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  • 1.
    Espert, Ana
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Strategies for improving mechanical properties of polypropylene/cellulose composites2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The interest for polypropylene/cellulose composites has experienced a great increase in different applications such as car interiors and construction materials. Cellulose fibres are inexpensive, renewable, biodegradable, they present lower density and their mechanical properties can be compared to those of inorganic fillers. However, several factors must be considered when designing polypropylene/cellulose composites: the poor compatibility between the hydrophilic fibres and the hydrophobic thermoplastic matrix leads to a weak interface, which has to be improved by coupling agents; the hydrophilic nature of the fibres makes them very sensitive towards water absorption, which also leads to a loss of properties and swelling with subsequent dimensional instability; the reduced thermal stability of cellulose fibres leads to degradation of the fibres at thermoplastic processing temperatures producing odours in the final material; and finally the properties of composites are greatly influenced by the structure, size and quality of the fibres.

    Pulp fibres modified by different methods in order to enhance the compatibility fibre-matrix, were tested. Modified fibres led to improved mechanical properties and thermal behaviour when used in composites with recycled polypropylene.

    Four different types of natural fibres were used as reinforcement in two different polypropylene types: virgin and recycled polypropylene. The mechanical properties of the composites were mostly dependent on the fibre loading and slightly dependent on the type of fibre. Moreover, water absorption kinetics was studied by the Fickian diffusion theory. After absorption, a remarkable loss of properties was observed.

    Hydrolysed cellulose fibres showed a greater enhancing effect on polypropylene than non-hydrolysed cellulose fibres. This is attributed to the greater mechanical properties of reduced cellulose structures.

    The effect of using cellulose fibres in PP/clay nanocomposites was also studied. The interaction between the clay particles and the cellulose fibres and the combined effect of both reinforcements were believed to be the main reasons for the enhancing properties.

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  • 2.
    Espert, Ana
    et al.
    KTH, Superseded Departments, Polymer Technology.
    Camacho, Walker
    KTH, Superseded Departments, Polymer Technology.
    Karlsson, Sigbritt
    KTH, Superseded Departments, Polymer Technology.
    Thermal and thermomechanical properties of biocomposites made from modified recycled cellulose and recycled polypropylene2003In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 89, no 9, p. 2353-2360Article in journal (Refereed)
    Abstract [en]

    Residual cellulose fibers from the paper industry have been used as reinforcements in recycled polypropylene (PP) composites. The main obstacle to obtaining good properties with this biocomposite is deficiencies in the compatibility between the nonpolar matrices and the polar cellulose fibers used as reinforcements. The aim of this work was to improve the compatibilization between these cellulose fibers and the PP matrix with four different methods: modification by the addition of polypropylene-maleic anhydride copolymer (PPgMA) during the process of blending, preblending modification of the cellulose with a solution of PPgMA, modification of cellulose by silanes (vinyltrimethoxysilane), and acetylation of cellulose. Blends with all of the differently modified celluloses were prepared with the cellulose content varied up to 40%, and then all of the blends were subjected to thermal (differential scanning calorimetry and thermogravimetric analysis) and thermomechanical (dynamic mechanical thermal analysis) analyses. The results showed that the addition of cellulose fibers improved the thermomechanical behavior of the PP, increasing the value of the log of the dynamic modulus, and affected the thermal and thermooxidative behavior. Moreover, an advantage of the use of a recycled PP containing a small quantity of ethyl vinyl acetate (EVA) as a prime material in the composition was the enhancement of mechanical properties. The use of these methods for the modification of cellulose led to more desirable thermal and thermooxidative stabilities.

  • 3.
    Espert, Ana
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    de las Heras, Luis A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Emission of possible odourous low molecular weight compounds in recycled biofibre/polypropylene composites monitored by head-space SPME-GC-MS2005In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 90, no 3, p. 555-562Article in journal (Refereed)
    Abstract [en]

    A disadvantage of the use of natural fibres to reinforce polypropylene is their poor thermal stability, which results in their degradation at processing temperatures of the composites. As a result of this, there is a formation of low molecular weight compounds that are responsible for undesirable odours. Head-space-solid phase microextraction (HS-SPME) was used as a sample preparation technique and gas chromatography-mass spectrometry (GC-MS) was used to identify the low molecular weight compounds in natural polypropylene/polypropylene composites after simulating degradation. Among the compounds found in the samples, there are fragments of PP chains as heptadecane, compounds from antioxidants such as 2,4-bis(1,1-dimethylethyl)-phenol, and p-tert-butylphenol, and compounds from biofibres ageing, such as ethylparaben and vanillin. Numerous carboxylic acids were also identified, being these most probably the source of the undesirable odours.

  • 4.
    Espert, Ana
    et al.
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Karlsson, Sigbritt
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Novel PP/Montmorillonite/cellulose hybrid composites: study of the interaction between Montmorillonite clay and celluloseManuscript (preprint) (Other academic)
  • 5.
    Espert, Ana
    et al.
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Vilaplana, Francisco
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Karlsson, Sigbritt
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Comparison of water absorption in natural cellulosic fibres from wood and one-year crops in polypropylene composites and its influence on their mechanical properties2004In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 35, no 11, p. 1267-1276Article in journal (Refereed)
    Abstract [en]

    Environmentally beneficial composites can be made by replacing glass fibres with various types of cellulose fibres. Fibres from pine or eucalyptus wood and also one-year crops such as coir, sisal, etc. are all good candidates. The poor resistance towards water absorption is one of the drawbacks of natural fibres/polypropylene composites. New natural fibres/polypropylene composites were made and the water absorption in them was studied by immersion of the composites in water at three different temperatures, 23, 50 and 70 degreesC. The process of absorption of water was found to follow the kinetics and mechanisms described by Fick's theory. In addition, the diffusivity coefficient was dependent on the temperature as estimated by means of Arrhenius law. A decrease in tensile properties of the composites was demonstrated, showing a great loss in mechanical properties of the water-saturated samples compared to the dry samples. The morphology change was monitored by scanning electron microscopy studies of the samples before and after exposure to water and the devastating effect of water on the fibre structure was shown.

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