Characterization and reprocessing of greenhouse films

doi:10.1016/S0141-3910(01)00008-8

Polymer Degradation and Stability

Volume 72, Issue 1, 2001, Pages 141-146

https://doi.org/10.1016/S0141-3910(01)00008-8 Get rights and content

Abstract

Films for greenhouses are an attractive source of post-consumer plastic materials because they are mainly made of polyethylene and can be easily collected in large amounts in small zones. The types of polymers for this application are, however, increasing and the films contain not only additives and stabilisers, but also fertiliser and pesticide residues. Finally, the extent of photooxidative degradation undergone during the use can strongly influence the recycling operations and the final properties of the secondary material. In this work, a complete characterisation of post-consumer films for greenhouses has been carried out and the properties of the recycled material have been correlated with the number of reprocessing steps and compared with those obtained by reprocessing virgin scraps of the same composition. The presence of small amounts of low molecular weight compounds (photooxidized species and pesticide residues) does not compromise the use of the recycled plastic in many applications. The mechanical properties decrease with the number of reprocessing steps and with increasing level of photooxidative degradation but are good enough for many applications.

Introduction

The amount of plastic materials used in agriculture is continuously increasing. Plastic materials are used for greenhouse covers, mulching, piping, packaging and other applications. Films used for greenhouses can be considered as an easy source of materials for recycling. Indeed, large amounts of film can be easily collected and because of the homogeneity of the polymers used for this application, the recycling operations can be relatively easy. The secondary materials are usually employed for the production of blown film for packaging.

However, the polymer materials used for these films are changing and, in particular, the use of blends is continuously increasing like the use of additives. These additives are used in relatively large amounts for different aims, like photooxidation resistance, antifog, etc. Moreover, the films can absorb fertilisers and pesticides that can compromise the use of secondary materials coming from greenhouse cover films in many applications. The UV exposure gives rise to major modification of the macromolecular chains with chain breaking, formation of oxygenated groups, possible formation of branching and crosslinking and so on [1], [2], [3], [4]. Finally, the reprocessing operations can induce further degradation due to the thermomechanical treatment in the melt [5], [6], [7], [8].

When post-consumer polymers are treated by repetitive processes, it is then necessary to determine the relationships between the actual structure and morphology, resulting because of the degradation undergone during the lifetime, the reprocessing conditions and the properties of the secondary materials.

In this work post consumer films coming from greenhouse cover films were characterised to evaluate polymers, additives and the possible presence of pesticides residues and were reprocessed by repetitive extrusions in order to evaluate rheological and mechanical properties to be correlated with the number of processing steps and with the initial structure.

Section snippets

Experimental

Greenhouse films have been collected in the province of Ragusa (Sicily, Italy where the most important production of covered cultivation is located). LDPE, LLDPE and EVA copolymer are the most commonly used polymers for the production of films. The collected films had been used and exposed to sunlight for about 1 year. Post-consumer films (PF) were washed, dried and cut to pieces by an industrial apparatus. For a valid comparison, virgin films (VF) of the same average composition, coming from

Results and discussion

The average composition of the material for recycling, obtained by GC–MS analysis, calorimetry and IR spectroscopy is shown in Table 1.

The chromatograms of post-consumer film extracts show many signals. Many of them were identified as linear hydrocarbons with different chain length (C₁₂–C₃₀). Uncertainty exists on attribution of some low intensity signals that, however, can possibly be ascribed to fertilisers or pesticides residues. On the other hand, the presence of octabenzone

Conclusions

The recycling of post-consumer films for greenhouses is strongly dependent on the initial structure of the plastic materials and on the processing conditions. The films contain small amounts of low molecular weight compounds probably coming from the photooxidation of the PE molecules and from the absorption of fertiliser and pesticide residues.

The amount of these compounds is, however, small and does not prevent the use of the recycled materials in many applications.

The properties of the

Acknowledgments

This work has been financially supported by MURST, Programma di Ricerca di Interesse Nazionale, 1998. N.T.D. express thanks for the financial support of INCA (Interuniversity Consortium Chemistry for the Environment), Venice (Italy).

References (8)

F.P. La Mantia
Radiat. Phys. Chem.
(1984)
A. Tidjani et al.
J. Appl. Polym. Sci.
(1993)
M. Sebaa et al.
J. Appl. Polym. Sci.
(1993)
L. Angùlo et al.
J. Appl. Polym. Sci.
(1994)

There are more references available in the full text version of this article.

Cited by (36)

