of the material [22].

Figure 5. Thermal stability of hybrid polyurethane-cellulose material: A) 2.5 grams andC) 0.5 gram of cellulose

3.3 Morphological surface of hybrid polyurethane-cellulose material.
The morphological surface has a relationship with the thermal properties. The
good dispersion and distribution of cellulose are responsible to form the hydrogenbonding between urethane groups and hydroxyl group of cellulose [23]. Furthermore,they affects the formation of cross linking region which contributes to stabilize thehybrid material thermally as well.

Figure 6. Morphological surface of hybrid polyurethane-cellulose material left (C) andright (A)According to the graph, the left image (C) shows that the cellulose (white dots)
disperses and distributes on the whole surface of hybrid material, while the right image(A) has the little white dots on its surface. It indicates that the greater amount ofcellulose in the hybrid material affects the percentage of formation of cross linking
which formed by hydrogen bonding between urethane groups and hydroxyl group ofcellulose. In other words, the greater amount of cellulose has produced a good
distribution and dispersion on the surface of material. As a result, it is thermally stable
and has increased the thermal characteristics of hybrid polyurethane-cellulose material.
4. CONCLUSIONSThe structure of hybrid polyurethane-cellulose material consists of cellulose as achain extender and diisocyanate compound in the HS region and Polyethylene glycol
6000 as a SS region. The addition of cellulose increases both glass transition andmelting temperature, thus enhances the thermal stability. Morphological surface showsthat the addition of cellulose also affects the thermal properties of hybrid material due
to good distribution and dispersion on the surface of material.
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