FAIR-CT95-0195 AFPP-QCPC: Annual fibre reinforced polypropylene composites for industrial applications: development of a quality controlled fibre production chain

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	Proposal No:	FAIR-CT95-0195
	Date Prepared:	July 2001, September 1999, March 1998
	Source:	Final Report Executive Summary Second Annual Progress Report First Annual Report Summary

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Final Report Executive Summary

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Second Annual Progress Report

Summary

Objectives

This project has three principal objectives:

• the stimulation of the industrial use of annual fibre crops which can be grown in EU-countries, especially indigenous crops like flax and hemp
• the development and optimisation of (pre)treatment and processing methods for annual fibres to specifically adapt them to function as re-inforcers in composites with the synthetic thermoplastic polypropylene (PP)
• the development of a composite material composed of polypropylene, isotropically reinforced by randomly oriented annual fibres (AFPP) and use of such material in industrial applications particularly automotive components

Activities The central theme of this project is the use of maleic anhydride (MA) as compatibiliser between PP and the lignocellulosic fibres. The project has adopted an integrated approach covering the complete production chain of AFPP, including fibre production, fibre opening, fibre treatment, matrix treatment, compounding process and production of actual prototype parts from composite materials. The most important issues for the purpose of the production of AFPP-based parts with favourable properties include the optimisation of fibres' physical and chemical characteristics by the fibre opening (pulping) process, and the development of treatments to modify the composition of the individual fibres more radically.

The introduction of new components in/on the fibres is being developed using two different types of treatment. The first makes use of water borne components, offering the possibility of relatively easy integration with the aforementioned opening process. The second type of treatment is based on the use of organic solvents that are more likely to produce a more profound composition change as well as to enable a greater number of alternatives:

• adaptation of the PP to increase its suitability as a matrix
• development of an efficient compounding process and in conjunction development of feeder technology applicable to dry (pre-treated) annual fibres
• optimisation of end-product manufacturing techniques to fully exploit the properties of AFPP

Criteria of major importance, other than the material properties, are the environmental impact (investigated in particular as part of a Life Cycle Analysis) and costs of the individual process steps as well as the integrated processing chain.

To carry out the project, a three-year work programme was defined involving a number of specific tasks, as detailed in the next section.

Results and discussion

Task I: Fibre opening research Objectives are as follows:

• selection of suitable fibre varieties
• optimisation of the fibres morphological characteristics
• sub-optimisation of the fibres' chemical characteristics (additional optimisation: see task 2)
• Establishing the importance of paper related parameters

Objective 1 resulted in a selection of three flax and three hemp raw fibre qualities, based on general availability in the market. These raw fibres were opened by two chemical processes with two additional variations as well as two (chemi)mechanical processes, again with two additional variations. From these six raw fibre qualities and 48 pulps a selection was made to narrow down the number of fibres and pulps. The flax and hemp grades Lincell B (bleached and unbleached) and Hempcell B (bleached and unbleached) were selected together with their raw fibres (20% straw for the flax fibre and 40% straw for the hemp fibre) together with the extruder pulps of the raw fibres. Objective 2 and 3 resulted in both morphological and chemical optimised characteristics resulting in the following phenomena:

• a positive correlation with decreasing straw content
• similar trends of bleached pulps with respect to the unbleached ones with a slight reduction of the absolute values after the bleaching sequence
• similar trends of refiner pulps with respect to the extruder ones with a slight reduction of the absolute values after the refining technique
• no significant processing differences between the flax and hemp varieties

Results from objective 4 showed that fibre dispersion inside the plastic matrix were not as good as expected due to the inherent characteristics of these pulps after processing. In order to solve the problem, the use of a hammer-mill (to fluff the pulp) was investigated. Although this procedure appeared acceptable in lab-scale experiments, for industrial scaling up the following disadvantages were identified:

• high volume equipment required for an appropriate processing,. This represents a high initial investment
• noisy working
• very low density of the resulted fluff fibres, implying a difficult extrusion feeding system and an irregular control
• reduction of the final fibre length and formation of an important quantity of "dust" or powdered pulp

Considering the fact that the fibre dispersion inside the plastic matrix is directly related to the inherent characteristics of fibres and the interaction between them, the effect of different chemical products (so called 'debonding agents') which can be used to reduce the tensile properties between the fibres was also investigated.

