LDPE–wood composites utilizing degraded LDPE as compatibilizer
Introduction
In recent decades, wood–polymer composites (WPCs) have attracted significant attention [1]. WPCs take advantage of the properties of both wood and plastics. To achieve the maximum effect of wood as reinforcing filler, the polymer matrix must be compatible with the wood fibres [2]. The compatibility and the interfacial adhesion can be improved by using compatibilizers or by modifying the wood surface [3]. It is quite clear that a careful selection of the type and level of compatibilizer is needed in order to produce WPCs with acceptable properties and performance [4], [5].
All organic polymers undergo oxidative degradation, and heat and radiation will accelerate this process. Whilst polyethylene (PE) in general is regarded as quite stable, low density polyethylene (LDPE) will undergo thermooxidative degradation (TOD). TOD is often a complex process involving a combination of different mechanisms [6]. The TOD of PE is believed to proceed by a free radical mechanism. This involves, inter alia, the formation of alkyl macro radicals, which in turn react with oxygen to form peroxy radicals. These can further react by abstracting hydrogen from elsewhere on the polymer, forming a hydroperoxide and recreating the macro alkyl radical. The decomposition of the hydroperoxides results in the production of carbonyl and hydroxide groups [7], [8]. Carbonyl groups are often used to monitor the TOD of polyolefins [9], [10]. All of this indicates that the oxidative degradation of PE should create new functional groups that should allow the polymer to be used as a compatibilizer in LDPE–wood composites. The basic function of a compatibilizer is to form an interphase between the wood and the plastic, thus the compatibilizer should have a domain or functionality that is compatible with the wood fibre as well as a domain that is capable of interacting with the plastic matrix [11]. Thus, the idea of degraded LDPE as a compatibilizer for an LDPE–wood composite system is appealing.
Section snippets
Materials
Unstabilized LDPE was supplied in pellet form by Sasol Polymers, Johannesburg, South Africa. It has Mn = 29417 g mol−1, Mw = 142584 g mol−1 and a melting point of 108 °C. The same LDPE was degraded in an oven at 80 °C for 5, 5.5, 7 and 9 weeks to functionalize the LDPE. The formation of functional groups was monitored by FTIR spectroscopy.
Pine wood flour was a cream-white powder supplied by Taurus furniture manufacturers, Phuthaditjhaba, South Africa. It was sieved to <150 μm sizes, and it has a bulk
Results and discussion
Fig. 1 shows the differences between the LDPE spectra before degradation and after 5, 5.5 and 7 weeks degradation. All the spectra show equally intense absorption peaks around 2840 and 2920 cm−1 that correspond to the CH symmetric and asymmetric stretching of methylene groups. Additional peaks are seen in the dLDPE spectra confirming the oxidative degradation of LDPE. The peaks around 1714–1780 and 1000–1100 cm−1 are respectively related to the carbonyl and COC stretching vibrations. The 5 weeks
Conclusions
The objective of this study was to investigate the effect of degraded LDPEs in LDPE/WF composites. The LDPE was degraded at 80 °C for different periods of time and used as compatibilizers in LDPE/WF composites. Part of the investigation was to see which degradation period gave the best balance between functionalization of the polymer and reduced molecular weight. FTIR spectroscopy showed that thermal degradation of LDPE resulted in the formation of several functional groups on the LDPE chains,
Acknowledgements
The National Research Foundation of South Africa and the University of the Free State are acknowledged for financial support of the Project.
References (29)
- et al.
Thermomechanical degradation in the preparation of polyethylene blends
Polym Degrad Stab
(2000) - et al.
Thermal degradation of magnesium hydroxide and red phosphorus flame retarded polyethylene composites
Polym Degrad Stab
(2002) - et al.
Biological degradation of plastics: a comprehensive review
Biotechnol Adv
(2008) Thermooxidative degradation of polyolefins in the solid state: Part 1. Experimental kinetics of functional group formation
Polym Degrad Stab
(1996)- et al.
Mechanical, thermal and microstructure evaluation of HDPE after weathering in Rio de Janeiro City
Polym Degrad Stab
(2003) - et al.
Correlation of physicochemical changes in UV-exposed low density polyethylene films containing various UV stabilizers
Polym Degrad Stab
(1995) - et al.
Durability of HALS-stabilized polyethylene film in a greenhouse environment
Polym Degrad Stab
(1995) - et al.
Thermal and mechanical properties of LLDPE cross-linked with gamma radiation
Polym Degrad Stab
(2001) - et al.
Studies on the photo-oxidative degradation of LDPE films in the presence of oxidised polyethylene
Polym Degrad Stab
(2007) - et al.
The effect of wood extractives on the thermal stability of different wood–LLDPE composites
Thermochim Acta
(2009)
Thermal properties of bio-flour-filled polyolefin composites with different compatibilizing agent type and content
Thermochim Acta
The effect of crosslinking on the properties of polyethylene/wood flour composites
Compos Sci Technol
Mechanical, thermal and morphological characterization of recycled LDPE/corn starch blends
Carbohydr Polym
Thermal, mechanical and electrical properties of copper powder filled low-density and linear low density polyethylene composites
Polym Degrad Stab
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