Introduction

Plastics were increasingly used in technical products. This is a result of its low efforts for production and processing in comparison with many other materials. Shaping can occur by injection moulding, where high output becomes possible with low energy consumption. Moreover, plastics have more advantages. The high transparancy of some plastics types allows for applications in optics and open new design lines. The low mass helps on construction of energy-efficient vehicles.

Plastic surfaces are usually little polar, poor wettable and little reactive. That does not hurt in many cases, where the inner properties of plastics are to be exploited. However, demands on design and surface properties are increasing. For instance, surfaces should be able to laquer, bonded or plated with metals. For this, a surface modification is often required. There are a number of commercialized approaches, which are based

• Plasma (different approaches of plasma, flame, corona treatment)
• Energy-rich irradiation (ultra-violett) or
• Etching chemicals (e.g. chromosulfuric acid)

These approaches have a number of disadvantages. Functional groups are created in the topmost surface layer by the high energy deposition. The energy deposition, however, leads to decomposition of the polymer in that layer. But this layer, with a thickness of only some nanometres, is responsible for bonding with layers to be applied next. A weak boundary layer is formed on the surface of the processed part, where the polymer molecules are fragmented with no adhesion to their own matrix. At second, the high energy does not allow for an exact control of the type of functional group.

Further processing of the surface requires a special type of function group and requires the absense of other functional groups. Finally, all these surface modifications require a separate processing step, partly with preparations and follow-up steps.

A possible way to compensate the disadvantages is the coupling of surface modifiaction with shaping, for instance by injection moulding, in one process. Thus, the expended energy for melting the polymer can be exploited by this process integration. The modification reactions are based on chemical reaction possibilities of the appropriate plastics at these high temperatures. The chemical, physical and technological conditions of this approach are investigated in our work. The advantages and the potential of the approach for applications are demonstrated.

• The method of process-integrated surface modification during moulding
• Surface modification with reactive functional polymers
• Process-integrated surface modification during FDM printing
• Surface modification with nano and micro particles
• The ForaSolv process for Cr(VI)-free surface modification of plastics for chemical metal plating
• Laser grafting
• Computer simulations
  
  

Central subject are surface modifications of plastics, where the surface layer is in melt state. This can be realised by melt processing, like moulding, or it is realised on a solidified part by taylored and mild exposing of energy, like during special laser treatment. The knowledge gained to the special surface reactions are transferred also to other fields.

The understanding of processes occuring in nanometer dimensions is related to fundamental aspect. Questions to follow are:

• How (and how fast) do reactions and interdiffusions proceed between a modifier layer of a reactive polymer layer and a plastic melt within a thin interphase layer?
• Which reactions are suitable for which plastics?
• Which mechanical forces act in the interphase layer between the flowing melt and the mould, under consideration of temperature variation?
• And how can these be exploited to the transfer of lateral structures from the mould to the plastic part surface?

Chemical model systems and simulations in different length scales are included. Monte-Carlo simulations on polymer interphases give information on how the polymer structure affects chemical bonding between modifier and melt.

The approach enables a process-integrated surface modification by efficient exploitation of resources during mass production and the efficient use of energy. It has a high potential of innovations for applications. That is why the work deals also with application aspects. It is investigated, how surface layers have to built-up to gain special surface properties. Examples are surface modification without pre-treatment for laquering, bonding or plating. Special surface modification may be realised, as used for micro fluidics, sensors, electronic displays and storages.

Knowledge of physical and chemical basics may result in a very efficient technology for mass production of thermoplastic parts with taylored modified and structured surfaces.

DFG (Deutsche Forschungsgemeinschaft)

“Immobilisation of ordered plasmonic nano structures on the surface of polymer melts”, 2019-2022

„Immobilisation of nano particles on plastic surfaces using functional polymers by surface-reactive injection moulding“, 2011-2012

„Modelling and simulation of reactions at interfaces of polymer melts for bond formation“, 2007-2009

„Chemical surface modification during injection moulding and its interaction with processing conditions“ with chair of plastics technology at TU Chemnitz, 2003-2005

„New ways for the surface activation of plastics“, DFG research group with chair of plastics technology at TU Chemnitz, 1998-2002

BMBF

“Validation of a Cr(VI)-free process for galvanic metal plating of plastics” in frame of a BMBF grand programme Validation of technological and social innovation potentials of scientific research - VIP+, 2021-2024

AiF

“Process-integrated immobilisation of optical markers on plastic part surfaces for robust and individuell part identification (Pictor)”, with Fraunhofer IFAM, Süddeutsches Kunststoffzentrum SKZ, 2021-2023

„Plastic part surfaces with permanent electrically conductive decharging surface layer“,with IOT of HS Zittau, 2014-2016

„Method for chemical surface modification of polyolefins during shaping“, with FILK Freiberg and chair of plastics technology at TU Chemnitz, 2003-2005

Volkswagen-Stiftung

„New Surface Functionalisation by Process-Integrated Surface Modification of Polyolefins“, with chair of plastics technology at TU Chemnitz, 2010-2012

„Fast Surface Reactions on Moulding“, with chair of plastics technology at TU Chemnitz, 2007-2010

The findings are regularly trasnferred to industry, e.g. in common research projects granted by the ZIM programme of AiF or direct contracts with industry.

• Studienarbeit: Praktikum oder SHK
  "Untersuchung der Eigenschaften von mikrostrukturierten chemisch funktionalisierten Kunststoffoberflächen"

• Studienarbeit: Praktikum oder SHK
  "Chemische Laserstrukturierung"

• Studienarbeit: Praktikum/Bachelorarbeit/SHK
  "Reaktives Spritzgießen für nachhaltige Oberflächenmodifizierungen während der Formteilherstellung (prozessintegriert)"
• Studienarbeit: Praktikum/Bachelorarbeit/SHK
  "DNA für Kunststoffbauteile durch Einbettung von zufälligen Partikelanordnungen in Polymerschmelzen"
  
  

• Dr. David Vehlow
• Philipp Zimmermann (PhD student)
• Kamal Meena (PhD student)

• Fraunhofer-Institut für Angewandte Materialforschung, Bremen
• Süddeutsches Kunststoffzentrum gGmbH, Erlangen
• Kunststoffzentrum Leipzig gGmbH
• Institut für Oberflächentechnik an der FH Zittau-Görlitz, Zittau