Task 2: Fibre composition modification research The general objective of this task is modification of the chemical composition of the fibre surface to improve the fibre-matrix interaction. Originally it consisted of two sub-tasks which were to focus on the modification through physically (task 2.1) and chemically (task 2.2) components, respectively. However, these objectives were modified, in part due to the fact that aqueous emulsions of gMA-PP have become commercially available. Hence, it was decided to refocus the subdivision of tasks 2.1 and 2.2 as composition modification in aqueous and organic media, respectively, with the organic solvent reactions carried out to achieve derivatisation,

Under the revised objectives, task 2.1 investigated aqueous medium based introduction of new components. This included gMA-PP derivatisation of the fibres' surface, using water borne emulsions (both cationically and anionically stabilised), with evaluation of the modifying activity. The cationically stabilised gMA-PP emulsions appeared a better choice for the modification of natural fibres than anionically stabilised ones. Although a seemingly good procedure for treating fibres with gMA-PP emulsions was developed, the compounded materials in which the derivatised fibres were used did not show any significant improvement relative to the materials in which untreated fibres were used.

In task 2.2, in which organic solvent based introduction of new components was investigated, maleinyl derivatisation of the fibre surface was carried out as specifically as possible, with attention paid to the following aspects:

Processing parameters that could affect the maleic load on the fibres were studied. These parameters included reaction time, maleic anhydride concentration, fibre pre-drying, the use of triethylamine and the reaction time. Alternative methodologies employing other organic solvents, or smaller volumes of organic solvent. Tested variables included:

• the use of an alternative, lower boiling temperature solvent
• the use of smaller volumes of an appropriate solvent for reaction
• the use of water as a reaction solvent
• sublimation of MA on the fibre (no solvent method)

One of the main promising conclusions drawn from the results of these experiments is the that modification of fibres with an appropriate MA derivatisation content is possible on lab-scale without the use of organic solvents, reducing the waste stream.

Task 3: Matrix research This task had two main objectives; to develop optimal fluidity of the matrix to achieve wetting of the fibres and to develop optimal matrix blend with gMA-PP to achieve optimal chemical bonding between matrix and fibres. While studying gMA-PP, it became apparent that a more accurate method, than those available either in the public domain or proprietary, was required to establish the exact composition of gMA-PP. For rapid measurements, an FTIR-method for the quantitative determination of the maleic anhydride content was developed. The method appeared to be reliable and accurate. Solvay used the FTIR-method for the determination of the maleic anhydride content of the gMA-PP grades they produced. These grades cover a broad spectrum of parameters including MA concentration, molecular weight and crystallinity. So far, after compounding experiments with these gMA-PP grades as a part of task 4, the most important parameters seemed to be the molecular weight and the crystallinity.

Task 4: Compounding process research This task had three main objectives:

• definition of the optimal processing conditions in general
• development of a practically usable fibre feeding system
• development of conditions to graft maleinyl derivatised fibres onto the matrix

The screening of all of the raw fibre and pulp grades, in terms of their respective influence on the mechanical properties of the resultant polypropylene composites, has been completed. The picture emerging from the kneader-derived data can be generalised as follows:

• fibre opening before compounding positively affected the resulting composites
• chemimechanical pulps produced considerable strength improvement, although the improvement with chemical pulps was even better
• extruder mechanical pulps showed better results than the refiner pulps
• unbleached chemical pulps resulted in more strength improvement than their bleached counterparts and, on average low chemical usage produced better results than high chemical use
• the shift/bastfibre ratio correlated negatively with the mechanical properties improvement of the composites

Based on these results, fibres and pulps were selected for further experiments:

• raw flax fibre containing 20ww% of shives
• raw hemp fibre containing 40 ww% of shives
• high chemical/bleached pulps (CELESA grades B Lincell B and B Hempcell B) and their unbleached counterparts (U. Lincell B and U. Hempcell B)
• extrusion grades produced under fibre condition (CF20 EF and CH40 EF)

Several gMA-PP grades varying in molecular weight, maleic anhydride concentration and crystallinity were tested. The results obtained with the different modifiers showed some general trends:

• the flexural, strength, flexural elongation and Charpy impact strength increased upon addition of the modifier, whereas the flexural modulus was hardly affected
• the differences in flexural strength as found after compounding with raw fibres and distinct opened fibres, without a modifier added, vanished after compounding with a gMA-PP grade, whereas the differences in Charpy impact strength appeared to become more pronounced
• the increase in mechanical properties correlated positively with the concentration of the modifier - an optimum or levelling-off effect was noticed after addition of 0.009% maleic anhydride
• from all the tested gMA-PP, grade GPOO12 appeared the type with the highest increase in mechanical properties - this has a low MA concentration but a high molecular weight and a high crystallinity

The influence of ageing resistance on the flax fibre / pulp composites was investigated. Three different fibres (B.Lincell B, U.Lincell B and CF20) were compounded and tested using two different ageing resistance norms: PSA Norm D47-1309 and an ageing test developed at ECIA. From the results the following conclusions were drawn:

• it appeared that the ECIA test gave a more reliable ageing resistance evaluation than the PSA norm
• the highest mechanical properties, even after the ageing resistance test, were obtained with the unbleached (U.Lincell B) composite materials
• the mechanical properties meet the requirements of the product profile

The development of a practically usable fibre feeding system continued at pilot scale and on industrial scale.