Properties and printability of compression moulded recycled polyethylene
2014, Materials and Design
The goal of the research was the determination of the properties and printability of polymeric materials made from the recycled polymers, low-density polyethylene (LDPE) and high-density polyethylene (HDPE). From the primary (virgin) polymers and secondary (recycled) polymers that were obtained from the separately collected fractions of waste packaging, compression moulded plates were produced. The tensile properties of 1 mm and 2 mm thin plates were correlated with some structural characteristics: melting point, melting enthalpy and crystallinity degree. It was determined that the recycling process changes the melting behaviour, lowers the crystallinity and to some extent influences the tensile properties of plates. LDPE and HDPE compression moulded plates were printed with the UV inks on the large format digital UV inkjet printer Océ Arizona. To investigate the printability of plates made from the recycled materials some of their surface properties were determined. Higher optical density, area of ink coverage and dot gain of the printed HDPE plates compared to the LDPE plates are the consequence of higher roughness, higher surface energy with prevailing part of the polar component. By adding 4% of coloured master batch to the recycled polymer at moulding, the uniformity of colour is improved leading to the higher print quality. The results have shown that the digital UV inkjet printing technique could be applied for printing recycled polyethylene plastic materials, used for disposable low cost packaging products.
Experimental tests and technical characteristics of regenerated films from agricultural plastics
2012, Polymer Degradation and Stability
Citation Excerpt :
All materials in this group, if compared to F1 and F2, do not have aluminium, sulfur, magnesium, cuprum, technetium, cadmium and calcium and potassium feldspar. Tzankova Dintcheva et al. [26], when comparing the results of the chemical analysis and of the mechanical tests on specimens of recycled films with those obtained in the virgin material, concluded that the recycled material can be used again in a lot of applications even if its optical characteristics decrease with the number of the extrusive passages, especially due to oxidative degradation. Mechanical characteristics, instead, even worse than the virgin material, remain relatively good after a lot of extrusions.
Current agricultural practices require the use of large quantities of plastics, which contribute to a significant increase of the quantity and quality of agricultural production, but also require high quantities of plastic waste to be disposed in such way that will not have a negative effect on the landscape and the agro-ecosystem. In this paper the results of an experimental investigation of the possibilities of producing new regenerated plastic films through mechanical recycling, from post-consume agricultural plastic films are analysed. Six recycled films, made from agricultural low tunnel and greenhouse covering films as well as from HDPE bags for agrochemical packaging, have been extruded producing films of different thickness. These regenerated films were characterized by means of mechanical and spectrometric tests and SEM + EDS analysis. The obtained results show that without adding any additives into the blends good mechanical and spectral properties can be achieved by mixing the greenhouse and low tunnel recycled plastic film coverings.
Analysis of photo-chemical degradation behaviour of polyethylene mulching film with pro-oxidants
2011, Polymer Degradation and Stability
It is generally accepted that polyolefins are bioinert. The last years, a new class of photodegradable polyethylene films with pro-oxidants has been developed, exhibiting optimised operational properties in terms of controlled UV and/or thermal ageing leading to an abrupt, predefined to some extent, rapid fragmentation into very small fragments. These photodegradable or fragmentable polyethylene films are promoted in the market for various commercial applications. In some cases, these materials are presented as, or are claimed to be, biodegradable materials. Such materials are already used in agriculture in the form of photodegradable mulching films which become fragmented into small remains after the end of their useful lifetime and are incorporated into the soil. However, it has not been verified yet beyond any doubt, that these remains do in fact biodegrade in natural soil, under what conditions, at which rate and what are their effects in agricultural production, the soil and the environment. An experimental investigation has been carried out focusing on the combined effects of critical factors on the controlled (predefined) photo-chemical degradation of photodegradable mulching LLDPE films with pro-oxidants and the behaviour of their remains in the soil. The analysis of the photo-chemical degradation behaviour presented in this paper was carried out through parallel experiments performed under real field and controlled laboratory conditions. The main factors investigated include materials, exposure time, temperature and UV radiation.
Study of the degradation mechanisms of polyethylene during reprocessing
2011, Polymer Degradation and Stability
The present work aims at evaluating the behaviour of various grades of high and low density polyethylene subjected to continuous injection moulding operations. It is based on a wide range of experimental techniques that allowed the establishment of relationships between the observed property changes and the structural modifications developed in the polymers. The study confirmed the coexistence of two distinct degradation mechanisms, crosslinking and chain scission, that occur due to thermo-oxidative reactions arising during the different injection moulding stages. The relative importance of these two mechanisms depends on the material structure and on the processing conditions used. It was also possible to confirm that the polyethylenes with lower molecular mass show low sensitivity to degradation during reprocessing. Furthermore, the more branched polymers (as is the case of LDPE) also proved to be less sensitive to thermo-degradation phenomena. Overall, it was concluded that the primary recycling of polyethylene, if performed under well controlled conditions, will lead to only minor material property losses.
Closed-loop recycling. A case study of films for greenhouses
2010, Polymer Degradation and Stability
Citation Excerpt :
During this step, the thermomechanical stress acting on the melt can further increase the level of degradation of the post-consumer material. The flow curves of PF and of the virgin LDPE extruded 1 and 5 times are reported in Fig. 2 [1]. The viscosity of the PF samples at low shear rates is higher than that of the virgin samples because of the presence of branched or perhaps cross-linked structures formed by photo-oxidative degradation during the lifetime.
The degradation undergone by plastic films used for greenhouse coverage is the main cause of the worsening of the processability, of the mechanical properties and of the durability of secondary materials obtained by their recycling. This means that this secondary material cannot be processed to produce films for the same applications (closed-loop recycling).
In this work different strategies are proposed to improve the processability, some mechanical properties and the resistance to photo-oxidation of these secondary materials. In particular, homopolymer blends or multilayer films where the secondary material is used in combination with virgin polymer give the best results.
Recycling and disposal of flame retarded materials
2008, Advances in Fire Retardant Materials
Legislations, coupled with an increasing environmental sensitivity, have enhanced the interest in plastic recycling with the intent of reducing the waste stream. This chapter provides the state of the art of flame retardancy of polymeric materials, the approaches and technologies available for plastic recycling as well as the related legislations and European Directives. The chapter then analyses how the presence of flame retardants affects recycling of the plastic waste stream.

View all citing articles on Scopus

View full text

Characterization and reprocessing of greenhouse films

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgments

Radiat. Phys. Chem.

J. Appl. Polym. Sci.

J. Appl. Polym. Sci.

J. Appl. Polym. Sci.