Task 5: End-product manufacturing The first objective of this task is the development of the technology required to manufacture end-products from AFPP. Taking into account the recognised mechanical properties of cellulosic fibres/PP compounds as well as their environmental limits (ageing and thermal sensitivities), the annual fibres / PP composites are well suited to the development of automotive interior parts. A car part prototype chosen was chosen, in the form of a door panel trim. The specific tooling was developed and carried out during 1997. For the production of the prototype in an integrated production chain it appeared necessary to develop a reliable and reproducible cellulosic fibres feeding device.

First, attention was paid to pulp defibrillation, the so-called fluffing process for which a hammer mill device was used. It appeared that although a good composite homogeneity was obtained after compounding, the fluffing technology was clearly incompatible with the convenient extruder feeding devices. Moreover, the fluffing process was responsible for fibre length reduction that correlated negatively with the impact strength of the resulting composites. Therefore experiments were performed with small pulp pellets produced with a paper mill device. These pellets were successfully fed into the extruder with a convenient extruder feeding device. However, the resulted compound after feeding of B.Lincell B pellets presented a heterogeneous composition. Following these experiments, it appeared that the concept of extruder feeding from pulp pellets is an attractive option, but requires adaptation of the pulp presentation.

Future activities

The activities under task 1 and 2 have been completed with the exception of task 2.2, where - under the heading Organic solvent based introduction of new components - the activity has to be scaled up from the production of lab-scale quantities of maleinylated pulps to the production of pilot scale quantities of pulps. The work on Matrix research (task 3) is almost completed. Only the development of gMA-PP grades with high molecular weights, high crystallinities and possibly high MA concentrations are planned for the final year. For task 4 a few aspects need to be followed up. First, an automatic fibre feeding system at pilot scale has to be developed. Second, composites need to be produced from the maleinylated pulps (produced as a part of task 2. 1) by grafting. Finally the new gMA-PP grades developed as a part of task 3 need to be screened in order to select the type which gives, after compounding, the greatest improvement in mechanical properties. For task 5, one of the main requirements is the development of an industrial fibre feeding system or an adaptation of the pulp presentation (as a part of task 1) for feeding the pulp automatically to enable production of composites with good homogeneity.

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First Annual Report Summary

INTRODUCTION
The central theme of this project is the use of maleic anhydride as a means of increasing the compatibility between PP and the lignocellulosic fibres. This is one aspect of an integrated approach covering the complete production chain of AFPP, including fibre production, fibre opening, fibre treatment, matrix treatment, compounding process and production of actual prototype parts from composite materials. Activities include:

• optimisation of the physical and chemical characteristics by pulping of the fibre
• development of treatments to modify the composition of the individual fibres, including hydrophilic and hydrophobic modifications
• adaptation of the PP to increase its suitability as a matrix
• development of an efficient compounding process
• development of feeder technology applicable to dry (pre-treated) annual fibres
• optimisation of end product manufacturing techniques to fully exploit the properties of AFPP

In addition the environmental impact will be investigated by Life Cycle Analysis, while economic considerations will cover estimates of costs of the individual process steps as well as of the integrated processing chain.

OBJECTIVE
The project has the following objectives:

1. stimulation of the industrial use of annual fibre crops which can be grown in EU countries, especially indigenous crops such as flax and hemp;

2. development and optimisation of (pre)treatment and processing methods for such fibres to adapt them as reinforcers in composites with the synthetic thermoplastic polypropylene (PP);

3. development of a composite material composed of polypropylene, isotropically reinforced by randomly oriented annual fibres (AFPP) and use of such material in industrial applications - particularly automotive components.

These objectives will be pursued by an integrated approach covering the complete production chain of AFPP, including fibre production, fibre opening, fibre treatment, matrix treatment, compounding process and production of actual prototype parts from composite materials. The most important issues for the purpose of the production of AFPP-based parts with favourable properties, include:

• optimisation of the fibres' physical and chemical characteristics by the fibre opening (pulping) process;

• development of treatments to radically alter the composition of the individual fibres by introduction of new components in/on the fibres, using either physically bonded hydrophobation agents (offering the possibility of relatively easy integration with the pulping process) or being based on derivatisation by reaction with maleic anhydride (MA) producing more profound changes as well as the possibility of obtaining an addition chemical link with the matrix;

• adaptation of the PP to increase its suitability as a matrix;

• development of an efficient compounding process and, in conjunction, development of feeder technology applicable to dry (pretreated) annual fibres;

• optimisation of end product manufacturing techniques to fully exploit the properties of AFPP.

ACTIVITIES
The first objective has been to establish technical specifications and definitions for source material, intermediates and end products as well as ensuring that all testing, regardless the operator or place, will produce comparable results for flax, hemp and PP. A standard homopolymer product profile, predominantly focusing on modulus and impact properties has been defined for which round robin tests were carried out on representative fibre pulps and composite materials. For fibre pulps, the main differences arose from discrepancies in testing methods and equipment. In general, an acceptable overall understanding has been obtained, enabling comparison of the results of different tests devised to determine similar properties. For composite materials, in particular the conditioning proved very important. As a result of multiple tests, a set of conditions could be defined which would result in comparable composite properties. In addition an empirical relation was found between properties of composite end products obtained through different manufacturing techniques. The first attempts to modify the fibre used established technology based on gMA PP derivatisation of the fibre surface with water-based emulsions. The products are being evaluated, but initial results suggest that the scaling up phase will require more efforts than originally planned in order to prepare high grade material. Therefore a slight delay in producing pilot scale quantities of gMA PP pulps from emulsion is expected. Nevertheless, the gMA PP emulsion method seems very attractive since, it is potentially easy to integrate with the current fibre opening process and promising because gMA PP is known to be an excellent compatibiliser with PP.

Organic Solvent based introduction of new components to the fibre again exists in terms of a mature technology based on maleic anhydride. The development of a suitable method to derivatise fibres with MA progressed more rapidly than anticipated, and should be completed in the near future.

Work on developing optimal fluidity of the matrix to achieve wetting of the fibres and optimal matrix blend with gMA PP to achieve optimal chemical bonding between matrix and fibres is linked to developing an accurate method to determine the composition of gMA PP. For rapid measurements, an IR technique is being optimised using NMR calibration. Thus far the results appear very promising and it is expected that the method will be working early in the first part of year 2. Work on compounding includes definition of the optimal processing conditions as well as development of a practical fibre feeding system and understanding of the conditions required to graft maleinyl derivatised fibres onto the matrix. It is proposed to establish a baseline using composites based on 48 reference pulps, creating laboratory scale quantities of composites made with gMA PP pulps and with maleinylated pulps.

The most important observation made so far was the fact that it was virtually impossible to produce composite materials with acceptable fibre/matrix dispersion on basis of the pulp produced as above, either in lump or in sheet form. extruder based industrial scale compounding experiments have therefore not yet been carried out. This was unexpected since previous experiments with raw fibres and other pulps had not suggested problems would be encountered. Although in principle it would be possible to compound under more rigorous conditions, this is not an acceptable solution as this is likely to produce a `meal' instead of fibres and lead to high rates of matrix degradation. A comparison of the resultant composite properties would reflect screening of the fibre processability rather than the desired screening of the intrinsic fibre properties. Because the data of pulp based composites (even with poorly dispersed fibres) suggested better mechanical properties than obtainable with raw fibres, it decided to direct efforts towards modifications of compounding procedure in order to get the desired results. Since the objective was to scale up the process actions, such as pre-separation of the fibres by hand which would resolve the dispersion problem and allow controlled fibre feeding, were ruled out. Various process conditions were changed and a number of compatibilisers were employed. However, these simple changes did not produce any substantial improvement in the dispersion. Hence, a more radical approach was taken, applying an existing fibre treatment technology which resulted in labscale procedure which enabled proper screening of the intrinsic fibre properties in PP composites. Using this procedure, it is expected that the establishment of the baseline with the 48 reference pulps will be completed during the early part of the second year. In principle, this particular fibre treatment can be scaled up and implemented either at the end of the fibre opening process or before the compounding process. A further study was carried out to further fine tune the conditioning (to enable a more efficient screening) and test composite intermediates and products. However, as anticipated at this stage, the majority of the research, has thus far only Preliminary data, yielded so far, suggests that the relationship between gMA PP related property improvement and Mw/MA content of the modifier is not a simple linear one.